Dispensing – Molten metal dispensing – With subjacent flow guide
Reexamination Certificate
1999-07-08
2001-09-04
Kastler, Scott (Department: 1742)
Dispensing
Molten metal dispensing
With subjacent flow guide
C501S101000
Reexamination Certificate
active
06283341
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a continuous casting nozzle, in particular, a continuous casting nozzle which permits effective prevention of narrowing and clogging of the inner bore thereof through which molten steel passes in performing continuous casting of the molten steel containing aluminum such as aluminum-killed steel, which nozzle is provided for supplying the molten steel from a tundish to a mold.
THE RELATED ART
A continuous casting nozzle for casting molten steel is used for the following purposes.
A continuous casting nozzle has a function of pouring molten steel from a tundish to a mold. In continuously casting molten steel, a continuous casting nozzle is used for such purpose of preventing the molten steel from being oxidized by contacting with the open air and from splashing when the molten steel is poured from a tundish to a mold, and rectifying the flow of the poured molten steel for preventing non-metallic inclusion and slag present near or on the mold surface from being entrapped in the cast steel strand.
A refractory of a conventional continuous casting nozzle of molten steel comprises graphite (about 30 wt. %), alumina (about 60 to 70 wt. %), silica, silicon carbide and the like. However, there are following problems when aluminum-killed steel or the like is cast.
In casting the aluminum-killed steel or the like, aluminum which is added as a de-oxidizer, reacts with oxygen existing in the molten steel to produce non-metallic inclusion such as alpha (&agr;)-alumina. Furthermore, when the molten steel flows through the nozzle, the aluminum in the molten steel reacts with oxygen in the open air, to further produce alumina.
Therefore, in casting the aluminum-killed steel or the like, the non-metallic inclusion such as &agr;-alumina adheres and accumulates onto the surface of the inner bore of the continuous casting nozzle, so that the inner bore is narrowed or clogged up in the worst case so as to make the stable casting thereof difficult. Furthermore, the non-metallic inclusion such as &agr;-alumina adhered or accumulated onto the surface of the inner bore peels off or falls down, and is entrapped in the cast steel strand, thus degrading the quality of the cast steel strand.
In order to prevent the above-mentioned reduction or clogging of the inner bore of the nozzle caused by the non-metallic inclusion such as &agr;-alumina, there has widely been used the method for preventing the non-metallic inclusion such as &agr;-alumina existing in the molten steel from adhering or accumulating on the surface of the inner bore of the nozzle by means of ejecting inert gas from the inner surface of the nozzle bore toward the molten steel flowing through the inner bore (for example, the method disclosed in Japanese Patent Publication No. Hei 6-59533/1994).
However, there are problems in the above-mentioned method wherein the inert gas is ejected from the inner surface of the inner bore of the nozzle, as follows:
A large amount of the ejected inert gas causes entrapment into the cast steel strand of bubbles produced by the inert gas, to cause pinholes in the cast steel strand, thus deteriorating the quality of the cast steel. On the other hand, a small amount of the ejected inert gas causes adhesion and accumulation of the non-metallic inclusion such as the &agr;-alumina onto the surface of the inner bore of the nozzle, thus causing narrowing or clogging, in the worst case, of the inner bore.
In addition, it is substantially difficult to manufacture the nozzle which enable to uniformly eject the inert gas from the inner surface of the nozzle bore toward the molten steel flowing through the inner bore. Furthermore, when the casting is performed for a long period of time, it becomes gradually difficult to stably control the amount of ejected inert gas, since the refractory material of the continuous casting nozzle degrades. As a result, the non-metallic inclusion such as &agr;-alumina adheres and accumulates onto the surface of the inner bore of the nozzle in such manner that the inner bore is narrowed or eventually clogged up. The clogging of the nozzle by the non-metallic inclusion, particularly alumina (Al
2
O
3
) inclusion is deemed to be caused as follows:
(1) Aluminum in the molten steel is oxidized by the entrapped air in a joint portion of the nozzle refractory and the tundish refractory, and the air which passes through the refractory structure per se.
(2) Alumina inclusion is produced by the oxygen supplied from SiO which is produced through reduction of silica in a carbon-containing refractory.
(3) Alumina inclusion is produced by diffusion and cohesion of the alumina produced in the above process.
(4) Graphite and carbon on the surface of the nozzle bore are taken away and the feature of the surface of the inner bore becomes rough, and thus the alumina inclusion is apt to accumulate on the rough surface of the bore.
There is proposed a nozzle as a remedy to solve the above problem, in which a non-oxide raw material (SiC, Si
3
N
4
, BN, ZrB
2
, Sialon, etc.) that has a low reactivity with aluminum oxide is added to alumina-graphite refractory, or a nozzle consisting of the above non-oxide material itself (for example, refer to Japanese Patent Publication No. Sho 61-38152/1986).
However, it is not practical to add the above non-oxide material to the widely used alumina-graphite refractory, because the effect of preventing adhesion is not recognized unless a large amount of the non-oxide material is added, and furthermore, the corrosion resistance thereof is deteriorated when a large amount of the non-oxide material is added thereto.
Also, the nozzle consisting essentially of the non-oxide material is not suitable for practical use, since the material cost and manufacturing cost are expensive, although the substantial effect of preventing adhesion may be expected.
There is further proposed a nozzle, the refractory thereof comprising graphite-oxide raw material containing CaO, in which an oxide raw material containing CaO (CaO.ZrO
2
, CaO.SiO
2
, 2CaO.SiO
2
, and the like) produces a low-melting-point material by a reaction of CaO in the oxide raw material with Al
2
O
3
, and thus produce low-melting-point material exists in the steel (for example, refer to Japanese Patent Publication No. Sho 62-56101/1987).
However, since the reactivity of CaO with Al
2
O
3
is apt to be influenced by a temperature condition of the molten steel in casting, it is difficult to effectively produce the low-melting-point material. In addition, a large amount of CaO is required to supply when a large amount of Al
2
O
3
inclusion is contained in the steel. However, it is difficult to contain sufficient amount of CaO in the refractory of the nozzle, since spalling resistance and corrosion resistance thereof is deteriorated.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a continuous casting nozzle which may prevents alumina inclusion from adhering and accumulating on the inner surface of the nozzle, and prevents the inner bore of the nozzle from being narrowed and clogged so as to enable a stable casting, by means of forming a glass layer on the surface of the inner bore of the nozzle when the nozzle is used, thereby preventing air from being entrapped through refractory structure thus not to produce alumina, and in addition, smoothing the surface of the inner bore of the nozzle.
There is proposed as the first embodiment of the present invention, a continuous casting nozzle for casting molten steel wherein at least a surface layer of an inner bore of said continuous casting nozzle contacting with a molten steel is formed of a refractory comprising an aggregate consisting essentially of zirconia (ZrO
2
), or an aggregate comprising zirconia (ZrO
2
) as its main ingredient and melting point thereof being at least 1750 degree centigrade: from 15 to 60 wt. %; and roseki as a balance (i.e., the remaining portion of the refractory).
When the nozzle formed of a refractory having the above composition is used, zirconia (ZrO
2
) functions to main
Muroi Toshiyuki
Oguri Kazumi
Akechi Ceramics Kabushiki Kaisha
Cantor & Colburn LLP
Kastler Scott
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