Dispensing – Molten metal dispensing – With subjacent flow guide
Reexamination Certificate
2000-04-17
2001-07-10
Kastler, Scott (Department: 1742)
Dispensing
Molten metal dispensing
With subjacent flow guide
C501S101000
Reexamination Certificate
active
06257466
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a continuous casting nozzle for enabling effective prevention of narrowing or clogging of the nozzle bore through which molten metal including steel passes during continuous casting of the molten metal including steel containing aluminum such as aluminum-killed steel used for automobile sheet.
THE RELATED ART
A continuous casting nozzle for casting molten steel is used for the purposes as indicated in the following.
As for continuous casting molten steel, a continuous casting nozzle is used for 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 molten steel poured for preventing non-metallic inclusion and slag present near or on the mold surface from being entrapped in the cast steel strand.
Material of a conventional continuous casting nozzle of molten steel comprises such material as graphite, alumina, silica, and silicon carbide. However, there are following problems in the case of casting aluminum-killed steel and the like.
As for the aluminum-killed steel and the like, aluminum, which is added as a de-oxidizer and a stabilizing element in the steel, reacts with oxygen existing in the molten steel to produce non-metallic inclusion such as &agr;-alumina. Therefore, in casting the aluminum-killed steel and the like, the non-metallic inclusion such as alumina adheres and accumulates onto the surface of the bore of the continuous casting nozzle, so that the bore is narrowed or clogged up in the worst case, which makes stable casting difficult. Furthermore, the non-metallic inclusion such as alumina adhered or accumulated onto the surface of the bore is peeled off or falls down, and is entrapped in the cast steel strand, thus degrading the quality of the cast steel strand.
To prevent the above-mentioned narrowing or clogging of the bore caused by the non-metallic inclusion such as alumina, there is proposed a commonly used method for preventing the non-metallic inclusion such as alumina existing in the molten steel from adhering or accumulating on the surface of the bore of the nozzle, wherein inert gas is ejected from the inner surface of the nozzle bore toward the molten steel flowing through the bore (for example, Japanese Patent Publication No. Hei 6-59533/1994).
However, there are problems of the above mentioned method as described below wherein the inert gas is ejected from the inner surface of the nozzle bore. A large amount of the ejected inert gas causes entrapment of bubbles produced by the inert gas into the cast steel strand, resulting in defects caused by pinholes. On the other hand, a small amount of the ejected inert gas can not prevent adhesion and accumulation of the non-metallic inclusion such as alumina onto the surface of the bore of the nozzle, thus causing narrowing or clogging, in the worst case, of the bore.
Additionally, it is difficult to uniformly eject the inert gas from the inner surface of the nozzle bore toward the molten steel flowing through the bore because the injected gas can not be distributed along the bore. Arid in the case that the casting is performed in a long period of time, a stable control of the amount of ejected inert gas becomes gradually more difficult according as the structure of the material consisting of the continuous casting nozzle degrades. As a result, the non-metallic inclusion such as alumina adheres and accumulates onto the surface of the bore of the nozzle so that the bore is narrowed or clogged up eventually.
It is considered that the clogging of the nozzle by the non-metallic inclusion, specially by alumina inclusion, is caused as described below.
(1) Alumina inclusion is produced from aluminum existing in the steel by secondary oxidation, such as oxidation by air passing through a refractory junction and refractory structure or oxidation by supplying oxygen caused by reduction of silica in a carbon-containing refractory.
(2) Alumina inclusion is produced by diffusion and cohesion of the alumina produced in the above process.
(3) Carbon on the surface of the nozzle bore vanishes and the surface of the bore becomes rough and thus the alumina inclusion is apt to accumulate on the rough surface of the bore.
On the other hand, as a counterplan in view of nozzle material, an alumina-graphite nozzle is proposed which contains a non-oxide raw material such as SiC, Si
3
N
4
, BN, ZrB
2
, SIALON, etc. as a component having a low reactivity with aluminum oxide, or a nozzle consisting of the non-oxide material itself is proposed (for example, Japanese Patent Publication No. Sho 61-38158/1986).
However, this counterplan is not practical in the case of the alumina-graphite nozzle, because the adhesion preventing effect is not recognized and further corrosion resistance is decreased unless much of the non-oxide material is added. Also, the nozzle consists of only the non-oxide material is not suitable for practical use in view of material cost and manufacturing cost, although a substantial effect is expected.
A nozzle consisting of graphite-oxide raw material containing CaO is proposed for producing low-melting-point material by a reaction of CaO in an oxide raw material containing CaO (CaO.ZrO
2
, CaO.SiO
2
, 2CaO.SiO
2
, etc.) with Al
2
O
3
and forming the low-melting-point material in steel (for example, Japanese Patent Laid-Open Publication No. Sho 62-56101). However, reactivity of CaO with Al
2
O
3
is apt to be influenced by the temperature of the molten steel in casting and there is a case that the amount of CaO is not sufficiently secured for satisfying spalling resistance and erosion resistance when a plenty of Al
2
O
3
inclusion is contained in steel. And furthermore, ZrO
2
which is melted away from the refractory material into steel will not float up from molten steel because of a high density.
OBJECT OF THE INVENTION
The object of the present invention is to provide a continuous casting nozzle having following features.
(1) A glassy layer should be formed at the surface of the bore of the nozzle during casting, thereby preventing air from being penetrated in molten steel through refractory structure, which prevents alumina from being produced.
(2) The erosion of the bore should be prevented by reaction products having a low-melting-point on account of a reaction between an aggregate in the refractory and alumina in the steel.
And a smooth surface of the nozzle bore should be produced without the use of mechanical means such as the ejecting of an inert gas.
(3) A continuous casting nozzle should be provided which is able to prevent the bore from narrowing or clogging economically, comparatively easy and stably.
SUMMARY OF THE INVENTION
In the first embodiment of the present invention, the surface layer of the bore of a continuous casting nozzle contacting with molten steel is formed of a refractory material comprising silicon carbide from 1 to 10 wt % , aggregate consisting of alumina or an aggregate which comprises alumina as main component whose melting point is not less than 1800 degree C. from 15 to 60 wt %, and roseki as a main component from 30 to 84 wt % .
The second embodiment of the present invention, the surface layer of the bore of a continuous casting nozzle contacting with molten steel is formed of a refractory material comprising silicon carbide from 1 to 10 wt % , aggregate consisting of alumina or an aggregate which consists of alumina as main component whose melting point is not less than 1800 degree C. from 15 to 60 wt %, and roseki as a main component from 30 to 84 wt %, said refractory material being added binder, kneaded, formed, and sintered in non-oxidizing atmosphere.
It is preferable that said roseki comprises a roseki having a diameter equal to or less than 250 &mgr;m contains equal to or less than 60 wt % relative to the whole of the roseki so as to form a glass layer at the surface contacting with the molten steel.
Further it is preferable that the roseki is calcinated at a temperature equal to or
Muroi Toshiyuki
Oguri Kazumi
Akechi Ceramics Kabushiki Kaisha
Cantor & Colburn LLP
Kastler Scott
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