Patent Publication Number: US-2021178460-A1

Title: Crystallizer for continuous casting and method for its production

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 14/901,642, filed Dec. 28, 2015, which is a § 371 national stage entry of International Application No. PCT/IB2014/062721, filed Jun. 30, 2014, which claims priority to Italian Patent Application No. UD2013A000090, filed Jun. 28, 2013, all of which are incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns a crystallizer for continuous casting, usable in the iron and steel making industry to cast billets, blooms or other similar products, of any type and cross section. The invention also concerns the method for its production. 
     BACKGROUND OF THE INVENTION 
     Different crystallizers for continuous casting are known, suitable to cast billets, blooms or other iron and steel products, each having a tubular body provided with a through longitudinal cavity with a desired cross section, corresponding to the cross section of the product to be cast, for example circular, elliptical or polygonal (e.g. octagonal), and in which the liquid casting metal is suitable to pass. On the wall or walls which define the tubular body of the crystallizer and which have a thickness of some tens of millimeters, a plurality of channels are normally made longitudinally, which are part of a closed cooling circuit in which a cooling liquid, for example water, is made to circulate. 
     Some examples of crystallizers for continuous casting and corresponding production methods are described in the Italian applications for patents of industrial invention UD2102A000192 and UD2013A000013 filed by the present Applicant, which are incorporated here as reference. 
     Another example of a crystallizer for continuous casting is described in the document EP-A-1.468.760 and comprises a first tubular body, or internal tubular body, which defines a casting channel for the liquid metal, and a second tubular body, or external tubular body, which is associated externally to the first tubular body. 
     In particular, the internal tubular body is provided, on its external contact surface with the external tubular body, with support ribs and connection ribs alternating with the support ribs. 
     The support ribs and the connection ribs protrude toward the outside and extend along the axial extension of the crystallizer. 
     The function of the support ribs is to maintain the external tubular body distanced from the internal one, while the connection ribs are inserted in attachment seatings made on the internal surface of the external tubular body, defining a fixed-joint mechanical coupling, making the internal tubular body able to be disassembled from the external tubular body. 
     Moreover, the connection ribs and the support ribs define, between the internal tubular body and the external tubular body, a plurality of hollow spaces in which a cooling fluid flows. 
     The fixed-joint mechanical coupling between the internal tubular body and the external tubular body does not guarantee a hydraulic seal of the cooling fluid in the hollow spaces, since the support ribs have only a distancing function for the external tubular body and are not able to guarantee the hydraulic seal between adjacent hollow spaces. 
     This disadvantage is linked to the rigidity, and the geometric and dimensional tolerances of each of the two tubular bodies and to the fact that the latter are not intimately coupled to each other. 
     In particular, document EP-A-1.468.760 provides that the internal tubular body is made of metal material, for example copper, while the external tubular body is made of a metal or non-metal material, a composite for example, such as laminate carbon. 
     Moreover, it is known that traditional crystallizers are affected by a series of disadvantages due to the variation in the internal conicity of the crystallizer, at least around the meniscus zone. Indeed, mainly in this zone, there is a tendency to expand toward the outside, due to the heat stresses deriving from the contact temperature between the liquid steel and the wall of the crystallizer. This causes a reduction in conicity between meniscus and upper entrance section, and a greater conicity than the specification conicity in the lower segment of the crystallizer, always with respect to the meniscus zone. This causes a deterioration in the quality of the cast product because of the alteration in the functioning conditions and consequent poor heat conduction between the skin of the steel and the cooled wall of the crystallizer itself. 
     Consequently, the probability of leakages of liquid steel from the skin, also called “breakout”, is increased, following the lack of heat conduction which causes the skin to stick to the walls of the crystallizer, called “sticking”. 
     One purpose of the present invention is to make a crystallizer for continuous casting, with cooling channels incorporated in the walls, which overall has an increased structural rigidity without increasing the thickness of its walls, in order to guarantee an increased casting efficiency and an increased quality of the product exiting from the crystallizer. 
     Another purpose of the present invention is to make a crystallizer for continuous casting, of the type indicated above, that is simple in construction and at the same time has a reduced cost compared to known crystallizers, even when the crystallizer has large sizes, for example a diameter or width equal to or more than 800 mm, reducing to a minimum the use of metal, for example copper, needed to make the walls of its tubular body. 
     It is also a purpose of the present invention to make a crystallizer for continuous casting that allows to obtain cast metal products of high quality, keeping the specification conicity substantially unvaried, when both hot and cold. 
     Another purpose of the present invention is to make a crystallizer for continuous casting, of the type indicated above, that can be easily used, without any contraindication, in association with a mechanical agitator, also called stirrer. 
     Another purpose of the present invention is to make a crystallizer for continuous casting, of the type indicated above, that is reliable and can be used, without any contraindication and with maximum efficiency, even with a radioactive rod used to detect the level of liquid metal inside the crystallizer during casting. 
     Another purpose of the present invention is to perfect a method to make a crystallizer for continuous casting, of the type indicated above, that allows to reduce production costs without reducing the characteristics of structural rigidity, safety, reliability and thermal and thermo-mechanical efficiency of the crystallizer itself. 
     Another purpose of the present invention is to perfect a method that allows to make a crystallizer for continuous casting, of the type indicated above, easily and with simple work steps, that can have any shape and cross section, for example circular, elliptical or polygonal, e.g. octagonal. 
     The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages. 
     SUMMARY OF THE INVENTION 
     The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea. 
     In accordance with the above purposes, a crystallizer for continuous casting, according to the present invention, comprises a tubular body with at least a wall that defines a through longitudinal casting cavity and a plurality of longitudinal grooves made at least on a part of an external surface of the at least one wall and open toward the outside thereof. 
     According to one characteristic of the present invention, a covering binding, comprising one or more overlapping layers of fiber material, is irremovably wound around the external surface of the at least one wall, so as to create an indivisible whole between the at least one wall with the longitudinal grooves and the covering binding. 
     Here and hereafter in the description and in the claims, by covering binding we mean a material comprising a plurality of fibers adjacent to each other to define one or more bands that, once in position, cover at least part of the external surface of the wall. 
     The layers of fiber can be impregnated with a polymer material, which, once the covering binding has been wound around the external surface of the wall, is polymerized and determines the solid and irremovable attachment of the covering binding to the wall. 
     This allows to obtain a crystallizer for continuous casting that maintains its specification conicity unchanged whether it is hot or cold, thanks to the reinforcement structure that the external covering binding achieves for the walls of the crystallizer. 
     Indeed the covering binding, wound tightly around the crystallizer in a direction mainly transverse to its longitudinal direction, limits the deformations and movements of the walls, maintaining the internal conicity, while allowing the longitudinal dilation due to heat phenomena for example between 0 and 4 mm. 
     According to a first form of embodiment of the present invention, the covering binding is in direct contact with the external surface of the at least one wall and closes the longitudinal grooves. Corresponding cooling channels are thus obtained, configured to make a cooling liquid flow inside them, for example water, suitable to cool the tubular body of the crystallizer. 
     According to a second form of embodiment of the present invention, as an alternative to the first, the covering binding is in direct contact with a metal layer made with electrolytic deposition techniques; the metal layer, in its turn, is in contact with the external surface of the at least one wall and closes the longitudinal grooves to form a corresponding plurality of cooling channels. 
     Therefore, unlike the technical solution described in EP-A-1.468.760, which provides to use electrolytic deposition as a solution to oxidation phenomena, the present invention describes the use of electrolytic deposition with the purpose of creating sealed cooling channels on the external surface of the walls of the crystallizer. 
     In this way, the covering binding makes rigid the whole made by the at least one wall of the crystallizer and the metal layer associated thereto. 
     According to a third form of embodiment of the present invention, alternative to the first two, it is provided that the longitudinal grooves are closed by at least a plate associated to the external surface of the at least one wall so as to define a corresponding plurality of cooling channels inside which a cooling liquid flows. 
     In this case, the covering binding is in direct contact with the at least one plate so as to reinforce and increase the security of the connection between the at least one plate and the at least one wall. 
     According to a fourth form of embodiment of the invention, it is provided that the longitudinal grooves are closed by at least a lamina made of a fiber-reinforced polymer material, fiberglass for example, associated to the external surface of the at least one wall to define a corresponding plurality of cooling channels inside which a cooling liquid flows. The covering binding, in this case, is located in direct contact with the lamina of fiber-reinforced polymer material in order to make rigid the whole made by the at least one wall and the lamina of fiber-reinforced polymer material. 
     The covering binding can be wound around the wall defining even variable thicknesses in a longitudinal direction in the most stressed zones, for example the meniscus zone. 
     The covering binding, in order to increase resistance and rigidity, has a variable thickness along the longitudinal extension of said tubular body to define at least an upper portion, substantially comprising the meniscus area during the casting, defining a thickened zone having a thickness comprised between 1.1-1.25 times the thickness of a non-thickened zone in a lower portion of the tubular body. 
     The variation in thickness in a longitudinal direction of the covering binding can even be some millimeters. Merely by way of example the covering binding, in the non-thickened zone, has a thickness comprised between 1 mm and 8 mm, and, in the thickened zone, has a thickness comprised between 1.1 mm to 10 mm. 
     The variable thickness of the fibers which surround the crystallizer, after complete polymerization of the covering binding, allows to work with machine tools on the external containing surface so as to obtain seatings for housing packings or break-pins. 
     The method to make a crystallizer for continuous casting, according to the present invention, comprises a step in which a tubular body is made, of metal for example, more specifically of copper, with at least a wall that defines a through longitudinal casting cavity and a plurality of longitudinal grooves made at least on one part of the external surface of the at least one wall and open toward the outside thereof. 
     According to another characteristic of the present invention, the method according to the present invention also comprises a step in which a covering binding, comprising one or more layers of fiber material, is associated to the external surface of the at least one wall. 
     In particular, the covering binding comprises a band made using at least a fiber, impregnated or pre-impregnated with for example a volumetric ratio of fibers of 60%, such as carbon, and glue or polymer resin of 40%. The polymer material is the type resistant to high temperatures, that is, equal to or more than 100° C., such as a polymer for example chosen from the group comprising polyamide, epoxy or polyester resins. 
     The fibers can be chosen from a group comprising carbon fibers, glass fibers, aramid fibers or similar. 
     The covering binding in fiber, which becomes rigid when the polymer solidifies by polymerizing, can be applied using any known technique, including the filament winding technique. 
     The polymerization of the polymer can occur through heat polymerization steps, that is, reticulation of the resin, called curing. 
     During the curing, or solidification, step, the crystallizer is heated to a temperature comprised between 30° C. and 120° C., preferably between 70° C. and 100° C., and kept at this temperature for a period comprised between 20 and 400 minutes, preferably between 120 minutes and 360 minutes, more preferably around 240 minutes. These conditions determine the reticulation of the polymer resin and therefore a solidarization of the binding to the wall or walls. 
     This allows to guarantee better characteristics of resistance and heat consolidation depending on the type of resin applied. 
     In possible forms of embodiment, after the curing step, a post-curing, or hardening, step can be provided during which the crystallizer is heated to a temperature comprised between 80° C. and 200° C., preferably between 100° C. and 150° C., and kept at this temperature for a period comprised between 1 hour and 20 hours, preferably at least about 120 minutes, more preferably around 480 minutes. 
     In possible forms of embodiment, for the whole duration of the curing and/or post-curing steps, the crystallizer is kept in rotation around its own axis. 
     According to one possible implementation, the crystallizer, after the curing and possibly post-curing steps, can be subjected to a forced cooling. 
     The operation of winding the covering binding on the wall can include the installation, on a suitable apparatus and by means of a dedicated apparatus, of the wall in rotating mode around an axis of rotation and subsequent winding of the covering binding perpendicularly to the axis of longitudinal development, or with a winding angle comprised between 0° and 10°, preferably between 0° and 5°, with respect to the perpendicular to the axis of longitudinal development of the crystallizer. 
     The winding operation can occur with a controlled tension of the fibers, for example from 1N and 50N per fiber. 
     The solution of using the covering binding, in particular of fiber, around the tubular body of the crystallizer, which is new and original, allows to obtain at least the following advantages: 
     increasing the rigidity of the hollow tubular body of the crystallizer;
 
maintaining the internal conicity of the crystallizer both when hot and when cold;
 
maximizing the efficiency of a possible radioactive rod associated to the crystallizer, given that the covering binding is transparent to radiations;
 
containing the costs of production of crystallizers of any shape, or with any cross section, for example polygonal, circular, or elliptical, and even of considerable sizes, for example with diameters, or widths, equal to or more than 800 mm;
 
reducing to a minimum the thickness of the walls which define the tubular body of the crystallizer and therefore minimum use of metal, for example copper, of which they are made;
 
prolonging the life of the crystallizer;
 
improving the quality of the cast product;
 
possibility of working with machine tools on the solidified covering binding, for example to define grooves for sealing rings or holes for the insertion of break-pins.
 
     According to possible solutions of the method according to the present invention, before winding the one or more layers of fiber material it provides to fill the longitudinal grooves with disposable material, for example wax, to deposit a metal layer on the external surface of the at least one wall by electrolytic deposition techniques, in order to close the longitudinal grooves, and to subsequently remove the disposable material from the longitudinal grooves so as to define corresponding cooling channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other characteristics of the present invention will become apparent from the following description of some forms of embodiment, given as a non-restrictive example with reference to the attached drawings wherein: 
         FIG. 1  is a perspective and schematized view of a crystallizer for continuous casting according to a first form of embodiment of the present invention; 
         FIG. 2  is an enlarged detail of the crystallizer in  FIG. 1 ; 
         FIG. 3  is a perspective and schematized view of a detail of a crystallizer according to a second form of embodiment of the present invention; 
         FIG. 4  is a schematized view of a detail of a crystallizer according to a third form of embodiment of the present invention; 
         FIGS. 5 and 6  are schematized views of possible variants of the crystallizer according to the present invention. 
     
    
    
     To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications. 
     DETAILED DESCRIPTION OF SOME FORMS OF EMBODIMENT OF THE PRESENT INVENTION 
     With reference to  FIGS. 1 and 2 , a crystallizer  10  for continuous casting according to the present invention, in a first form of embodiment, comprises a tubular body  11  with a wall  12 , for example made of copper or its alloys, which defines a through longitudinal casting cavity  13 . The thickness of the wall  12  is for example comprised between 10 mm and 50 mm. 
     There is a plurality of longitudinal grooves  14  on at least an external part of the wall  12 . Each longitudinal groove  14  is open toward the outside of the wall  12 . 
     A covering binding  15 , which in this case comprises one or more layers of a band  16  of fiber, impregnated or pre-impregnated with a polymer resistant to high temperatures (that is, equal to or higher than 100° C.), is in direct contact with the external surface of the wall  12  and closes the longitudinal grooves  14  from the outside. In this way corresponding channels  17  are made, configured to make a cooling liquid, for example water, flow inside them. In this specific case, it is provided that the band  16  defines a plurality of layers wound on the external surface of the wall  12  of the crystallizer  10 . 
     In a second form of embodiment, a crystallizer  110  ( FIG. 3 ) according to the present invention comprises, interposed between the covering binding  15  and the wall  12 , a metal layer  18  made with electrolytic deposition techniques, for example as described in the application for a patent of industrial invention UD2013A000013 cited above. 
     In this case, it is the metal layer  18  that hermetically closes the longitudinal grooves  14  from the outside of the wall  12  and defines the plurality of cooling channels  17 . 
     Therefore, in this second form of embodiment, the covering binding  15  is in direct contact with the metal layer  18 , in order to make rigid the whole made up of the latter and the wall  12 . This allows to have a very contained thickness of the metal layer  18 , for example in the range of one or two millimeters. The covering binding  15  in this case has a containing function of the metal layer  18  and guarantees the seal of the latter even at high working pressures of the cooling fluid circulating in the channels  17 . 
     According to the form of embodiment in  FIG. 6 , the metal layer  18  can be replaced by a lamina  23  made of a fiber-reinforced polymer material which, closing the longitudinal grooves  14  from the outside, defines the corresponding plurality of cooling channels  17 . The covering binding  15  is wound intimately in direct contact with the lamina  23  to make rigid the whole constituted by the wall  12  and the lamina  23 . 
     According to a third form of embodiment, a crystallizer  210  ( FIG. 4 ) according to the present invention comprises a tubular body  211  provided with a plurality of walls  212  defining a longitudinal casting cavity  213 . The longitudinal grooves  14 , open toward the outside, are made on the external surface of the walls  212 , by removing material. At least one plate  219 , in this specific case four plates  219 , are associated to the external surface of the tubular body  211 , for example welded or glued, and are provided to close the longitudinal grooves  14  made on the walls  212  of the tubular body  211  from the outside and to define the cooling channels  17 . 
     The plates  219  can be associated to the external surface of the tubular body  211 , for example, by braze welding or structural gluing, in the same way as described in the Italian application for a patent of industrial invention UD2012A000193 in the name of the Applicant. 
     In this case too, as in the first form of embodiment, the covering binding  15  is in direct contact with the surface of the plates  219  that is external during use, to reinforce them and increase the secure seal of the braze welding. 
     Forms of embodiment of the present invention provide that the covering binding  15  has a constant thickness along the longitudinal extension of the tubular body  11 ,  211 . 
     Other forms of embodiment, one of which is shown in  FIG. 5 , provide that the covering binding  15  is provided with a thicker portion  20  that has a greater thickness than the thickness along the longitudinal extension of the tubular body  11  or  211 . In this way it is possible to generate zones of the crystallizer  10  with variable resistance and rigidity along its longitudinal extension that are determined, for example, depending on a variable development of the pressure of the cooling fluid in the cooling channels  17  or on different conditions of mechanical and/or heat stress to which it can be subjected during normal use. 
     In particular, the thickness of the covering binding  15 , when completely wound, is greater in an upper-zone, substantially comprising the meniscus area during the casting, than along the entire length of the crystallizer  10 , that is a lower non-thickened zone. 
     The covering binding  15  in the thickened zone has a thickness comprised between 1.1-1.25 times the thickness of the non-thickened zone. Merely by way of example, the covering binding  15  in the thickened zone has a thickness comprised between 1.1 mm and 10 mm. 
     According to other forms of embodiment of the present invention, shown for example in  FIG. 6 , mechanical workings, for example to define circumferential seatings  21  for housing sealing rings or holes  22  for the insertion of break-pins, can be made on the covering binding  15 . 
     In particular, at the end of the operation of winding the covering binding  15 , and before the complete polymerization of the polymer, a hole  22  is made through the layer of fiber material partially affecting the thickness of the crystallizer  10 . 
     A retaining element, for example a retaining key,  24  is inserted into the hole  22  to bind the fibers to the crystallizer  10 . 
     The hole  22  is then covered with a patch  25  made of impregnated fibers, for example carbon fibers, so that the retaining element  24  cannot come out and the fiber structure is cured as described above. 
     This retaining element  24  is intended to prevent any sliding of the fibers once cured to the crystallizer  10 . 
     The method for producing each of the crystallizers  10 ,  110 ,  210  for continuous casting described heretofore comprises a step in which the tubular body  11 ,  211  is made, with the wall  12  or walls  212  that define the longitudinal cavity  13 ,  213  and the plurality of longitudinal grooves  14 , made for example by removing material, such as milling, at least on one part of the wall  12  or walls  212 , and open toward the outside thereof. 
     The method also comprises a step in which a covering binding  15 , as described heretofore, is associated to the external surface of the wall  12  or walls  212 . 
     In particular, the binding  15  comprises the band  16  made with one or more overlapping layers, using at least a fiber impregnated or pre-impregnated with a polymer resistant to high temperatures, as indicated above, that is chosen for example from a group comprising polyamide, epoxy or polyester resins. 
     It can be provided, for example, that the wall  12  or walls  212  is or are installed on a winding machine, for example by means of clamps or specific equipment to allow the subsequent winding operation of the fibers around it. 
     The fibers can be polymerized in different curing passes, for example a curing, or solidification, step at a temperature between 30° C.-120° C., preferably between 70° C. and 100° C., for a period comprised between 20-400 minutes, preferably between 2 hours and 360 minutes, more preferably around 240 minutes, followed by a post-curing, or hardening, at a temperature between 80° C.-200° C., preferably between 100° C. and 150° C., for a period comprised between 60-1200 minutes, preferably at least about 360 minutes, more preferably around 480 minutes, depending on the resin applied. 
     For example, the covering binding  15  can be applied using the filament winding technique. 
     It is clear that modifications and/or additions of parts may be made to each of the crystallizers  10 ,  110 ,  210  for continuous casting as described heretofore, without departing from the field and scope of the present invention. 
     It is also clear that, although the present invention has been described with reference to some specific examples of embodiments, a person of skill in the art shall certainly be able to achieve many other equivalent forms of crystallizer for continuous casting and/or other methods to make them, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.