Title of Invention

NOZZLE FOR INTRODUCING A LIQUID METAL INTO A MOULD FOR CONTINUOUS CASTING OF METALS

Abstract

(57) Abstract: The invention relates to a nozzle (1) for intro-ducing a liquid metal into a mould for continuoue casting of metals, of the type comprising a tubular first part (2) , one end of which is intended to be connected to a receptacle enclosingr the said liquid metal, and the other-end <4> of which open into a hollow second part <6) in which at least one portion (2S) of the internal space (7) is oriented substantially perpendicularly to the eaid tubular first part <2> , the eaid portion (29) comprising at each of its ends at least one orifice <10, 11) intended to emergre into the casting space of the said mould, characteriaed in that it comprises an obstacle placed in the path of the liquid metal inside the said tubular first part C2) or in its extension, the said obstacle consisting of at least one perforated component intended to divert the metal from its preferential trajectory inside the nozzle. PRICE: THIRTY RUPEES

Full Text

MYO 95.6S NOZZLE FOR INTRODUCING A LIQUID METAL INTO A MOULD FOR CONTINUOUS CASTING OP MeTALS The invention relates to the continuous casting Of metals, especially of steel. More precisely, it relates to the tubes made of refractory material, known as "nozzles" which, usually, are connected by their upper end to the receptacle used as storage container for liquid metal/ and whose lower end is immersed in the liquid metal melt present in the mould where the solidi¬fying of the metal product is to be initiated. The primary role of these nozzles is to protect the jet of liquid metal from atmospheric oxidation in its travel between the receptacle and the mould. By virtue of appropriate conficrurations of their lower end, they also i make it possible to orient favourably the flows of the liquid metal in the mould in order that the solidifying of the product should take place in the best possible conditions. The casting may take place in a mould which is to impart to the product a section of very elongated rec¬ tangular shape/ which is usually referred to by the expression "flat product". In iron and steel manufacture this is the case when steel is cast in the foirm of slabs, that is to say of products which are approximately 1 to 2 m in width and generally of the order of 20 cm in thickness, but which can go down to a few cm on some recent plants known as "thin slab casting machines". In these examples the mould is made up of stationary walls which are energetically cooled on their face which is not in contact with the metal. Experiments are also being carried out with plants which make it possible to obtain, directly by solidifying the liquid metal, steel strips a few mm in thickness. To do this, use is made of moulds in which the casting space is bounded on its large sides by a pair of internally cooled rolls with parallel hori¬ zontal axes and rotating about these axes in. opposite directions, and on its small sides by closure plates (called side walls) made of refractory material which are * applied against the ends of the rolls. The rolls can also be replaced by cooled endless belts. In moulds of these types it is cohsid«red that it is preferable to orient the flows of the liquid metal primarily in the direction of the small sides of the casting space. An attempt is thus made, in particular/ to obtain a thermal homogenization of the metal so as to attenuate the variations in the thickness solidified along the perimeter of the mould. This thermal homogen¬ization and the stirring of the liquid melt which it requires are particularly crucial in the case of the casting o£ thin strips, because of the use of the refrac¬tory aide walls. In fact, if a forced renewal of the metal adjoining these side walls was not ensured, this metal would cool in an abnormally intense manner and undesirable metal solidifications would be seen to appear on the side walls. To obtain the desired homogenization, two-part nozzles (see document JP-A-60021171} are sometimes employed, especially in casting between rolls. The first part is made up of a cylindrical tube whose upper end is connected to an orifice made in the bottom of the dis¬tributor which forms the resezrve of liquid steel feeding the mould, an orifice which can be shut off at will by the operator, partially or completely, by virtue of a stopper or a slide gate system ensuring the control of the metal flow rate. The maximiwi flow rate of metal which can flow inside the nozzle depends on the section of this orifice. The second part, secured to the lower end of the above txibe, for example by screwing, is intended to be immersed in the liquid metal melt present in the mould. It is made up of a hollow member inside which the lower orifice of the above cylindrical tube opens out. The internal space of this hollow member has a general elongate shape in its end part and is oriented substantially perpendicularly to the tube. when the nozzle is in service the hollow member is placed parallel to the large sides of the mould and the liquid metal flows into the mould through two orifices made at each of the ends' of the elongate end part of the hollow member, which are called "nozzle openings". When a high flow rate of steel, of the order of for example 60 t/h, travels inside the nozzle, the speed of the metal in the tvibular part easily reaches several metres per second. In these conditions only a very partial filling of the section of the cylindrical part o£ the nozzle by the liquid metal is observed. This poor filling has a number of disadvantages. Firstly, owing to a "suction pump effect", it tends to promote the drawing in of external air by the porosities of the refractory and possible defects in the leaktightness of the connac-tion between the nozzle and the distributor, and this deteriorates the quality of the metal. Secondly, above all when the device shutting off the bottom of the distributor is only partially open, the flow of the metal is swirling and nonuniform. This results in a high instability of the metal streams leaving the nozzle openings, an instability which is further increased when an inert gas is blown into the nozzle to attenuate the first disadvantage which was referred to. It is thus possible to observe dissymmetries in the flows which are established on the right and left portions of the mould. This instability and this dissymmetry result in the appearance of waves inside the liquid metal melt in the mould, which continually vary the level of its surface, which is highly unfavourable for the uniformity of the solidifying of the product. These waves also cause the device ensuring the detection of the surface level and the control of its position to react without good cause; it tries to compensate what it takes to be variations in the average level of the metal by ordering rapid and con¬tinual alterations in the degree of opening of the stopper or of the slide gate. Furthermore, these incessant alterations will, in fact, aggravate the instabilities of the metal level. Finally, the high speeds of the liquid metal in the nozzle promote wear of the refractory materials of which it is made, in particu¬lar at the point of impact of the jet on the bottom of the horizontal hollow meisber. The aim of the invention, is to provide metal- • lurgiets with nozzles which ensure calmer and more unform conditions of flow of the metal into the mould than the nozzles usually employed in the continuous casting of metallurgical products. To this end the invention has as its subject a nozzle for introducing a liquid metal into a mould for continuous casting of metals, of the type comprising a tubular first part, one end of which is intended to be connected to a receptacle enclosing the said liquid metal/ and the other end of which opens into a hollow second part, at least one portion of the internal space of which is oriented svibstantially perpendicularly to the said tubular first part, the said portion comprising at each of its ends at least one orifice intended to open into the casting space of the said mould, characterized in that it comprises an obstacle placed in the path of the liquid metal inside the said txibular first part or in its extension, the said obstacle consisting of at least one perforated component intended to divert the metal from its preferential trajectory inside the nozzle. According to a first alternative form of the invention the said obstacle consists of at least one disc perforated with a multiplicity of holes. According to a second alternative form of the invention the said obstacle consists of a hollow com¬ponent provided with a bottom, entering the internal space of the said second part of the nozzle, the said hollow component comprising openings on its side wall. In one embodiment of the invention the internal space of the whole of the nozzle is in the general form of a T, As will have been understood, the invention consists in inserting into the path of the liquid metal an obstacle intended to oppose its natural flow by abruptly diverting this flow from its theoretical prefer¬ ential trajectory and by locally reducing the section of the space available for the metal to pass through. At an * equal metal flow rate, this has the effect of limiting the speed of the flow and of improving the filing of the internal space of the nozzle as a whole. The erratic variations in the conditions of the flow of the metal out of the nozzle are thus attenuated and the symmetry of the flows in the right and lest halves of the mould and the uniformity of these flows in time are markedly improved. Accordingly the present invention provides a nozzle for introducing a liquid metal into a mould for continuous casting of metals comprising a tubular first part with one end connected to a receptacle enclosing the said liquid metal, and the other end opening into a hollow second part in which at least one portion of the internal space is oriented substantially perpendicularly to the said tubular first part the said portion comprising at each of its ends at least one orifice for opening into the casting space of the said mould, characterized by an obstacle placed in the path of the liquid metal inside the said tubular first part or in its extension , the said obstacle consisting of at least one perforated component for diverting the metal firom its preferential trajectory inside the nozzle. The invention will be understood better on reading the description which follows, which is given with reference to the accompanying drawings in which; - Figure la which shows diagrammatically, seen in lengthwise section, a first alternative form of the invention, in which the obstacle consists of a stack of perforated discs, which are themselves shown in plan view in Figures lb, Ic and Id; - Figure 2 which shows diagrammatically, seen in lengthwise section, a second alternative form of the invention, in which the obstacle consists of a hollow component extending the tubular first part of the nozzle and directing the metal towards the side walls of the second part of the nozzle. In a first example of the embodiment of the invention, shown in Figures la-Id, the nozzle 1 is made up, as in the prior art referred to earlier, of two main parts made of a refractory material such as graphited alumina which are in this case assembled together by screwing the first into the second. The first part includes a cylindrical or substantially cylindrical tube 2, the internal space 3 of which forms the passageway for the liquid metal. This tube 2 is normally intended to be held vertically. Its upper part, not shown, is intended to be connected to a receptacle serving as storage container for liquid metal, such as a continuous casting distributor, in line with an orifice through which the liquid metal can flow at a flow rate which the operator regulates by means of a stopper or of a slide gate device. The lower end 4 of the txibe 2 comprises thread¬ing 5 on its outer wall and this threading 5 enables it to be assembled with the second part of the nozzle 1. This second part is made up of a. hollow member 6 which, in the example described and shown, has externally the ahape of an inverted T. The internal space 7 of the hollow member 6, itself also in the shape of an inverted T, thus comprises a cylindrical portion 8 extending the internal space 3 of the tube 2. The upper region of this cylindrical portion 8 comprises a widening 9 the wall o£ which is threaded, so as to make it possible to screw into it the lower end 4 of the tube 2. The cylindrical portion 8 opens into a tubular portion 10 which itself ia substantially perpendicular, of approximately circular, oval or rectangular section. Each end of this tubular portion 29 comprises an orifice 11, 11', called a "nozzle opening" through which the liquid metal can flow out of the nozzle. During casting these nozzle openings 10, 11 are intended to be held continually xinder the surface of the liquid metal filling the casting space. According to the invention the cylindrical portion 8 of the internal space 7 of the hollow member 6 comprises, inside the widening 9 and under the threading of its wall, a housing 12, in which a stack of three discs made of refractory material can be placed before the two parts 2, € of the nozzle 1 are assembled: an upper disc 13, an intermediate disc 14 and a lower disc 15. The respective dimensions of the housing 12 and of the discs 13, 14, 15 are chosen so that, after the nozzle 1 is assembled, the lower end of the tube 2 abuts against the upper disc 13. The upper disc 13 comprises a certain number of perforations 16 distributed over the portion of its surface intended to be situated vertically in line with the internal space 3 of the tube 2. The inter¬mediate disc 14 comprises a single perforation 17, for example square or circular in shape, with an opening which is at least ecjual to that of the internal space 3 of the tube 2. Its function is, in fact, that of a spacer used to separate the upper 13 and lower 15 discs. The latter itself also has a certain number of perfora¬tions 18 which may be different in number and in size from the perforations 16 of the upper disc 13. In order to obtain the required results, however, it is important that the perforrations 15 and 18 should be sxibstantially offset in relation to each other, so that a fraction of the liquid metal which is as small as possible is theo¬retically able to cross the obstacle consisting of the combination of the discs 13, 14, 15 without striking them. For better effectiveness of the obstacle it is also preferable that the upper disc 13 should preferably have no perforation in its middle, where the probability of the presence of liquid metal is the greatest, so as to alow down the casting jet as early as possible. In general, the total section of the orifices of a given disc must not be smaller than the section of the distributor exit orifice, in order to ensure that it will always be possible to cast with a maximum flow rate of metal which is as high as in the absence of an obstacle. Optionally, as is already Jcnown, the bottom 19 of the hollow member 6 is equipped with perforations 20, called "leakage holes**. The usual functions of these leakage holes 20 are to divert a proportion of the metal flows towards the lower part of the mould. This diver¬sion limits the flow rate and the exit speed of the metal at the nozzle openings 11, 11' and thus prevents the metal from violently striking the small sides of the mould and perturbing the solidification conditions therein. In the case of casting between rolls, this also makes it possible to avoid excessive deterioration of the refractory side walla. Furthermore, these leakage holes 20 ensure a uniform feed of hot metal in the low«r part of the casting space, particularly in line with the nozzle 1; here again, this tends to promote better control of the solidification conditions. The use of obstacles according to the invention makes it possible to obtain maxim\xm benefit from the advantages provided by the leakage holes 20, insofar as these leakage holes 20 are proportionally more effective the more uniform are the flows inside the nozzle 1 and in particular in the hollow member 6. In particular, this makes it possible to attenuate the preferential flow of the metal through the leakage holes 20 which are closest to the nozzle axis. By way of example, it may be proposed, in the case o£ the nozzle 1 in which the internal diameter of the tube 2 is 60 am and in which the nozzle openings 11, 11' of the hollow member have a circular section and a diameter of 30 mm, to employ an obstacle made up of three discs 13, 14, 15 of 100 mm external diameter and 25 mm thickness, which have the following characteristics: - the upper disc 13 has eight perforations 16 o£ 13 mm diameter, distributed in two rows of three perfora¬tions separated by a row of two perforations; - the intermediate disc 14 has a single per¬foration 17 which has a square section of 6 0 mm side or a circular section of 60 mm diameter; - the lower disc 15 has five perforations 18 of 19 mm diameter, namely a central perforation surrounded by four perforations arranged in a square. In this example, when liquid steel is cast, if the metal passes through the nozzle 1 at a flow rate of 60 t/h, it only partially fills the internal space of the tube 2 in the absence of an obstacle. However, the obstacle which has just been described is sufficient to slow down the flow of the liquid steel so as to reduce its speed to approximately 1 m/s and to obtain good filling of the tube 2 as well a metal exit speed which is steady and quite substantially uniform over the whole section of the nozzle openings 11, 11', with the same metal flow rate of 60 t/h. This provides a satisfactory stability of the metal level in the mould when the flow rate of the metal passing through the nozzle 1 is not altered. The discs must be made of a refractory material such as zirconia, compatible in any event with the nature of the metal which is cast, to prevent them from being excessively attacked chemically by the metal. Of course, the actual type of obstacle with discs which has just been described is merely an example which does not imply any limitation. It is possible to ' imagine,' in particular, employing only a single perfora¬ted disc if this is found to be sufficient to obtain an acceptable result in the usual casting conditions or, on the contrary, employing more than three discs to accen¬tuate the effect of slowing down the casting stream. Similarly, the presence of an intermediate disc 14 with a large single perforation 17, which therefore serves merely as a spacer between two discs 13, 15 with multiple small perforations, is not, strictly speaking, essential. However, it makes it possible to limit the wear on the lower disc 15 by avoiding an exclusive concentration of the metal flows on the solid regions of this disc which face the perforations in the upper disc 13. In a second example of embodiment of the inven¬tion, shown in Figure 2 (in which the members which are eoxomon with those in Figure la are marked using the seune reference signs), the obstacle inserted into the nozzle 1 consists of a tubular component 21 provided with a bottom 22 at one of its ends. At its open end this tubular component 21 has a shoulder 23 which can be inserted into the housing 12 arranged in the hollow member 6 and which contained the discs 13, 14, 15 in the preceding example of embodiment of the invention. On its side wall 24 the tubular component 21 has perforations 25, 26, 27 which allow the liquid metal to pass from the internal space 28 of the tubular component 21 to the internal space 7 of the hollow member 6, after having lost a great proportion of its potential energy. In the example shown in Figure 2 these perforations 25, 26, 27 are six in number, distributed at three levels over the height of the ttibular component 21 and are approximately aval in shape. They make it possible preferentially to iirect the liquid metal onto the side wall of the cylin-irical portion 8 of the internal space 7 of the hollow lember 6. In this way the impact of the metal against ;he side wall provides an energy absorption which is idded to that undergone inside the tubular component 21. similarly, to obtain a residence time of the metal in the ozzle 1 which is as long and uniform as possible, it is preferable that, as shown/ the direction of these per¬ forations should be perpendicular to the direction of the '{ nozzle openings 11, 11'. By way of example, a tubular component 21 in which the internal space 28 had a length of 84 mm, a diameter of 30 som and 10x20 mm perforations 25, 26, 27, would have an effect on the speed and the uniformity of the metal flows which is siibstantially comparable to that of the discs 13, 14, 15 of the obstacle described and shown in Figures la to Id, if it were inserted into an identical nozzle 1. The examples described above are, of course, not limiting. It would be possible, for example, to imagine inserting the obstacle in the actual interior of the tube 2 and not merely in its extension. It would also be possible to insert into the nozzle 1 a plurality of obstacles similar to those which have been described, or differing in their shape but capable of fulfilling the same functions. The invention is not limited in its application to the field of the continuous casting of flat products made of steel (slabs, thin slabs, thin strips) , even though it finds a prime application therein. It may be applied to many other examples of nozzles for continuous casting of any metals in all foirmats, in the case of which it is desired to obtain a slowing down of the flows providing better filling of the nozzle and, consequently, greater stability of the liquid metal flows Gmet-rt--"'"" therefrom. WE CLAIM: 1. A nozzle for introducing a liquid metal into a mould for continuous casting of metals, comprising a tubular first part (2) with one end connected to a receptacle enclosing the said liquid metal, and the other end (4) opening into a hollow second part (6) in which at least one portion (29) of the internal space (7) is oriented substantially perpendicularly to the said tubular first part (2), the said portion (29) comprising at each of its ends at least one orifice (10, 11) for opening into the casting space of the said mould, characterized by an obstacle placed in the path of the liquid metal inside the said tubular first part (2) or in its extension , the said obstacle consisting of at least one perforated component for diverting the metal fi-om its preferential trajectory inside the nozzle. 2. The nozzle according to claim 1, wherein the said obstacle consists of at least one disc perforated with a multiplicity of holes. 3. The nozzle according to claim 1, wherein the said obstacle consists of a plurality of discs (13, 15) perforated with a multiplicity of holes (16, 18) and separated fi-om each other by other discs (14) perforated with a single hole (17) having a cross sectional area approaching the internal cross sectional area of the said tubular first part (2). 4. The nozzle according to claim 1, wherein the said obstacle consists of a tubular component (21) provided with a bottom (22) for receiving the liquid metal the said tubular component (21) comprising perforations (25, 26, 27) in its side wall (24), the said perforations (25, 26, 27) permitting the metal to pass into the internal space (7) of the said second part (6) of the nozzle (1). 5. The nozzle according to claim 4 wherein the said perforations (25, 26,27) are oriented towards the inner wall of the said second part (6) of the nozzle (1). 6. The nozzle according to claims 1 to 5, wherein the said first part (2) comprises threading (5) on its outer wall for assembly with the said second part (6) of the nozzle (1) and the said obstacle is inserted into a housing (12) arranged in the internal wall of the said second part (6). 7. The nozzle according to claims 1 to 6, wherein the said portion (29) of the internal space (7) of the second part (6) which is oriented substantially perpendicularly to the first part (2) has an elongate shape, giving the internal space of the whole of the nozzle the general form of a T. 8. The nozzle according to claims 1 to 7, wherein the bottom (19) of the hollow member (6) comprises at least one leakage hole (20). 9. A nozzle for introducing a liquid metal into a mould for continuous casting of metals substantially as herein above described with reference to the accompanying drawings.

Documents:

1548-mas-1996 abstract.pdf

1548-mas-1996 claims.pdf

1548-mas-1996 correspondence others.pdf

1548-mas-1996 correspondence po.pdf

1548-mas-1996 description (complete).pdf

1548-mas-1996 drawings.pdf

1548-mas-1996 form-2.pdf

1548-mas-1996 form-26.pdf

1548-mas-1996 form-4.pdf

1548-mas-1996 form-6.pdf

1548-mas-1996 petition.pdf