EP0059805B1

EP0059805B1 - Porous nozzle for molten metal vessel

Info

Publication number: EP0059805B1
Application number: EP19810301019
Authority: EP
Inventors: Junichi Ato
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-03-11
Filing date: 1981-03-11
Publication date: 1985-02-13
Also published as: EP0059805A1; DE3168852D1

Description

This invention relates to an improvement in a porous nozzle which is adapted to be arranged at the bottom of a molten metal vessel. The object of this is to separate by flotation, the non-metallic inclusions in molten metal in said vessel and to prevent slag involvement and nozzle opening closure. More particularly it relates to an improvement of a porous nozzle mounted at the bottom of a ladle or tundish of the molten metal vessel.
Generally the nozzle of a ladle or tundish container is constructed of a dense refractory. However, nonmetallic inclusions in the molten steel often adhere in the nozzle opening during let down of the melt to cause contraction of the nozzle aperture and eventually closure, this often brings about difficulties in pouring the melt. To prevent these disadvantageous phenomena, therefore, it has been proposed in FR-A-2167284 to provide a refractory porous nozzle adapted for arrangement at the bottom of a molten metal vessel, wherein;

said porous nozzle is formed as a single body including a flange portion and a frusto-conical or cylindrical portion;
the outer peripheral surface of the main body of said porous nozzle is enclosed in a gas-tight shell;
. a gas pool is provided between the bottom surface of the flange portion and the outer peripheral surface of said frusto-conical or cylindrical portion, and the inner peripheral surface of said shell, and the gas pool communicates with an inert gas feed pipe.

Further, for another purpose, in order that the non-metallic inclusions in the molten steel within the vessel are removed to make a purified and good quality molten steel there is also carried out a method in which separately from a porous nozzle, a refractory porous plug is arranged at the bottom of a container such as ladle or tundish, and inert gases are jetted into the molten steel through the pores of the porous plug. The non-metallic inclusions are flotated and separated and the purity of said molten steel is improved. There is another method which does not use a porous plug. To take a tundish for example, a refractory weir is provided within said vessel to change the flow of the molten steel, and the non-metallic inclusions in the molten steel are separated by flotation.
Because the dimensions 6f the tundish are limited because of structure and design of a continuous casting plant, however, it is difficult to make an effective weir shape or arrange an effective weir within a comparatively narrow tundish, and it is known that not only the tundish design becomes complicated but also it is difficult to fix a weir within the tundish at all.
Further, although the porous nozzle arranged in a conventional tundish prevents contraction and closure of the nozzle, during continuous casting said nozzle may cause entrainment of the non-metallic inclusions, slag, etc. which then float up on the turbulence generated at the upper portion of the nozzle opening when the ladle is replaced, thereby causing a lowered quality of steel.
Furthermore, although the method in which a porous plug is provided at the bottom of a tundish and inert gases are jetted into the molten steel is effective for separating the inclusions, the plug must be arranged at a position different from that of the nozzle so that a complete effect cannot be exhibited, particularly for preventing slag involvement, due to the turbulence generated at the upper portion of the nozzle opening when replacing the ladle as referred to above.
In view of the various demerits of conventional methods particularly of FR-A-2167284, the invention provides, in one aspect, that the flanged portion and the frusto-conical or cylindrical portion of the nozzle are formed with a gas seal member therebetween, and a gas pool in communication respectively with each of said portions.
In another aspect of the invention it is provided that a fine porous refractory layer is interposed between said nozzle portions, said layer being formed of a finer material than the nozzle body; and wherein the gas pool communicates directly with the flange portion, a portion only of said gas being able to pass through the said layer.
In a further aspect of the invention the porous nozzle is formed as a single body including a flange portion arranged superior to the frusto-conical or cylindrical portion, and wherein the gas pool is formed over at least part of the outer peripheral surface of the flange portion, a gas vent in communication with said gas pool being disposed inferior to said flange portion and in the outer peripheral surface of the cylindrical or frusto-conical portion.
The invention will now be described more in detail with reference to the accompanying drawings which show some embodiments of the invention in which

Figure 1 shows a vertical section of a porous nozzle according to the invention in which the bottom of the flange portion communicates with a gas pool disposed at a cylindrical outer periphery;
Figure 2 shows a vertical section of a porous nozzle of the invention in which the flange portion and the frustoconical portion are provided with a sealing member;
Figure 3 shows a vertical section of a porous nozzle in accordance with the invention in which the flange portion and the cylindrical portion are provided with a fine porous refractory layer; and
Figure 4 is a vertical sectional view showing a porous nozzle of Figure 2 disposed at the bottom of a molten metal vessel.

In Figure 1 a porous nozzle is arranged at the pouring-out portion at the bottom of a molten steel vessel, and is mounted in a nozzle socket in a central portion of a nozzle-receiving brick. The outer peripheral surface of said brick is in contact with a lining refractory brick of said vessel bottom. This embodiment of the invention provides an excellent porous nozzle in which the vessel is surrounded with a steel shell 3 in such a manner that an annular gas pool 2 is provided over at least a part, or the whole of the outer peripheral surface of a porous refractory layer constituting the main body of a porous nozzle 1, and at least over a part, or the whole, of the flange portion at the lower end of a flange porous layer 1 a. The gas pool 2 communicates with a vent 2a in the outer peripheral surface of the cylindrical nozzle portion. Inert gas is jetted through a piping from the outside into a nozzle opening 11a from the upper surface of said porous refractory layer 1 a constituting the flange portion of the porous nozzle and from the inner periphery surface of a porous refractory layer 1b constituting the nozzle cylindrical portion. By doing this it is readily possible to separate the non-metallic inclusions in the molten steel by flotation, while preventing the nozzle opening from closure and slag involvement.
Figure 2 shows an embodiment of a pourous nozzle where the porous refractory layer of Figure 1 is doubled. That is, this porous nozzle is formed such that the porous refractory layer 1 a is isolated by a sealing member 5 from the porous refractory layer 1 b constituting a frusto- conical portion whereby the function of causing the inert gases to jet upwardly in the molten steel is separated from the function of jetting said gases into the nozzle opening 11 a. The present porous nozzle has in one unit means for jetting gases to the upper surface of the flange by permeating the pores of the flange porous refractory layer. These gases pass through a gas blowing opening 4 into gas pool 2 which is provided at the circumference of the lower end of the flange of said porous nozzle. The nozzle also provides means for jetting the gases into the nozzle opening 1 a, by permeating the pores of the porous refractory layer 1 b of the frust-conical nozzle portion via gas pool 2a surrounded by a steel shell 3. A sealing member 5 separates said two means, and may be made of silica, alumina or any other desired sintered refractory which completely prevents gas leakage. Thus, gas leakage to the outside is prevented and gas permeation is prevented between the refractory porous layer of the flange portion 1 a and the porous refractory layer 1 b of the frusto-conical nozzle portion via gas pool 2a surrounded by a steel shell 3. A sealing member 5 separates said two means, and may be made of silica, alumina or any other desired sintered refactory which completely prevents gas leakage. Thus gas leakage to the outside is prevented and gas permeation is prevented between the refractory porous layer of the flange portion 1 a and the porous refractory layer 1b of the frusto-conical nozzle portion by means of said sealing member 5.
The reason for separating the gas ejection mechanism in the upper flange portion from that in the nozzle opening 1 a a is that in a porous nozzle for a tundish, owing to the physical pressure difference between the molten steel static pressure within the tundish, which is received by the upper surface of the flange, and the molten steel kinetic pressure (pressure is reduced based on the- Bernoulli's theorem) which is received by the inner peripheral surface of the nozzle during the time when the molten steel flows down within said nozzle opening, it is necessary to separately adjust the gas blowing pressure in the flange portion from that into the nozzle opening 11 a.
The pressure of the gas blown into the nozzle opening 1 a makes it possible to prevent the nozzle from contraction and closure by forming a gas curtain in the inner peripheral surface of the nozzle opening. However, if gas pressure is unnecessarily raised the inert gases pass into the molten steel when the melt flows down into the nozzle opening, and therefore there is an unfavourable possibility that pin holes may occur in the solidifying process of the molten steel. Further, the present invention has advantages in that when the lower portion of said porous nozzle is closed to metal passage it suffices to eject gas only from the upper surface of the flange because of the plurality of gas openings therein. Thus, if necessary, gas ejection and gas pressure may be easily adjusted so as to save inert gas.
According to the porous nozzle of Figure 3, the porous refractory layer of the main body of said porous nozzle is constructed in such a way that between the porous refractory layer of the flange portion and that of the frusto-conical portion there is formed a fine porous refractory layer 6 which has a greater gas resistance than the porous refractory layer of the main porous body. Inert gas is therefore primarily guided from the gas inlet 4 and the gases are jetted, via the gas pool 2, from the upper surface of the flange portion permeating the pores of the porous refractory layer 1 a. Meanwhile, a part of the inert gases permeates the frusto-conical porous refractory layer 1 b, through the fine porous refractory layer 6 thereby to be jetted into the nozzle opening 11 a. When a part of the inert gases permeates through said fine porous refractory layer 6 the gas pressure is considerably reduced so that the amount of the gas entering the nozzle opening 11 a is decreased and therefore, the molten steel will not be saturated with inert gas.
In the drawings the fine porous refractory layer is not flat in its sectional configuration but it may be of optional shape, and naturally the thickness of said layer is optionally selected and said layer is formed in a shape and thickness answering particular conditions depending upon the permeation and resistance of the gas.
Figure 4 is a schematical sectional view of the porous nozzle of Figure 2, in which the porous nozzle wherein the ejection mechanism from the flange surface is separated from that into the nozzle opening, is arranged at the bottom of a molten metal vessel. Further, Fig. 4 is also a sectional view of the porous nozzle 1 as arranged, in which a through hole is provided at the bottom of a vessel where a steel casing 7 is lined with refractory bricks 8, said porous nozzle being mounted in a central zone of the inner peripheral surface of the nozzle-receiving brick 9 fixed in said through hole. Fig. 4 is exemplified with a porous nozzle connected at its lower end to a sliding nozzle 10, but said nozzle can naturally be applicable to melt discharging nozzles which adopt a stopper system as a nozzle opening and closing mechanism.
The invention will now be described by way of example.
By mounting the porous nozzle (shown in Fig. 2) of the invention in a tundish there was carried out a continuous casting operation for steel plates for motor-cars, but as expected initially there was neither contraction nor closure of the nozzle. Nor was then any slag involvement when the ladle was replaced. Moreover, even the index of the non-metallic inclusions was reduced by 30-40% compared with conventional porous nozzles to obtain a very satisfactory result. The conditions of carrying out the operation were as follows:
Blow amount of inert gas (Ar):
The more the porous nozzle of the invention increases its width within an operable range in the length and in the width direction of the flange, the more it produces its beneficial effects. However, the shape and capacity of the melt vessel and the problems of said vessel when operating must be taken into consideration to find the optimum width and thickness of the flange.
In the drawings the upper surface of the flange is shown in a flat configuration, but the shape is not limited to said configuration and no troubles in use even if the surface is curved or a little uneven.
The important thing is that the porous nozzle ejects an inert gas toward the upper portion of the molten metal. The porous nozzle of the invention has been described in detail particularly with respect to a tundish nozzle for molten steel, but the present invention is very useful industrially in that it is applicable to vessels for other molten metals such as copper.

Claims

1. A refractory porous nozzle adapted for arrangement at the bottom of a molten metal vessel wherein: said porous nozzle (1) includes a flange portion (1a) and a frusto-conical or cylindrical portion (1b), the outer peripheral surface of the main body of said porous nozzle is enclosed in a gas-tight shell (3), a gas pool (2) is provided between the bottom surface of said flange portion and the outer peripheral surface of said frusto-conical or cylindrical portion and the inner peripheral surface of said shell, and the gas pool communicates with an inert gas feed pipe (4); characterized in that the flange portion (1a) and the frusto-conical or cylindrical portion (1 b) of the nozzle are formed with a gas seal member (5) therebetween, and a gas pool (2, 2a) in communication respectively with each of said portions (1 a, 1 b).

2. A refractory porous nozzle adapted for arrangement at the bottom of a molten metal vessel, wherein said porous nozzle (1) includes a flange portion (1a), and a frusto-conical or cylindrical portion (1b) the outer peripheral surface of the main body of said porous nozzle is enclosed in a gas-tight shell (3) and a gas pool (2) is provided between the bottom surface of said flange portion and the outer peripheral surface of said frusto-conical or cylindrical portion, and the inner peripheral surface of said shell, and said gas pool communicates with an inert gas feed pipe (4); characterized in that a fine porous refractory layer (6) is interposed between said nozzle portions (1 a) and (1 b); said layer (6) being formed of a finer material than the nozzle body, and wherein the gas pool communicates directly with the flange portion (1 a), a portion only of said gas being able to pass through the layer (6).

3. A refractory porous nozzle adapted for arrangement at the bottom of a molten metal vessel wherein said porous nozzle (1) includes a flange portion (1 a) and a frusto conical or cylindrical portion (1b), the outer peripheral surface of the main body of the porous nozzle is enclosed in a gas-tight shell (3), a gas pool (2) is provided between the bottom surface of said flange portion and the outer peripheral surface of said frusto conical or cylindrical portion, and the inner peripheral surface of said shell, and the gas pool communicates with an inert gas feed pipe (4); characterized in that the porous nozzle (1) is formed as a single body including a flange portion (1a) adapted to be superior in use to the frusto-conical or cylindrical portion (1b), and wherein the gas pool (2) is formed over at least a part of the outer peripheral surface of the flange portion (1a); a gas vent (2a) in communication with said gas pool (2) being disposed inferior to said flange portion (1a) and in the outer peripheral surface of the cylindrical or frusto-conical portion (1b).

4. A molten metal vessel characterized by the inclusion of a refractory porous nozzle as claimed in claim 1, 2 or claim 3.