Title of Invention

REFRACTORY PLATE(S) FOR LATERAL CONTAINMENT OF MOLTEN METAL IN AN APPARATUS FOR THE CONTINUOUS CASTING OF THIN, FLAT METALLIC PRODUCTS AND PROCESS THEREOF

Abstract

The present invention discloses refractory plate(s) for the lateral containment of molten metal in an apparatus for the continuous casting of thin, flat metallic products, said refractory plate(s) comprising: one or more insert(s) of ceramic material, such as herein described, having substantially triangular shape, wherein, externally to said insert (s) a first casting of a silica - alumina refractory material, such as herein described, containing ceramic fibres is provided; internally to said insert(s) and being bound peripherally by said insert(s), a second casting of a silica-alumina refractory material having a high content of zirconia, such as herein described, is provided, on the back of said insert (s) and said first casting and said second casting, there is provided a third casting of a SiC-based thixotropic material for supporting the said insert(s), said first casting and said second casting; and plurality of joints of ceramic fibres material, such as herein described, are provided at the contacting surface (s) between said insert (s) and at least one of said first, second and third castings, for thermal expansion; the arrangement being such that said second casting is disposed on said third casting such that said second casting is located at the central portion of the plate(s) defined by said insert(s).

Full Text

- 1A - DESCRIPTION The present invention relates to refractory plates for the lateral containment of molten metal, in an apparatus for the continuous casting of thin, flat metallic products. Presently, such plates are produced according to a known technique including the following steps: - casting a material having a high contents of SiC; - creating areas destined for the containment of the inserts; - firing at a high temperature (1250°C) of the plate thus obtained; — inserting, by means of a refractory cement having a high contents of ZrO2 (or SiC) , the inserts of composite ceramic material (constituted, for example, of BN/Sialon or of BN/SiC/ZrO2) ; — casting a silica-alumina refractory material having a high contents of ZrO2 on the preformed plate of the previous casting; and - firing at a low temperature (about 400°C) of the plate so constituted. Such technique for the production of refractory plates having ceramic material inserts, shows the disadvantage of being time-consuming and awkward Moreover, it has the inconvenience of not allowing the achievement of plates with a good planarity caused by the fact that the inserts have level differences each other, even if these have a reduced value. Another drawback of such technique consists in that, -2- owing to the dimensional contraction of the casting and of the cement employed for the fastening of said inserts on the casting, some times there occur fissures between the inserts and adjacent parts of the plate These fissures lead to possible infiltrations of molten metal with the consequent build-up of solid metal on the surface of the same Such solid metal becomes the nucleus for the growth of solid steel crusts that endanger the whole casting process. Thus, the aim of the present invention is to provide improved refractory plates having inserts of ceramic material that solve the abovementioned problems of reduced planarity, of a time-consuming and difficult production of the same, and of the generation of fissures in the areas between inserts and refractory castings. Another aim of the present invention is to provide low-cost improved refractory plates with ceramic material inserts. A further object of the present invention is to provide a process for the production of such improved refractory plates. Accordingly, the present invention provides refractory plate (s) for the lateral containment of molten metal in an apparatus for the continuous casting of thin, flat metallic products, said refractory plate(s) comprising: one or more insert(s) of ceramic material, such as herein described, having substantially triangular shape, wherein, externally to said insert(s) a first casting of a silica - alumina refractory material, such as herein described, containing ceramic fibres is provided; internally to said insert(s) and being bound peripherally by said insert(s), a second casting of a silica-alumina refractory material having a high content of zirconia, such as herein described, is provided; on the back of said insert (s) and said first casting and said second casting, there is provided a third casting of a SiC-based thixotropic material for supporting the said insert(s), said first casting and said second casting, and -3- plurality of joints of ceramic fibres material, such as herein described, are provided at the contacting surface (s) between said insert(s) and at least one of said first, second and third castings, for thermal expansion; the arrangement being such that said second casting is disposed on said third casting such that said second casting is located at the central portion of the plate(s) defined by said insert(s). Moreover, the present invention provides a process for the production of refractory plates with ceramic inserts, characterised in that it comprises the following steps : — positioning and optimised coupling, by means of gluing, of at least one insert of ceramic material on the bottom of a mould; — positioning with an optimised coupling of a plurality of joints constituted in ceramic fibres, on the peripheral walls of said at least one insert of ceramic material; — carrying out of a first casting of a refractory material, substantially constituted of a mixture of silica-alumina and ceramic fibres, at the external part of said at least one ceramic insert; — carrying out of a second casting of a silica-alumina refractory material having a high contents of ZrO2, at the central part of the plate and internally bounded by said at least one ceramic insert; — carrying out of a third casting of a refractory thixotropic material with a high contents of SiC, above said at least one ceramic insert, with respect to said first casting of refractory material and said second casting of refractory material having a high contents of ZrO2, — -4- - removing the plate thus constituted from said mould, after a time of at least 24 hours, - thermal treating the plate at 110°C for a period of time of at least 24 hours, and - firing at low temperature said plate at least at 400°C for a time period of at least 1 hour The present invention will be now better shown by the disclosure of a preferred embodiment thereof, given as an exemplary and non-limitative embodiment, with reference to the accompanying drawings, wherein Fig 1 is a perspective view that shows schematically an apparatus for the continuous casting of thin, flat products, according to the present invention, Fig. 2 is a perspective view that shows partially a first embodiment of the plate, according to the invention, Fig 3 is a cross sectional view of the plate of Fig. 2, taken along line A-A; Fig 4 is a perspective view that shows partially a second embodiment of the plate according to the invention; and Fig. 5 is a cross sectional view of the plate of Fig. 4 , taken along line A-A. With reference now to Fig 1, it shows schematically an apparatus for the continuous casting of flat, thin products Conventionally, the apparatus Comprises a pair of counter-rotating rolls 1 and 2, and with their rotation axes spaced by a distance greater than the sum of their radiuses. At both the lateral faces of said rolls 1 and 2 there are arranged two flat walls 3 and 4 which have respective refractory plates 5 (better shown hereinafter) for the lateral containment of molten metal 6 cast between the rolls 1 and 2 The arrangement is such to obtain a flat product 7 following the rotation of the rolls 1 and 2 -5- With reference now to Fig. 2, it shows a perspective view that illustrates partially the plate according to the invention. The plate 5 is constituted of a plurality of inserts 8 of a ceramic material arranged along the contacting arc between the edges of the rolls 1, 2 (schematically shown by means of the lines A-A) and the surface of the plate. The arrangement of the inserts 8 is such so that they assume a "Y"-shape on the plate 5. At the side portion of the plate and externally to the inserts 8 , a first casting 9 of a silica-alumina refractory material containing ceramic fibres is provided. Such a compound has an extremely low thermal conductivity, avoiding thus the dispersion of heat towards the exterior On the other hand, at the upper central portion of the plate, bounded peripherally by the inserts 8, there is obtained a second casting 10 of a silica-alumina refractory material having a high contents of Zircoma (ZrO2) , that has a high resistance to the chemical attack of the molten metal and a low wettability and, obviously, a high degree of refractoriness. At the peripheral surfaces of said inserts 8, there are arranged joints 11 for the thermal expansion (having the shape of elongated elements) constituted of highly refractory ceramic fibres, arranged for compensating the different thermal expansion between the inserts 8 and the adjacent castings 9 and 10, respectively, thus avoiding the formation of possible spaces or fissures that might constitute nuclei of cooled metal, with the consequences disclosed hereinabove On the back of the inserts 8 and the castings 9 and 10, is provided a third casting 12 of a thixotropic material having a high contents of SiC, providing the support for the abovementioned inserts 8 and the castings 9 and 10, respectively by covering them on their back and entirely Said casting 12 of a thixotropic material has a -6- high thermal conductivity and high mechanical characteristics. With reference to Fig. 3, it shows a cross section of the plate, taken along the line A-A of Fig. 2. As one can see, the third casting 12 of material having a high contents of SiC, constitutes the support both for the inserts 8 and for the castings 9 and 10, respectively. With reference now to Figs 4 and 5, they show a perspective view a cross sectional view along the line A-A, respectively, of a second embodiment of the present invention For sake of simplicity, the disclosure of parts having the same reference numerals of the former embodiment will be omitted because of the same constitution and, therefore, already previously described. As it is clear, in this embodiment, the plate has a single insert 8 in a ceramic material and in the shape of substantially a triangle Herebelow two examples will be given of the embodiments of a plate, according to the present invention EXAMPLE 1 Refractory plates have been obtained by means of a casting material and inserts in a ceramic material, having the following features: a)Inserts constituted of a ceramic composite material _ The ceramic inserts have the following composition, expressed in percentage in weight with respect to the total weight of the mixture - ZrO2 50% - BN 45% - SiC 5% b)First casting of a silica-alumina refractory material constituted of ceramic fibres A material has been utilised substantially constituted of the following -7- compounds, expressed in percentage in weight with respect to the total weight of the mixture - A12O, 45% - SiO2 33% - Fe2O3 3, 5% resulting in a material with the following features: - refractoriness = 1300°C - thermal conductivity at 1000°C = 0,23 W/m K c)Second casting of a silica-alumina material having a high contents of Zircoma. A material with a high contents of Zircoma has been utilised, substantially constituted of the following compounds, expressed in percentage in weight with respect to the total weight of the mixture: - ZrO2 43% - Al2O_ 28% - SiO2 24% Thus, it was obtained a material with a refractoriness higher than 1650°C and with an excellent resistance to the chemical attack by the molten metal and a low wettability. d)Third casting of a refractory material with a high contents of SiC. It was utilised a material with a high contents of SiC and substantially constituted of the following compounds, expressed as a percentage in weight with respect to the total weight of the mixture - Al2O3 85% - SiO2 4,5% - SiC 85% Thus, a material with the following characteristics has been obtained - refractoriness > 1600°C - thermal conductivity at 1000°C > 5 W/m K - tensile strength > 800 kg/cm Moreover, joints for the thermal expansion have been inserted between the inserts and the castings, constituted essentially of the following compound, -8- expressed as a percentage in weight with respect to the total weight of the mixture: - Al2O3 8 5% - SiO, 5% Refractory plates have been obtained by means of casting a refractory material constituted as in the former example and inserts of a ceramic material, the inserts having the following composition, expressed in percentage in weight with respect to the total weight of the mixture. - BN 30% - SiAlON (Oxinitride of silicon and aluminium) 70% Consequently, with the plates constituted according to the above examples, several castings of INOX 304 steel have been accomplished, and more than 1000 m of a thin band having a thickness of 2 5 mm and width of 8 00 mm were achieved Furthermore, the wear detected of the ceramic inserts has been lower than 3 mm/km. Work tests confirmed the effectiveness of the new assembly that has given origin to neglectable undesired solidifications. As a matter of fact, with respect to the embodiments of plates according to the prior art, in which the sliding inserts are bound with a refractory cement to the underlying plate, the present embodiment allows to obtain a monolithic composite plate in which all the components are assembled each other with continuity thanks to the formation of chemical bonds having high mechanical charactaricstcs. In this way there is avoided the possibility of occurring fissures between a material and another, as in the case of a refractory cement and, consequently, the problems which cause undesired solldifications which would entail the inconvenience that have been disclosed hereinbefore - 9 - WE CLAIM. 1. Refractory plate(s) for the lateral containment of molten metal in an apparatus for the continuous casting of thin, flat metallic products, said refractory plate(s) comprising one or more insert(s) of ceramic material, such as herein described, having substantially triangular shape, wherein, externally to said insert(s) a first casting of a silica alumina refractory material, such as herein described, containing ceramic fibres is provided; internally to said insert(s) and being bound peripherally by said insert(s), a second casting of a silica-alumina refractory material having a high content of zirconia, such as herein described, is provided; on the back of said insert(s) and said first casting and said second casting, there is provided a third casting of a SiC-based thixotropic material for supporting the said insert(s), said first casting and said second castinq and plurality of joints of ceramic fibres material, such as herein described, are provided at the contacting surface (s) between said insert(s) and at least one of said first, second and third castings, for thermal expansion; the arrangement being such that said second casting is disposed on said third casting such that said second casting is located at the central portion of the plate(s) defined by said insert(s). - 10 - Refractory plate (s) as claimed in claim 1, wherein said third casting of a SiC-based thixotropic material comprises a mixture the following components, expressed in weight percentage: - Al2O3 5 to 15% - sio2 2 to 4, 5% - SiC 80 to 95%; the remaining to 100 being substantially, impurities. 3. Refractory plate (s) as claimed in claims 1 or 2, wherein said second casting of a silica-alumina material having a high contents of Zr02 comprises a mixture of the following compounds, expressed in weight percentage: - ZrO2 40 to 60% - Al2O3 25 to 40% - SiO2 15 to 40%; the remaining to 100 being substantially impurities. 4. Refractory plate(s) as claimed in any of the preceding claims, wherein said first silica-alumina casting based on ceramic fibres comprises a mix of the following compounds, expressed as a percentage in weight: Al2O3 40 to 50% SiO2 30 to 40% Fe2O2 2, 5 to 4, 5%; the remaining to 100 being substantially impurities. - 11- 5 Refractory plate(s) as claimed in any of the preceding claims, wherein each insert of said plurality of ceramic inserts, comprises a mixture of the following compounds, expressed in percentage in weight with respect to the total weight of the mixture: -BN 20 to 55%; and at least one among the following compounds: -ZrO2 40 to 60% -SiC 2,5 to 7, 5%; -SiAlON (Silicon and aluminium oxinitride) 55 to 9 0% the remaining to 100 being substantially impurities. 6. Refractory plate(s)as claimed in any of the preceding claims, wherein said plurality of joints in ceramic fibres for the thermal expansion comprises a mixture of the following compounds, expressed in percentage in weight: -Al2O2 80 to 95% -SiC 2 to 25% the remaining to 100 being substantially impurities. 7. A process for producing the refractory plate(s) as claimed in claim 1, comprising the steps of : - positioning and optimised coupling, by means of gluing, of at least one insert of ceramic material on the bottom of a mould; - positioning with an optimised coupling of a plurality of joints constituted in ceramic fibres, on the peripheral walls of said at least one insert of ceramic material; - - 12 - - carrying out of a first casting of a refractory material, substantially constituted of a mixture of silica-alumina and ceramic fibres, at the external part of said at least one ceramic insert; - carrying out of a second casting of a silica-alumina refractory material having a high contents of ZrO2, at the central part of the plate and internally bounded by said at least one ceramic insert; - carrying out of a third casting of a refractory thixotropic material with a high contents of SiC, above said at least one ceramic insert, with respect to said first casting of refractory material and said second casting of refractory material having a high contents of ZrO2; removing the plate thus constituted from said mould, after a time of at least 24 hours; - thermal treating the plate at 110°C for a period of time of at least 24 hours; and - firing at low temperature said plate at least at 400°C for a time period of at least 1 hour 8. An apparatus for the continuous casting of flat, thin bodies, comprising : - at least a pair of counter-rotating rolls (1,2) having their longitudinal axes arranged parallel at a distance greater than the sum of their radiuses, and - 13 - - at least a pair of refractory plate(s)(5),/as claimed in any of claims 1 to 6 . 9. Refractory plate(s) for the lateral containment of molten metal in an apparatus for the continuous casting of thin, flat metallic products. 10. A process for producing the refractory plate(s), substantially as herein described, particularly with reference to and as illustrated in the accompanying drawings. Dated this 30th day of July, 1997. The present invention discloses refractory plate(s) for the lateral containment of molten metal in an apparatus for the continuous casting of thin, flat metallic products, said refractory plate(s) comprising: one or more insert(s) of ceramic material, such as herein described, having substantially triangular shape, wherein, externally to said insert (s) a first casting of a silica - alumina refractory material, such as herein described, containing ceramic fibres is provided; internally to said insert(s) and being bound peripherally by said insert(s), a second casting of a silica-alumina refractory material having a high content of zirconia, such as herein described, is provided, on the back of said insert (s) and said first casting and said second casting, there is provided a third casting of a SiC-based thixotropic material for supporting the said insert(s), said first casting and said second casting; and plurality of joints of ceramic fibres material, such as herein described, are provided at the contacting surface (s) between said insert (s) and at least one of said first, second and third castings, for thermal expansion; the arrangement being such that said second casting is disposed on said third casting such that said second casting is located at the central portion of the plate(s) defined by said insert(s).

Documents:

01418-cal-1997-abstract.pdf

01418-cal-1997-claims.pdf

01418-cal-1997-correspondence.pdf

01418-cal-1997-description(complete).pdf

01418-cal-1997-drawings.pdf

01418-cal-1997-form-1.pdf

01418-cal-1997-form-2.pdf

01418-cal-1997-form-3.pdf

01418-cal-1997-form-5.pdf

01418-cal-1997-pa.pdf

01418-cal-1997-priority document other.pdf

01418-cal-1997-priority document.pdf

1418-cal-1997-granted-abstract.pdf

1418-cal-1997-granted-claims.pdf

1418-cal-1997-granted-correspondence.pdf

1418-cal-1997-granted-description (complete).pdf

1418-cal-1997-granted-drawings.pdf

1418-cal-1997-granted-examination report.pdf

1418-cal-1997-granted-form 1.pdf

1418-cal-1997-granted-form 2.pdf

1418-cal-1997-granted-form 3.pdf

1418-cal-1997-granted-form 5.pdf

1418-cal-1997-granted-letter patent.pdf

1418-cal-1997-granted-pa.pdf

1418-cal-1997-granted-reply to examination report.pdf

1418-cal-1997-granted-specification.pdf

1418-cal-1997-granted-translated copy of priority document.pdf