Dispensing – Processes of dispensing – Molten metal
Reexamination Certificate
1998-02-04
2001-11-27
Pyon, Harold (Department: 1772)
Dispensing
Processes of dispensing
Molten metal
C164S337000, C164S437000, C222S591000, C222S606000, C222S607000, C428S034600, C428S036910, C428S212000, C428S213000
Reexamination Certificate
active
06321953
ABSTRACT:
The present invention relates to an immersion nozzle used for discharging molten steel, and in particular, to a composite immersion nozzle comprising two or more materials.
In a facility for continuous casting, an immersion nozzle is used when molten steel is injected from tundish into a mold. This immersion nozzle is immersed from its tip to slag line into molten steel filled in the mold and it is provided with functions to prevent splashing when molten steel is injected, to avoid oxidation of the injected molten steel as it is brought into contact with the air, and further to prevent suspended matters from being caught and intermingled in molten steel (hereinafter referred as “slag”) such as mold powder or other foreign objects on the surface of the molten steel.
The immersion nozzle as described above should be made of a material, which is very unlikely to cause closure of the nozzle, has corrosion resistant property to molten steel or slag, high spalling resistant property and has high hot strength. However, in case it is made of a single type of refractory material, it is difficult to have the nozzle, which can adapt to complex environment because the upper end, the slag line and inner surface of the nozzle, into which molten steel is injected, are used under different environmental conditions. In this respect, various types of composite immersion nozzles have been known in the past. For example, there have been proposed the following types of nozzles: a nozzle comprising a main body made of alumina-carbon type refractory material and a zirconia-carbon type refractory material layer integrally molded on a slag line portion (outer surface of the nozzle) which is brought into contact with slag (JP-A-3-243259), or a nozzle comprising a main body made of alumina-carbon type refractory material and a layer to prevent alumina build-up on inner surface of the nozzle to avoid clogging of nozzle, or a nozzle comprising a main body made of alumina-carbon type refractory material and a layer to prevent corrosion in inner surface of the nozzle to avoid corrosion of the nozzle (JP-B-6-4509). To prevent cracking, a composite immersion nozzle is known, which attains the purpose by adjusting blending or property of materials of each component, for example, a nozzle comprising a main body material and an inner side material with difference of expansion coefficient within 0.15% (JP-A-56-33155), or a nozzle produced by limiting quantity of zirconia, i.e. a material with high expansion coefficient (JP-A-56-41053).
In the composite immersion nozzle, cracking may occur due to thermal stress when receiving molten steel because the material properties of the components are different. To prevent cracking, JP-A-56-41053 describes the condition that expansion coefficient of the material on inner side of the nozzle should be equal to or lower than that of the material of the nozzle main body and that the difference of the expansion coefficient between the two materials should be within about 0.15%. JP-A-56-33155 describes the prevention of cracking by limiting the blending quantity of zirconia (to 90% or less) in the material on the inner side of the nozzle to decrease expansion coefficient.
However, such conditions cannot be maintained in many cases in order to ensure good quality of cast piece or to attain stability of molten steel injection.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a composite immersion nozzle, which comprises two types or more of materials, whereby there is no restriction on the properties of the materials such as thermal expansion coefficient, and thermal stress on the nozzle is reduced to prevent cracking, while fully utilizing the properties required for each of the materials such as corrosion resistant property or property to prevent alumina build up on the nozzle.
The present inventors have been making efforts to study shapes of the immersion nozzle, in which cracking is most unlikely to occur by simulating occurrence of various types of cracks generated in the immersion nozzle and phenomenon of cracks by calculation of thermal stress. During the course of the study, it has been found that, in case of a composite immersion nozzle comprising two types or more of materials, due to arrangement of the materials, there is difference in the value of thermal stress, which is the direct cause of cracks generated in nozzle even when the shape of the entire nozzle is the same, and the concept of the present invention has been attained.
The composite immersion nozzle of the present invention comprises two types or more of materials, and it is characterized in that, when a material having higher thermal expansion coefficient than the main body of the nozzle is arranged on inner side, thickness of the material arranged on the inner side is less than 25% to total thickness, and also that, when a material different from that of the nozzle main body is arranged on outer side of the nozzle, the material of the nozzle main body is placed between the material of the inner side and the material of the outer side.
REFERENCES:
patent: 4877705 (1989-10-01), Polidor
patent: 5086957 (1992-02-01), Ozeki et al.
patent: 2135918A (1984-09-01), None
patent: 9-277031 (1997-10-01), None
N. Lange, ed., Handbook of Chemistry, 9th ed., p. 1678, 1956.
Nakamura Ryosuke
Uchida Shigeki
Yoshikawa Michinori
Armstrong Westerman Hattori McLeland & Naughton LLP
Nolan Sandra M.
Pyon Harold
Shinagawa Refractories Co. Ltd.
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