JPS6317790B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an alumina-graphite cast nozzle, and particularly to a method for producing an alumina-graphite cast nozzle by modifying the nozzle raw material. Conventionally, in order to manufacture this type of casting nozzle, the method used was to thoroughly mix raw materials such as alumina and graphite at a predetermined mixing ratio, add a binder to this, knead it, shape it, and then fire it. . However, in this method, the main nozzle raw materials are generally alumina powder, which has a large specific gravity (3.98) and a small particle size, and graphite powder, which has a small specific gravity (2.2) and a large particle size, and these are mixed together. Therefore, segregation inevitably occurs due to the difference in specific gravity and particle size, resulting in the inconvenience that the nozzle obtained by kneading, molding, and firing has low strength and poor heat spalling resistance. For these reasons, the inventor of the present invention has conducted extensive research to overcome the above-mentioned drawbacks, and as a result, treated fine alumina powder with a thermosetting resin to form a thermosetting resin coating on the powder surface, By adjusting the alumina-based secondary particles of a predetermined particle size by sintering or sintering these together, the resin coating or carbonaceous coating formed on the alumina surface can reduce the specific gravity and particle size. The specific gravity and particle size are similar to those of the graphite particles mixed with this alumina, and the resin or carbonaceous coating on the surface of the secondary particles improves the compatibility between the secondary particles and the graphite particles. It was found that when kneading in the presence of a binder, it was possible to mix uniformly without causing particle segregation, and a homogeneous kneaded product could be prepared.
As a result, we have discovered a method for producing an alumina-graphite cast nozzle with high strength and excellent heat spalling resistance by molding and firing this kneaded product. Another problem with alumina-graphite casting nozzles is that when the nozzle comes into contact with the slag line, the graphite, which is a component of the nozzle, is oxidized and consumed by the oxygen in the air in the erosion reaction on the outside of the nozzle. Another problem is that due to the good thermal conductivity of graphite, non-metallic inclusions in the molten metal adhere to the inner surface of the nozzle hole during casting of the molten metal, causing nozzle blockage. On the other hand, the present inventor has developed an alumina-based method by forming secondary particles of alumina powder and treating graphite powder with a phosphate-based or borate-based binder to form a binder film. In addition to further approximating the specific gravity difference with secondary particles to enable uniform kneading,
The inorganic coating on the surface of the graphite powder can suppress the oxidative consumption of graphite by oxygen in the air outside the slag line, and can prevent alumina or alumina-silica melting after the graphite has disappeared, and furthermore, during casting, It has been found that the adhesion of non-metallic inclusions within the nozzle hole can be suppressed by a phosphate-based or borate-based coating on the surface of the graphite powder. As a result, by molding and firing this kneaded material, an alumina-graphite casting nozzle with excellent strength and heat spalling resistance, high corrosion resistance to the slag line, and an extremely long lifespan that prevents nozzle clogging is created. We have discovered that it is possible to produce That is, the method for manufacturing an alumina-graphite cast nozzle of the present invention is a method for manufacturing a nozzle using a raw material containing alumina and graphite as main components, A: treatment with a phosphate-based or borate-based binder. B: Graphite particles with a binder coating of 1 to 25 μm on the surface; B: Alumina powder with a particle size of 0.5 mm or less that has been treated with a thermosetting resin and has a resin coating of 1 to 25 μm on the surface. , alumina-based secondary particles having a resin coating or a carbonaceous coating on the surface obtained by adjusting the particle size and specific gravity to approximate the graphite particles, and kneading, molding, and firing. It is. Examples of the thermosetting resin used in the present invention include phenol resins and epoxy resins. The thickness of the film formed on the alumina powder by this thermosetting resin must be 1 to 25 μm. If it is less than 1 μm, the effect of adjusting the particle size and specific gravity will not be sufficient, and if it exceeds 25 μm, the bond between alumina particles will be hindered, resulting in a decrease in strength. However, if it is difficult to form a uniform coating with the thermosetting resin, it is not necessarily necessary to apply the coating uniformly to all of the alumina powder, and it is sufficient to form a coating on most of the alumina powder to achieve the purpose of the present invention. It can be achieved. Sintering of the thermosetting resin coated alumina in the present invention is preferably carried out in a non-oxidizing atmosphere using carbon breeze or the like. The particle size of the alumina-based secondary particles obtained here may be appropriately selected so as to approximate the particle size of graphite particles, which is another nozzle raw material, but it is usually sufficient to set the particle size to about 0.01 to 0.5 mmφ. Further, in the present invention, graphite particles treated with a phosphate-based or borate-based binder to form a coating of the binder on the surface are used as the graphite raw material. The thickness of the binder film needs to be 1 to 25 μm since the film is intended to protect the graphite powder and prevent non-metallic inclusions from adhering. However, as in the case of the thermosetting resin described above, the film formation with this binder does not necessarily have to be uniformly performed on the entire graphite powder. The nozzle raw material in the present invention has thermosetting resin-coated alumina secondary particles and graphite particles coated with a phosphate or borate binder as essential components, and may be composed of only these two components. death,
These two components include silica, zirconia, silicon carbide, silicon nitride, and metal silicon (including ferrosilicon).
A composition of three or more components containing one or more of these may also be used. The forming means in the present invention may be carried out by any ordinary method employed in nozzle manufacture, but it is particularly advantageous to employ a rubber press method, since it is possible to manufacture a dense and stronger cast nozzle. Next, examples of the present invention will be described. Example 1 10% by weight of 3% boric acid was added to graphite powder with an average particle size of 44 μm or more, kneaded, and heated to reduce the particle size.
Graphite particles coated with boric acid and having a diameter of 0.1 to 1 mm were prepared. Next, phenolic resin was added to alumina powder with an average particle size of 44 μm and kneaded to form a phenolic resin coating with an average thickness of 15 μm, and then sintered to form a phenolic resin film with an average thickness of 0.01 μm.
Alumina-based secondary particles with a diameter of 0.5 mm were prepared. 60% by weight of these alumina-based secondary particles, 25% by weight of the above-mentioned boric acid coated graphite particles, and an average particle size of 250μ
m silica particles 13% by weight and metal silicon powder 2
After adding and kneading 20 parts by weight of pitch to 100 parts by weight of the nozzle raw material obtained by blending % by weight, the kneaded product was molded using a rubber press (pressure: 1000 Kg/cm ² ). After that, this molded body was heated to 1000°C in a carbon breeze.
An alumina-graphite based cast nozzle was manufactured by firing at a temperature of .degree. Comparative Example After adding and kneading 20 parts by weight of pitch to 100 parts by weight of a nozzle raw material consisting of 60% by weight of alumina powder with an average particle size of 44 μm, 25% by weight of graphite particles, 13% by weight of silica particles, and 2% by weight of metal silicon powder, An alumina-graphite based cast nozzle was manufactured by molding and firing under the same conditions as in the previous example. Therefore, the various physical properties of the alumina-graphite casting nozzles of the present example and comparative example, the number of cracks (heat spalling resistance) when heating to 1400°C and then repeatedly cooling with water, and the slag When we investigated the degree of corrosion damage (corrosion resistance) of the outer part that comes into contact with the line part, the results are shown in the table below.

【table】

[Table] As detailed above, according to the present invention, by forming a coating of a phosphate-based or borate-based binder on graphite particles, the compatibility between alumina particles and graphite particles is improved, and In addition to suppressing oxidative consumption of graphite particles during use and preventing the adhesion of non-metallic inclusions during casting, a thermosetting resin coating is formed on alumina to form secondary particles, and the specific gravity and particle size of the alumina are reduced. By making the diameter similar to graphite particles, which is another nozzle raw material, it is possible to prepare a homogeneous kneaded product without segregation when kneading the raw material particles, and it has high strength and excellent heat spalling resistance when molded and fired. It has remarkable effects such as being able to manufacture alumina-graphite based cast nozzles.

Claims (1)

[Claims] 1. A method for manufacturing a nozzle using a raw material containing alumina and graphite as main components, A: treated with a phosphate-based or borate-based binder to form a 1-25 μm layer of the above-mentioned material on the surface. Graphite particles with a binder coating formed thereon; B: Alumina powder with a particle size of 0.5 mm or less that has been treated with a thermosetting resin and has a resin coating of 1 to 25 μm on its surface, so as to approximate the graphite particles. A method for producing an alumina-graphite casting nozzle, comprising: kneading, molding, and firing alumina secondary particles having a resin coating or a carbonaceous coating on the surface obtained by adjusting the particle size and specific gravity. .