METHOD FOR SEALING THE INGOT-MOULD/DUMMY-BAR ASSEMBLY IN A CONTINUOUS-CASTING PLANT, AND CORRESPONDING SEAL ELEMENT

Abstract: In a continuous-casting plant, a method of utilization of the sealing gasket between the dummy bar and the ingot mould envisages a seal element to be installed directly within the ingot mould outside of the continuous-casting plant. Said seal element (1) may be either in the form of a slightly deformable single sheet, or in the form of a rigid plate bearing along the entire edge a plurality of deformable detached parts (10) making up a continuous gasket.

Description: METHOD FOR SEALING THE INGOT-MOULD/DUMMY-BAR ASSEMBLY IN A CONTINUOUS-CASTING PLANT, AND CORRESPONDING SEAL ELEMENT Field of the invention The present invention refers to a method for sealing the ingot-mould/dummy-bar assembly in a continuous-casting plant, to the sealing gasket for implementing the method, and to the use of the said gasket in continuous casting. More in particular, the invention refers to a method in which the shaped gasket is set in the crystallizer off line, in conditions of total safety. State of the art In continuous-casting plants, the liquid metal is poured into an open-bottomed cooled crystallizer, or ingot mould, located above a line for extraction and further cooling. When coming into contact with the cooled internal walls of the ingot mould, the poured metal solidifies to form a shell, generally still containing liquid metal, which is extracted in a continuous way from the bottom of the ingot mould. The liquid metal contained in the shell solidifies completely along the casting line, after which the body thus produced is generally straightened and then cut into parts of a pre-set length. At the start of the casting operations, when the ingot mould is still completely empty, it is necessary to use means in order to prevent the molten metal from flowing as it is out of the ingot mould and in order to withhold it in the ingot mould until a shell having an adequate thickness and strength forms. For this purpose, a body is used, referred to as dummy bar, having a cross section slightly smaller than that of the ingot mould, so as to act as a provisional closure for the latter. The dummy bar is on the one side in contact with an underlying extraction assembly and, on the other, is equipped with means of hooking onto the body being formed by solidification of the liquid metal in the ingot mould. Bearing in mind that liquid metals have low viscosity (for example, the behaviour of liquid steel is altogether comparable to that of water), it is clearly indispensable to seal the space existing between the internal walls of the ingot mould and the dummy bar perfectly, in order to prevent leakage of the liquid metal and the consequent possibility of jamming the casting machine, of damaging it, or worse still, of jeopardizing the safety of the workers. The seal is made basically in two ways: either by putting the sealing material in the ingot mould after the dummy bar has been set in the operating position, or else by putting the sealing material as a gasket on the head of the dummy bar before the latter is inserted in the ingot mould. However, both these methods present important drawbacks. In fact, to put the sealing material in the ingot mould, either staff is required who must go to the mouth of the ingot mould underneath the tundish, and in any case underneath the equipment for supporting and moving the latter, or, as suggested, for example, by the published Japanese patent application JP 7-314099, an automatic machine is used, which sprays the sealing material inside the ingot mould. However, in the former case, the working conditions are very uncomfortable and dangerous, and, in the latter case, there is never the certainty that the layer of sealing material sprayed is perfectly intact and does not present dangerous fissures or gaps. In any case, the fact of using yet another machine increases the complexity and the cost of the process. If, instead, gaskets are used to be set directly on the head of the dummy bar, such as, for example, in the published Japanese patent application JP 8174160, or interposed plates, as in the European patent application No. 231 520, it is necessary to prevent the gasket from getting damaged by impact or tearing when the dummy bar is coming up to the ingot mould. Consequently, it is necessary to mount the gasket immediately before the ingot mould, and, to do this, the staff is obliged to work in the cooling chamber underneath the ingot mould to fix the gasket by hand on the head of the dummy bar, i.e., in working conditions that are even more uncomfortable and dangerous than those at the mouth of the ingot mould. The present invention has the purpose of overcoming these drawbacks by providing a simple and safe method for ensuring sealing of the ingot- mould/dummy-bar assembly. Summary of the invention The method according to the present invention is essentially based on the fact that a pre-formed seal element is used which is mounted inside the ingot mould, before insertion of the dummy bar in the latter, off the casting line used, preferably outside the casting plant. This latter solution is to be preferred on account of the major advantages that it offers, both in terms of execution times and on account of the conditions of absolute safety in which it is carried out. However, there may exist situations, for example in plants with an ingot mould mounted in stand-by alongside the casting line used, in which it may prove necessary to install the gasket within the casting plant, albeit outside the casting line being used. The aforesaid seal element is preferably equipped, along its entire edge, with a peripheral projecting raised part, roughly at right angles to the plane of the element and having a roughly wedge-shaped cross section tapered towards the free end, to be easily adapted to the head of the dummy bar when the latter is set inside the ingot mould, and to be gradually pressed between the dummy bar and the ingot mould in order to guarantee a perfect seal. In addition, the seal element may consist of a single sheet-like body made of plastic material, or of a plurality of parts consolidated by an associated rigid plate, for example made of metal. The seal element, which is made as a single body, may be provided with a central through hole, through which a consolidation element between the dummy bar and the casting body is connected to the dummy bar. The said consolidation element may be removable from the dummy bar and fixed on the latter with fast-clamping and fast-release means when the dummy bar is coming up towards the ingot mould, or else fixed on the said rigid plate, which in turn is connected with fast- clamping and fast-release means to the dummy bar. In the case of use of seal elements made up of a plurality of parts consolidated by a rigid plate, these parts are, for example, in the form of elongated bodies with a U-shaped section, the longitudinal cavity of which houses the edges of the said rigid consolidation plate. In any case, the seal element, whether as a single body or as a set of parts assembled on a rigid plate, has, in plan view, a shape similar to the horizontal section of the ingot mould with which it is to be employed, and the linear dimensions of the sides are slightly larger, for example between 0.1 and 4%, than the dimension of the corresponding side of the ingot mould, or of the diameter of the ingot mould in the case of ingot moulds having a circular cross section, so that the friction caused by the deformation of the seal element due to the difference in size will keep it in position inside the ingot mould. Preferably, the seal element, which is provided with a central through hole, may be equipped also with a plurality of cuts that start from the central hole, to facilitate passage of the element of consolidation with the cast body. In practice, a plurality of types of seal elements is prepared, one for each cross section of ingot mould. When a specific ingot mould is to be used, the appropriate seal element is chosen and, before insertion of the dummy bar, the element is installed inside the ingot mould, where it remains blocked, since, as has been mentioned previously, it has a cross section of slightly larger dimensions than the internal dimensions of the ingot mould. In the preferred case, whereby the operation is carried out outside the casting plant, the ingot mould provided with gasket can then be transported in due time to the continuous-casting machine and fixed on the latter. In any case, when the ingot mould equipped with gasket is in the casting line, the dummy bar, provided with the elements for hooking to the cast body, is made to go up towards the ingot mould and is pushed inside the latter. The engagement between the dummy bar, the internal walls of the ingot mould and the seal element favours the squeezing of the peripheral edge of the seal element against the ingot mould, in particular if the seal element is provided with a raised part projecting at right angles, thus affording a perfect seal. The elements for consolidation of the dummy bar with the cast body may be of any suitable type, for example of the so-called starting hook, or starting cage, or spiral type, may be integral with the dummy bar, or removable from the latter, or may be integral with the rigid plate, which in turn may be connected, in a removable way, with the dummy bar. The said consolidation elements or the said plate may be connected to the dummy bar by means of fast-clamping and fast-release elements, for example expansion rings, spring-action hooks, and the like. To speed up the formation of the first layer of solidified metal inside the ingot mould, and hence prevent the seal element from burning and so allowing liquid metal to leak out of the ingot mould, it is possible to add, in a way known per se, within the ingot mould, above the dummy bar provided with sealing gasket, cooling material, for example bits of scrap metal. Description of the drawings The present invention will now be described more precisely in regard to some preferred embodiments, illustrated, purely to provide non-limiting examples, in the annexed plates of drawings, in which: Figure 1 is a schematic view of a seal element according to the present invention; Figure 2 is a vertical section view of an ingot mould provided with a seal element, together with the head of the dummy bar ready to be pushed within the ingot mould; Figure 3 is a view similar to that of Figure 2, but with the dummy bar inserted in the ingot mould; Figure 4 is a schematic view of a seal element made up of a plurality of parts, associated to a rigid plate; Figure 5 shows two possible cross sections of one of the said plurality of parts making up a seal element. Figure 6 is a vertical section view of a further embodiment according to the invention of an ingot mould provided with a seal element, together with the head of the dummy bar ready to be pushed within the ingot mould; Figure 7 is a view similar to that of Figure 6, with the dummy bar inserted in the ingot mould; Figure 8 is a vertical section view of a further embodiment according to the invention of an ingot mould provided with a seal element, together with the head of the dummy bar ready to be pushed within the ingot mould; Figure 9 is a vertical section view of a further embodiment according to the invention of an ingot mould provided with a seal element, together with the head of the dummy bar inserted in the ingot mould; Figure 10 is a vertical section view of a further embodiment according to the invention of an ingot mould provided with a seal element, together with the head of the dummy bar inserted in the ingot mould; Detailed description of the invention In Figure 1 a schematic plan view is shown of a seal element 1 , provided with a projecting raised part 2 on its edge (shown hatched), with a central hole 3 and with cuts 4. As illustrated in Figure 2, in each specific ingot mould 5, when still outside the casting machine, a suitable seal element 1 is installed. In the Figure, the ingot mould is shown in line with the head of the dummy bar 7, which is in turn provided with means 6 for consolidation with the cast body. These consolidation means 6 may be integral with the dummy bar or else removable, in which case, means 11 (in themselves known) of fast clamping and fast release with the dummy bar are envisaged, e.g. hooks of different shapes and similar. Other embodiments of such consolidation means 6 and of fast clamping means 11 , and combinations thereof, are shown in figures 6 to 10. At the start of the casting operations, the head of the dummy bar 7 is introduced into the ingot mould 5, as shown in Figure 3, thus squeezing the edge 2 of the seal element 1 between the dummy bar and the internal walls of the ingot mould. In the position shown, the consolidation element 6 has forced the cuts 4 of Figure 1 to open so as to be able to pass through the hole 3, project within the ingot mould, and here subsequently hook up to the metal that will be cast into the ingot mould. The seal element 1 is advantageously made of semi-rigid and deformable material, such as plastics, thermoplastic resins and other materials having similar characteristics of strength and ductility. The seal element 1 can, in this latter case, also be reinforced by a stiffening plate 12, if necessary to achieve a better hold inside the ingot mould. As mentioned previously, the seal body 1 may have the shape of a plane sheet in a relatively rigid deformable material, preferably provided, on its edges, with a continuous raised part 2 having a roughly wedge-shaped section, projecting roughly at right angles from the plane of the said sheet. Alternatively, as shown in Figure 4, it is possible to use a rigid plate 8, for example made of metal, having, in plan view, a shape similar to the internal cross section of the ingot mould, but of smaller dimensions, this plate being equipped with means 6 for consolidation with the cast body and means (not shown) of hooking to the dummy bar. On the edges of the aforesaid rigid plate 8, are slot-mounted peripheral seal elements 10, which are made of plastic material and which form a continuous projecting part which protrudes beyond the edges of the rigid plate itself, so that the plate-plus-seal-elements ensemble assumes dimensions slightly larger than the internal dimensions of the ingot mould, in a way similar to what has been said regarding the seal element 1 in the form of a sheet, as described above. This ensemble is mounted, before insertion of the dummy bar, within the ingot mould, as has already been described for the element 1. Figure 5 shows two possible cross sections of the said seal element 10, one being roughly U-shaped, the other being similar to the first, but provided with a continuous raised part 2 having a roughly wedge-shaped cross section. The peripheral seal elements 10 can also be utilized in the embodiment shown in Figures 8 or 9. Figure 10 shows another variant of the cross section of the seal element, which in this case has the shape of a frame fitting only around the peripheral edge of the dummy bar head and leaving open the central part, to provide space for a hook 13 to couple with a correspondent hook 11 solidarily fixed to the rigid plate 8.

Claims: CLAIMS Method for the sealing of an ingot-mould/dummy-bar assembly in a continuous- casting plant characterised by the following steps: providing a pre-formed seal element, mounting said seal element inside the ingot mould when this is outside the casting line used, inserting the dummy bar in said seal element, anchoring said dummy bar to said seal element with clamping means. 2. Method according to Claim 1 , characterised in that it provides the step of mounting the seal element in the ingot mould when the latter is outside the casting plant. 3. Method according to Claim 1 , characterised in that it provides, for the said seal element, in plan view, a shape similar to the internal horizontal section of the ingot mould with which it will be used, and linear dimensions of the sides slightly larger than the dimensions of the corresponding sides of the ingot mould. 4. Method according to Claim 3, characterised in that it provides linear dimensions of the sides of the seal element larger than the dimensions of the corresponding sides of the ingot mould by an amount of between 0.1 and 4 %. 5. Method according to Claim 1 , characterised in that it provides a seal between the dummy bar and the ingot mould by means of a deformation of the edge of the said seal element forced between the internal walls of the ingot mould (5) and the dummy bar (7). 6. Method according to Claim 5, characterised in that it provides the said seal element (1 ) with a edge having a raised part (2) projecting roughly at right angles to the plane of the seal element and integral with it, the said projecting raised part having a cross section roughly triangular and being forced, in use, between the dummy bar and the internal walls of the ingot mould. 7. Seal element (1 ) for ensuring a seal between a dummy bar (7) and an ingot mould (5) in a continuous-casting plant, to be mounted within the ingot mould (5) when the latter is outside the casting plant, and consisting of relatively thin plane body having a shape, in plan view, correspondent to that of the ingot mould (5) in which it is inserted, having linear dimensions of the sides slightly greater than those of the corresponding inner sides of the ingot mould, said plane body being provided along its peripheral edge with a portion (2) projecting at substantially right angle to said plane body and integral with it, said projecting portion (2) having a substantially triangular cross section tapering toward the bulk of the dummy bar (7). 8. Seal element according to Claim 7, characterised in that it is provided with a central through hole (3) for enabling passage of hooking means (6) for anchoring said dummy bar (7) to the continuously cast body, from which a plurality of through cuts (4) start. 9. Seal element according to Claim 7, characterised in that it comprises a rigid plate (1 ) provided with consolidation means (11 ) with the dummy bar (7). 10. Seal element according to Claim 8, characterised in that it comprises a flexible plate (1 , 14) provided with consolidation means (11 ) with the dummy bar (7). 11. Seal element according to Claim 9 or 10, characterised in that it comprises a plurality of separate segments (10a, 10b, 10c, 10d) mounted along the edge of said plate. 12. Seal element according to Claim 11 , characterised in that said consolidation means (11 ) are releasably anchored to said dummy bar (7). 13. Seal element according to Claim 10, characterised in that said flexible plate (14) is provided with a reinforcing rigid plate (12). 14. Seal element (1 ) for ensuring a seal between a dummy bar (7) and an ingot mould (5) in a continuous-casting plant, to be mounted within the ingot mould (5) when the latter is outside the casting plant, and consisting of a relatively thin plane body (15) having a shape, in plan view, correspondent to that of the ingot mould (5) in which it is inserted, said plane body (15) being provided along its peripheral edge with a peripheral seal portion (10) mounted along the edge of said plane body (15) and having linear dimensions of the sides slightly greater than those of the corresponding inner sides of the ingot mould (5), in the mounted position. 15. Seal element according to Claim 14, characterised in that said peripheral seal portion is made of a plurality of separate segments (10a, 10b, 10c, 10d). 16. Use in a continuous-casting process of a seal element (1 ) according to any of claims 7 to 15, which is mounted within the ingot mould (5) before the dummy bar (7) is inserted into it.

Inventors: MAURIZIO MASSIMO, MERET MICHELE, POLONI ALFREDO, MAURIZIO, MASSIMO, MERET, MICHELE, POLONI, ALFREDO
Applicants: DANIELI OFF MECC, MAURIZIO MASSIMO, MERET MICHELE, POLONI ALFREDO, DANIELI & C. OFFICINE MECCANICHE S.P.A., MAURIZIO, MASSIMO, MERET, MICHELE, POLONI, ALFREDO
Application year: 2000
Main classification: B22D11
IPC codes: B22D11