MULTI-STEPPED IMMERSION NOZZLE FOR CONTINUOUS CASTING

Abstract: This invention is characterized by providing a plurality of steps for the molten steel flowing hole of the immersion nozzle for continuous casting, in which inner diameters d₁, d₂, and d₃ of said molten steel flowing hole at stepped parts are in such relations that d₁ > d₂ > d, or d₁ > d₂ > d₃ > d, where d is the main inner diameter, and the inner diameter d₂ or d₃ at the part immediately above the molten steel discharge opening is such that (d + 10 mm ≧ d₂ or d₃), and the material of the inner peripheral wall near the molten steel discharge opening is desirably boron-nitride-carbon. Such a composition as above is very effective in preventing deposit and adhesion of Al₂O₃ and is capable of improving the life of nozzle 50% over that of the conventional one.

Description: TECHNICAL FIELD This invention relates to an improvement in a submerged nozzle for continuous casting, and more particularly to a submerged nozzle for continuous casting, the molten steel pouring hole of which is provided with a plurality of steps. PRIOR ART A system of blowing inert gas is well-known as means for preventing a nozzle from fouling, which impedes a multicontinuous casting, and which is caused by adhesive sedimentation of an Aℓ₂O₃ deposit to the inner wall of the submerged nozzle. Further, in such kind of continuous casting there is proposed (as in JP Utility Model Publication No. 61-6987) a technique that intends to swallow up the scum and pour the melt in the non-oxidated state by means of a long nozzle which is connected to a ladle nozzle and only the submerging portion of which is made large-diameter, said submerging portion being submerged into the molten steel in a mold. It is known that said system of blowing inert gas has the following disadvantages. (1) As will be seen from Fig. 7, the fouling of the nozzle caused by the adhesion of deposit such as of Al₁₀O₃ takes place in the upper portion within the nozzle and in the inner surface near pourring outlet. (2) If a gas blowing nozzle as illustrated in Fig. 6 is used to avoid the disadvantage (1) above, the inner surface of the pouring outlet of the nozzle vigorously melts down due to the buddling agitation aciton of the inert gas. DISCLOSURE OF THE INVENTION The inventors of this invention have made their extensive researches in an attempt to avoid the various drawbacks of the known system. As a result, they have been successful in developing a multi-stepped submerged nozzle of the present invention. The technical constitution of the invention is characterized by the provision of a plurality of steps, having inside diameters d₁ and d₂, or d₁, d₂ and d₃, in a molten steel pouring hole of a submerged nozzle for continuous casting, the nozzle having a main pipe of diameter d, the dimensions of the inside diameters of the steps to the inside diameter d of the main pipe being d₁ > d₂ > d or d₁ > d₂ > d₃ > d, and the steps being arranged in the direction of the bottom of the nozzle, and the respective spaces between said steps d₁ and d₂, or d₁, d₂ and d₃, consist of the main pipe of inside diameter d. The inside diameter d₂ or d₃ immediately above the molten steel pouring outlet is preferably d + 10mm ≧ d₂ or d₃, and the material of the inner peripheral wall near the pouring outlet is boron nitride-carbon. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 and 2 are vertical sectional views showing embodiments of the invention, Figs. 3 and 4 show relationships among the state, quantity and speed of the melt flow in the molten steel pouring hole of the present submerged nozzle; and Figs. 5 to 7 are vertical sectional views showing a conventional submerged nozzle and states of deposition of Aℓ₂O₃ to the nozzle. BEST MODE OF CARRYING OUT THE INVENTION In order to solve the problems of a submerged nozzle in multi-continuous casting the following matters are important. a) A deposit of Aℓ₂O₃ is likely to take place in the upper, inner periphery of the submerged nozzle and the inner surface near the pouring outlet, and it is important to solve the means for avoiding the deposition. b) It is also important to select a material to which an Aℓ₂O₃ deposit hardly adheres. Also in an attempt to solve these problems the inventors of this invention have made the invention. EXAMPLES The invention will now be described more in detail, by way of some examples, with reference to the accompanying drawings. Figs. 1 and 2 are vertical sectional views showing embodiments of nozzles of the present invention. Fig. 1 is an embodiment where the steps are double and the inside diameters of the molten steel pouring hole are d₁ > d₂ > d, while Fig. 2 is another embodiment where the steps are triple and the inside diameters of the pouring hole are d₁ > d₂ > d₃ > d. Fig. 3 (two-stepped nozzle)and Fig. 4 (three-stepped nozzle) show the flow (shown with arrows) of the molten steel within the pouring hole of the submerged nozzles. As will be understood from Figs. 3 and 4, a turbulence of flow takes place i.e. the flow of the molten steel changes in the pouring hole whereby the deposition of Aℓ₂O₃ to the inner wall is effectively prevented. In providing such steps in the submerged nozzles it has been noticed from experiments that the optimum inside diameters of the molten steel pouring hole is d₁ > d₂ > d in the case of a double-stepped nozzle, and in the case of a triple-stepped nozzle the optimum diameters are d₁ > d₂ > d₃ > d. It has further been observed from the experiments that the inside diameter d₂ (double steps) or d₃ (triple steps) of the molten steel pouring hole immediately above the melt pouring outlet is preferably d + 10mm ≧ d₂ or d₃. On the other hand, it has also been noticed that the effect of preventing Aℓ₂O₃ from deposition to the pouring hole is significant by using boron nitride-carbon (BN-C) as the material of the inner peripheral wall near the molten steel pouring hole. The functions and effects of the invention will be enumerated as mentioned hereunder. (1) A plurality of steps are provided in the inside diameters of the molten steel pouring hole of a submerged nozzle to prevent the melt flow from staying and generate a turbulence whereby Aℓ₂O₃ is prevented from deposition. (2) To product a significant effect for preventing Aℓ₂O₃ from deposition a material for avoidance of deposition of Aℓ₂O₃ is arranged in the inner wall near the molten steel pouring outlet. (3) The life of the submerged nozzle of the invention has been improved by 50% compared with the known articles to enable a multi-pouring casting to be easily carried out. INDUSTRIAL FIELD OF THE INVENTION The invention is used for a submerged nozzle for continuous-pouring casting.

Claims: A submerged nozzle for continuous casting comprising a molten steel pouring hole having a main pipe of inside diameter d, and a molten steel pouring outlet at the bottom of the nozzle, characterised in that a plurality of steps, having inside diameters d₁, and d₂, or d₁, d₂ and d₃, are provided in the molten steel pouring hole, the dimensions of the inside diameters of said steps to the inside diameter d of the main pipe is d₁>d₂>d or d₁>d₂>d₃>d, the steps being arranged in the direction of the bottom of the nozzle in the order of the inside diameters d₁ to d₃, and in that the respective spaces between said steps d₁ and d₂ or d₁, d₂ and d₃ consist of the main pipe of inside diameter d. A multi-stepped submerged nozzle according to claim 1, characterised in that steps of the same inside diameter d are doubly arranged. A multi-stepped submerged nozzle according to claim 1, characterised in that the inside diameters d₂ or d₃ respectively, immediately above the molten steel pouring outlet correspond to d + 10 mm being greater than or equal to d₂ or d₃ respectively. The multi-stepped submerged nozzle according to claim 1, characterised in that the material of the inner peripheral wall near the molten steel pouring outlet is boron nitride-carbon.

Inventors: KANAMARU KOZO, KURASHINA YUKINOBU, NANBA YASUTOSHI, KANAMARU, KOZO, KURASHINA, YUKINOBU, NANBA, YASUTOSHI, KANAMARU, KOZO, 47, MUKAE, JOBANSEKIFUNE-CHO, KURASHINA, YUKINOBU,, NANBA, YASUTOSHI, 77-1, MUKAE, JOBANSEKIFUNE-CHO
Applicants: SHINAGAWA REFRACTORIES CO, SHINAGAWA REFRACTORIES CO., LTD.
Application year: 1991
Main classification: B22D11
IPC codes: B22D41, B22D11