MXPA00003038A - Mould pipe for a continuous casting mould for the continuous casting of steels, especially peritectic steels - Google Patents

Abstract

The invention relates to a mould pipe for a continuous casting mould for the continuous casting of steels, especially peritectic steels. The inventive pipe has a first longitudinal section (1) incorporating a predetermined position for the level (h) of liquid metal in the mould, and a second longitudinal section (2) following on from said first section. The first longitudinal section (1) comprises a heat-insulating layer (16), the dimensions of which are such that the heat resistance of the mould pipe (10) in the first longitudinal section (1) is greater than that in the second longitudinal section (2). The heat-insulating layer (16) fills an area from the outer surface (11) of the mould pipe (10) to a distance equivalent to at most 75%of the thickness of the mould pipe wall (dw) measured from said outer surface (11) of the mould pipe (10). By selecting the appropriate thickness profile for the heat-insulating layer in the direction of strand withdrawal (14), it is possible to set a given temperature profile on the inside of the mould pipe during a casting operation and optimise the growth of a strand shell.

Description

"PIPE PIPE FOR A CONTINUOUS PIPE FOR THE CONTINUOUS PIPE OF STEELS, PARTICULARLY PERIPHERAL STEELS" DESCRIPTION OF THE INVENTION The present invention relates to an ingot mold pipe for a continuous casting mold for the continuous casting of steels, particularly peritectic steels, according to the preamble of claim 1, and to a continuous cast ingot mold provided with such an ingot mold tube. The technique of continuous casting, in which by cooling a metal melt in the walls of a forming cavity of a continuous cast ingot mold, a crust of the cast bar is formed, progressively increasing in thickness, and continuously stretching a bar of an outlet opening of the continuous casting mold, as it is known, results in an application to peritectic steels, for example steels with a carbon content of 0.1-014%, to problems - which manifest themselves particularly in a poor quality SJJ surface of the bars manufactured. Such deficiencies in quality are undesirable, since further elaboration of the scales often results in deficiencies of unacceptable quality in the successive products. As is known, a cause of the aforementioned problems lies in a phase transition to which steels are subjected to a temperature below the solidification temperature and which leads to considerable shrinkage. In the continuous casting of peri-technical steels, this phase transition takes place during the initial solidification of a crust of the cast bar under conditions in which the crust of the cast strand in formation is still thin, has a low mechanical stability, and As a result of the phase transition, it forms an uneven surface, only punctually supported on the wall of the shaping cavity, with the result that already solidified bars have a porous or even surface layer on the surface. As is known, in the continuous casting of peri-steel steels, an improved quality of the surfaces of the cast bar can be achieved if the solidification of the crust of the cast bar is influenced in a zone of the lingo. continuous casting machine comprising the level of the liquid steel, by means of a reduction in the heat dissipation of the molten steel sheet or the crust of the cast bar. This decrease in the heat dissipation in the area of the initial solder is usually carried out with the help of continuous casting tongues which are provided with a thermal barrier on the face which gives the steel a longitudinal portion of the wall of the wall. conformation cavity. Said thermal barrier is dimensioned in such a way and the longitudinal portion is endowed with such measures that the thermal flux density results, on the one hand, reduced in the zone of the initial solidification but, on the other hand, is sufficiently large in the longitudinal portions subsequent to the thermal barrier to obtain, throughout the entire length of the strand in the shaping cavity, a sufficient growth of the strand of the strand. Several concepts are known for providing the walls -of the forming cavity of a continuous cast ingot mold, in the area of a partial section comprising the position -of the level of the liquid steel that is established during the casting process, of a barrier thermal on the delimiting surface of the shaping cavity. From the summary of JP 1-224 142 A there is known a leak intended for the manufacture of peritectic steels, whose wall of the shaping cavity consists of a tubular body with a cylindrical insert, disposed on the inlet side, steel or other materials that have a higher thermal resistance than the material constituting the tubular body. This mold has the disadvantage that the constituent insert of the thermal barrier is prone to wear and that particular measures are required., enhancing the production of the ingot mold, to counteract formations of cracks or deformations of the wall of the forming cavity as a result of the thermal stresses during the casting process. An alternative concept for the constitution of a thermal barrier is disclosed in the summary of JP 1-170 550 A in the example of a plate mold intended for the manufacture of peritectic steel slabs. The surfaces that give to the cavity of conformation of the side walls-manufactured of copper of this mold have, in a zone -which comprises the position of the level of the liquid steel, drills that are selectively filled with nickel, stainless steel or a ceramic material appropriate. This alternative concept suffers from the drawback that - apart from the propensity to - wear the fillings of the drills - for reasons of manufacturing technique is not applicable to tubular ingot molds for - small bar formats, for example palanqui formats - - lias, since the internal faces of the ingot mold tubes are only insufficiently accessible for an adequate machining. From the summary of JP02-006 038 A is known a 1 in leak intended for the casting of peritectic steels, whose walls of the forming cavity are made of copper and -presentan, on the face furthest away from the forming cavity , slots for cooling water. In the grooves for cooling water they are housed, in an area comprising the -position of the level of the liquid steel and with periodic separations of 5-20 mm, metals or ceramic materials with a thermal conductivity lower than that of copper. In order to create a thermal barrier with a predetermined thermal resistance according to this concept, it is necessary that the housed materials extend over a relatively large depth in the wall of the shaping cavity. The realization of such a thermal barrier is expensive in terms of manufacturing technique, since in a plurality of places in the wall of the shaping cavity it is necessary to accommodate suitable materials in a relatively deep manner. Accordingly, the purpose of the present invention is to contribute to the solution of said problems-and to provide for this purpose an ingot mold tube that is endowed with a thermal barrier, capable of being obtained with -simplified means of technique. of manufacture, which is arranged in the position of the level of the liquid steel and is protected against wear, as well as a corresponding mold-continuous casting provided with such an ingot mold tube. This purpose is achieved by means of an ingot tube ra which is characterized by all of the features of claim 1, and by a continuous cast ingot mold with the features of claim 10. The ingot mold tube according to the invention has a -primera longitudinal portion, which comprises a predetermined position of the level of the liquid steel, and a second longitudinal portion, subsequent to the first, the first longitudinal portion being provided with a thermally insulating layer that is dimensioned in such a way that the thermal resistance -of the tube of ingot mold in the first longitudinal portion pre-I found a higher value than in the second longitudinal portion. The ingot mold is characterized in that the thermally insulating layer occupies a zone between the exterior surface of the ingot mold tube and a distance of maximum 75% of the wall thickness of the 1-length pipe, measured from the exterior surface of the ingot mold pipe. The thermally insulating layer of the ingot mold tube according to the invention is arranged on the outside of the mold tube, or close to it, and does not reach the inner surface of the tube. Accordingly, the ingot mold tube can be manufactured from a tubular body, capable of being machined on the outside to be equipped with the thermally insulating layer. The machining can be carried out with conventional methods even in the case of tubular bodies that are suitable for obtaining ingot mold tubes with small internal diameter and which, because of their geometrical dimensions, they do not allow a mechanization by their internal face, or only in a very expensive way. During the casting process, the thermally insulating layer is occupied, in the region of the first longitudinal portion, by an increase in the temperature on the inside face of the ingot mold tube. Because the distance of the thermally insulating layer from the inner surface of the hoist tube is at least 25% of the wall thickness of the hoist tube, the ingot tube wear during the casting process is consequently The thermal stress and the marble stress of the material in the zone of the first longitudinal portion is reduced, in comparison with an ingot mold tube which is provided with a thermally insulating layer of equal thickness in the interior part of the ingot mold tube. In the ingot mold pipe according to the invention, it is possible, by suitable dimensioning of the thickness profile of the thermally insulating layer, to adjust in a defined manner the temperature variation that is established during the -deck process on the inner surface of the ingot mold tube. , in order to objectively influence the growth of a crust of the cast bar in the area of the first longitudinal portion. This degree of freedom is used, in the ingot mold according to the invention, to optimize it for the production of peritectic steel bars. In order to optimize the quality of the peritectic steel casted products, the temperature on the inner surface of the ingot mold tube must be, on the one hand, during the casting process, in the region of the first longitudinal portion, as high as possible . With this, the initial solidification of the steel melt begins in a delayed manner at a distance as large as possible from the level of the liquid steel, with the effect that the ferrostatic pressure of the melt, which increases in function of the increasing distance from the liquid steel level, more strongly counteracts a local separation, stimulated by the transition of peritectic facies, from the crust of the cast bar in formation - with respect to the inner surface of the ingot mold tube and - thereby favoring the shaping of a smooth surface of the cast bar. On the other hand, during the casting process the temprature on the inner surface of the ingot mold tube can not be of any value, since the properties of the ingot tube material act in a limiting manner. Thus, for example, as is known, an ingot mold pipe manufactured after cooling, at a temperature above a critical temperature of 450 ° C, has a so-called softening temperature, an unacceptably short life. Accordingly, in an advantageous embodiment of the ingot mold tube according to the invention, the thickness of the thermally insulating layer is dimensioned in such a way that in the casting process the temperature on the inside surface of the ingot mold tube does not exceed a predetermined temperature U. In a further embodiment of the ingot mold tube according to the invention, the outer surface of the ingot mold tube is formed, in the boundary between the longitudinal portions, in a step-free manner. This form of realization is particularly suitable for use in ingot molds, with cooling by a water jacket on the outside of the ingot mold tube. As in such ingot molds, the water jacket is usually only a few mm thick and its thickness must be precisely controlled along the ingot mold tube, a step-free configuration of the transition between the two longitudinal portions enables construction in particular simple cooling by water jacket. In a further development of the ingot mold tube according to the invention, the thermally insulating layer is housed in a tubular body made of metal or a metal alloy. Favorable thermal and mechanical properties of the ingot mold tube are determined if the tubular body is made of copper or a copper alloy and the thermally insulating layer is made of a metal, for example nickel or chromium. These materials are well adapted to each other, in terms of their coefficient of dilation, so that a layer of nickel or chromium applied to a copper surface is characterized by a good adhesion and by a high resistance to wear. Further embodiments of the ingot mold tube according to the invention are thermotechnically designed in such a way as to cool the exterior surface of the ingot mold tube by means of a cooling medium, than the temperature of the inner surface in the region of the mold. The first longitudinal portion reaches at most a predetermined critical temperature and is maintained at least in a partial section of the first longitudinal portion practically constant. In this way, the initial solidification of the crust of the cast bar can be retarded to a particularly large distance from the level of the liquid steel and a particularly smooth surface of the cast bar can be achieved once the peritectic phase transition has passed. In order to achieve a temperature profile as constant as possible in the longitudinal direction, the thickness a of the thermally insulating layer must increase, at least in a section between the position of the liquid steel level and the second longitudinal portion, in the direction towards said according to the longitudinal portion. Next, various ways of realizing the ingot mold tube according to the invention will be described, with reference to the attached schematic drawings, in which: Fig. 1A is an elevation view of an example of the ingot mold tube according to the invention; Fig. 1B is a cross-sectional view according to line I-I in Fig. 1A; Fig. 1C is a cross-sectional view according to line 11-11 in Fig. 1A; Fig. 2A is a longitudinal sectional view according to the line 111-111 in Fig. 1C, for a given profile of thickness of the thermally insulating layer; Fig. 2B is a longitudinal sectional view analogous to Fig. 2A, but for another thickness profile of the thermally insulating layer; Fig. 3 shows trajectories of the thickness a of a thermally insulating layer according to Fig. 2A, as a function of the wall thickness dw of the ingot mold tube, for a predetermined wall temperature; and Fig. 4 shows a dimensioning of a thermally insulating layer as a function of the wall thickness dw of the ingot mold tube, for a predetermined profile of the temperature of pj? net. FIG. 1A shows an example, illustrated in elevation view, of the ingot mold tube 10 according to the invention, with a shaping cavity 20, a pouring opening 12 and an extraction opening 13 for a rod (not shown). The direction -extraction of the bar, provided in the casting process, is indicated by an arrow 14. The ingot tube 10 comprised of a first longitudinal portion 1 and a second longitudinal portion 2, including the longitudinal portion 1, a position h of the level of the liquid steel, provided in the casting process, and the longitudinal portion 2 being arranged following the longitudinal portion 1 in the direction 14 of extraction of the -bar. The ingot tube 10 consists of a tubular body 15 with a thermally insulating layer 16 in the area of the longitudinal portion 1. FIGS. 1B and 1C show cross sections of the ingot mold tube 10: Fig. 1B a cross section in the plane II indicated in Fig. 1A in the area of the longitudinal long portion 1, Fig. 1C a cross section in the plane 11-11 indicated in Fig. 1A in the area of the longitudinal portion 2.

As can be seen from Figs. 1A-C, the thermally insulating layer 16 is disposed on the outer part 11 of the tubular body 15. The forming cavity 20 has, for example, a square cross section with rounded corners. This choice is arbitrary. The ingot mold tube according to the invention can be provided with any desired cross-sectional shape which is common in the practice of continuous casting. Figs. 2A and 2B represent longitudinal sections according to the line 111-111 in FIGS. 1B and 1C, respectively, and -characterize two different embodiments of the ingot mold tube 10 according to the invention, which differ in the confi guration of the profile of the mold. thickness of the thermally insulating layer 16 in the longitudinal direction of the ingot mold tube. In both cases the thermally insulating layer 16 is housed in a scoring on the outside of the tubular body 15. In these examples the outer surface 11 of the ingot mold tube 10 is free of steps at the edges of the longitudinal portion 1. Tubular body conveniently consists of copper or a copper alloy. As materials for the constitution of the thermally insulating layer, metals such as nickel or chromium conveniently come into consideration, which are capable of being applied to the tubular body 15 by conventional means, for example, plating or electrochemical processes. However, other materials, for example ceramic materials, can also be used for the constitution of the thermally insulating layer, provided that they have a lower thermal conductivity than the tubular body 15 and are suitable in terms of their adhesion properties. and its resistance to openness. The embodiment illustrated in FIG. 2A of the ingot mold pipe 10 according to the invention is characterized in that the thermally insulating layer 16 has, in the region between the position h of the level of the liquid steel and its boundary border, the portion longitudinal 2, an essentially constant thickness, designated in Fig. 2A with d. With this geometry, the temperature on the inner surface of the ingot mold tube-10, during the casting process and with uniform cooling of the outer surface 11 of the ingot mold tube 10, would decrease from a maximum temperature point located at the level position h of the liquid steel, in the direction 14 of extraction of the cast bar, since a crust of the bar that is formed in the area of the longitudinal portion next to the inner surface-25 of the ingot mold tube 10 has an increasing thickness in the direction 14 of extraction of the bar and care is taken that the thermal fl ow between the surfaces 25 and 11 of the ingot mold tube-10 decreases along the direction 14 of extraction of the bar. By a corresponding variation in the thickness of the thermally insulating layer 16 in the direction 14 of extraction of the bar, the temperature profile that is established on the inner surface 25 of the ingot mold tube 10 can be objectively modified in order to optimize the growth of the -coat of the cast bar. The embodiment illustrated in FIG. 2B of the ingot mold tube 10 according to the invention is characterized in that the thermally insulating layer 16 increases, in the region between the position of the level of the liquid steel and its edge bordering the longitudinal portion 2. , cuneiform from a thickness gives a thickness b. The thicknesses d_ and b can be chosen, for example, in relation to the wall thickness -dw of the ingot mold tube 10, in such a way that the temperature path on the inner surface 25 of the ingot mold tube 10 is substantially constant in the direction 14. of extraction of the bar and reach a predetermined value. The detailed temperature path is naturally correlated with the growth of the crust of the strand cast on the surface 25. The tubular body 15 is usually designed for use at a temperature below a critical maximum temperature T " The ingot mold tube 10 can be dimensioned thermotechnically in the following manner for the continuous casting of steel, assuming cooling of the outer surface by application of a cooling medium. In order that the temperature on the inner surface 25 of the ingot mold tube 10 does not exceed a predetermined critical temperature U, the thickness d of the thermally insulating layer 16 should be dimensioned, at the position h of the level of the liquid steel, according to the formula * w? w [iotL + ts - 11TK] [1-f] a [Ts-t?] [l-f] where? w: Thermal conductivity of the ingot mold tube 10 in the second longitudinal portion 2; f: Ratio? w /? ¿, where? means the thermal conductivity of the thermally insulating layer 16; T Critical temperature; T_: Temperature of the steel on the inner surface 25 of the ingot mold bo 10; L: Temperature of the cooling medium; or. : Thermal transmission coefficient for the transmission between the cooling medium and the thermally insulating layer 16. FIG. 3 illustrates d-dMflJ. according to equation (1) -graphically as a function of wall thickness dw for the two parameters f = 4 and f * 10, assuming U = 450 ^ 0, T? = 14805C and the following representative values for cooling -by water is a characteristic experience value for copper. The two parameters f = 4 and f = 10 are, for example, representative for an ingot mold tube 10 with a tubular body 15 of copper and a thermally insulating jacket 16 of nickel (f = 4) or steel (f = 10). As can be seen in Fig. 3, the ratio dMA "/ dw decreases as the wall thickness dw increases in the ingot mold tube 10. The smaller the dw thickness of the ingot mold tube 10, the greater the the thickness of the thermally insulating layer in the total thickness dw of the pipe -of ingot mold 10, in order to raise the temperature in the inner surface 25 of the ingot mold tube 10 in the longitudinal portion 1 up to the critical temperature U, in the given example U = 450QC. In addition MA? / Dw is both greater, for a predetermined p dw network thickness, the smaller is f, that is, the greater the thermal conductivity of the thermally insulating layer. According to experience, the wall thickness dw of the ingot mold tube 10 should typically be about 10% of the length of the side of a cross section of the shaping cavity 20. If the ingot tube 10 is sized for small billets with a side length of the cross section of approximately 10 cm, for f = 4 the thickness ratio MA? / dw will be approximately 75%. For MA "/ dw 2 75% and f < 4 the manufacture of the ingot mold tube 10 from a solid tubular body 15 becomes problematical, since the mechanical stability of the tubular body 15 is excessively diminished by the realization of the notch 16 intended for thermally receiving the layer. insulation 16 on the outside 11 of the tubular body 15. Furthermore, as the ratio MA? / dw increases the cost for the embodiment of the thermally insulating layer 16 increases, particularly in manufacturing processes in which the thermally insulating layer 16 is constituted by continuous supply of thin layers of an appropriate material. Accordingly, for the embodiment of the thermally insulating layer 16 is preferable, in addition to the condition dMA? / Dw < 75%, the range of pja rametro f ^. In Fig. 4 it is indicated, for the ingot mold tube 10 and for the case that the thickness of the thermally insulating layer 16 increases, in the direction 14 of extraction of the bar, from the thickness _d in the position of the level of the liquid steel up to the thickness b according to a profile of thickness determined in such a way that during the casting process the temperature in the inner surface 25 is constant along the thickness profile, as the ratio b / dw varies depending on the of the wall thickness d ... Based on equation (1) and Fig. 4-the b / dw and d / dw ratios can be determined for the case that during the casting process is carried out along the profile of thickness the critical temperature T A comparison with Fig. 3 provides the corresponding values for the special case T? = 450í >; C The curve path illustrated in Fig. 4 is not dependent on f. The length of the ingot tube 10 is typically 80-100 cm. The length of the longitudinal portion I is preferably of the order of 10-15 cm, the position of the level of the liquid steel preferably being located in the upper quarter of the longitudinal portion 1. In the above-mentioned embodiment examples the layer The thermally insulating 16 is always housed in a recess of the tubular body 15 in such a way that the outer surface 11 of the ingot mold tube 10 is configured free of steps. Within the scope of the invention, it could also be preferred to provide a housing for the thermally insulating layer 16 in a recess or in a step-free configuration of the outer surface 11. The surfaces 11 and 25 of the ingot mold tube according to FIG. invention could also be provided with coatings of suitable materials. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (11)

1. R E I V I N D I C A C I O N S
2. Having described the invention as above, the content of the following claims is claimed as property. 1.- Ingot tube for a casting mold with tínua for the continuous casting of steels, particularly peritectic steels, with a first longitudinal portion that includes a predetermined position (h) of the level of the liquid steel, and a second longitudinal portion subsequent to the first, comprising the first longitudinal portion, at or in the prosimianity of the exterior face of the ingot mold tube, at least one thermally insulating zone and being constructed in such a way that the thermal resistance of the ingot mold tube present in the first -ra longitudinal portion a greater value than in the second longitudinal portion, charrized in that the thermally insulating area consists of a thermally insulating layer that fills a -zone between the exterior surface of the ingot mold tube and a -distance of maximum 75% of the thickness of wall (dU of the pipe-bundle, measured from the exterior surface of the ingot mold tube 2.- Ingot tube according to the claim ication 1, charrized in that the exterior surface of the ingot tube ex; It is configured free of steps in the boundary between the longitudinal portions.
3. 3. - Ingot tube according to one of the claims 1 or 2, charrized in that the thickness (d) of the thermally insulating layer is dimensioned in such a way that during the casting process the temperature on the inner surface of the de-ingot tube does not exceed a predetermined critical temperature - V
4. 4.- Ingot tube according to one of the claims 1-3, charrized in that the thermally insulating layer is located in a tubular body made of metal or a metal alloy.
5. 5. Ingot tube according to claim 4, charrized in that the ingot tube is designed thermotechnically for a continuous casting with cooling of the outer surface by application of a cooling medium, -dimensioning the thickness d of the thermally insulating layer in the position (h) of the liquid steel level according to the formula ? ? w [iotL + ts - 11TK] d < [1-f] a [Ts-T?] [1-f] where d? : Wall thickness of the ingot mold tube in the first longitudinal portion; ",: Thermal conductivity of the ingot mold tube in the longitudinal portion according to; f: Relationship > where . , means the thermal conductivity of the thermally insulating layer; U: Critical temperature; T? : Temperature of the steel on the inner surface of the ingot mold tube; T.: Temperature of the cooling medium; s .: Thermal transmission coefficient for the transmission between the cooling medium and the thermally insulating layer.
6. 6. Ingot tube according to claim 5, charrized in that f = 4.
7. 7. Ingot tube according to one of claims 5 or 6, charrized in that the thickness (d, b) of the thermally insulating layer increases, in a section between the position (h) of the level of the liquid steel and the second longitudinal portion , in -direction towards the second longitudinal portion.
8. 8. Ingot tube according to claim 7, sided because the thickness increase of the thermally insulating layer is dimensioned in such a way that the temperature on the inside surface of the ingot mold tube is prcally constant during the casting process. in the area of the aforementioned section.
9. 9. Ingot tube according to one of claims 4-8, charrized in that the thermally insulating layer is made of a metal, for example nickel or chrome, and the tubular body is made of copper or an alloy of copper.
10. 10. - Continuous cast ingot for the continuous casting of steels, particularly peritectic steels, provided with an ingot mold tube according to one of the claims 1-9.
11. 11.- Continuous cast ingot according to claim 10, charrized in that a device is provided for the application of a cooling medium to the exterior surface of the ingot mold tube, for example a cooling by water neck.