Patent Publication Number: US-2018036794-A1

Title: Mold for continuous casting

Description:
FIELD OF THE INVENTION 
     The present invention concerns a mold for continuous casting configured to cast metal products of different section and sizes, such as, merely by way of example, slabs, blooms or billets of any type and section, round or polygonal with at least three sides, such as square, rectangular, double T-shaped of the type called beam blanks, U-shaped, sheet piles or similar or comparable sections. Here and hereafter in the description the term “slab” shall include conventional slabs, thick, thin or ultra-thin. 
     Furthermore, the present invention concerns molds for the continuous casting of steels or its alloys, but with the natural adaptations, the teachings of the invention can also be applied for the continuous casting of alloys of copper, brass, aluminium or other metals. 
     The present invention also concerns a continuous casting method. 
     BACKGROUND OF THE INVENTION 
     In the field of continuous casting it is known that it is necessary to reach high casting speeds in order to increase the overall production capacity of a steel plant. 
     It is also known that reaching high casting speeds is correlated to the optimization of a plurality of technical and technological parameters thanks to which the liquid metal is partly solidified. 
     These parameters affect the capacities of the crystallizer function to support the high heat and mechanical stresses and wear to which it is subjected during use. 
     We use the expression “crystallizer function” in that a mold has the crystallizer function associated with its internal surface, which cooperates with the liquid metal that has to be solidified. Hereafter we use the word crystallizer both to indicate the internal wall of the monobloc mold, and also to indicate the removable body inside which the liquid metal is cast to be solidified. 
     Solutions are also known, of molds having at least the internal surface, with the crystallizer function, having a conical shape with the taper for example comprised between 0.8%/m and 5%/m, opening toward the edge where the metal material is introduced. 
     It is also known that in a mold, during casting, the heat flux along the longitudinal extension has a peak around the zone of the meniscus, i.e. in correspondence with the zone where, during casting, the level of the liquid metal is positioned. 
     It is also known that during the design and production of a crystallizer, in the tubular body that defines the crystallizer, a zone is defined in which, during use, the meniscus M of the liquid metal will be positioned. 
     The high heat flux present in the zone of the meniscus M generates an unwanted deformation of the mold, which causes different problems depending on the type of the mold. 
     Hereafter we shall consider separately the problems that arise for tubular molds and for plate-type molds, for example used for casting slabs. 
     The problems that arise in the case of tubular molds, i.e. configured to cast blooms or billets, which the present invention intends to overcome, are described hereafter with reference to  FIGS. 1, 2   a ,  2   b  and  2   c.    
     The deformation profile of the wall can be different, depending on how the mold is made, and the deformation can also vary inside an integral mold and a mold with a replaceable wall with crystallizer function. 
     The deformation profile can be almost uniform over the whole periphery of the crystallizer function, or different on one or more specific parts of the periphery, mainly depending on the general geometry of the mold. In fact, the deformation can be different along the periphery of the crystallizer depending on the different behaviors that the point-to-point shape of the geometry allows. 
     Furthermore, the deformation profile can assume different values both depending on the geometric configuration of the section of the wall, and also depending on other factors, such as heat exchange, temperature of the molten metal, etc. 
     In particular,  FIG. 1  concerns a mold  10  suitable to cast round products and is shown in a condition excessively and deliberately deformed, to give a clearer understanding of the negative phenomena that occur and that prevent an increase in the casting speed in known solutions. 
     The liquid metal  12  is discharged continuously into the mold  10  until a determinate level or meniscus M is reached and, above it, lubricating materials  16  are distributed, such as lubricating powders or oils which, on contact with the liquid metal  12 , become liquid and define a layer of lubricating liquid  17  that is interposed between the liquid metal  12  and the lubricating materials  16 . 
     The solidification of the liquid metal  12  begins, in a known manner, in correspondence with the meniscus M and the internal surface  11 , with the formation of a solid layer or skin  14 , which progressively increases in thickness. 
     Due to the high heat flux around the meniscus M, the internal surface  11  of the mold  10  deforms to define a concave portion  15  practically under the level of the meniscus M, and a portion with negative taper  13  near and above the meniscus M. 
     Merely by way of example, the concave portion  15  can be subject to a deformation that can even reach around 0.25 mm and more, compared with its non-deformed condition. 
     By negative taper we mean that the internal surface  11  has an inclination, indicated in  FIG. 1  by −α, that faces toward the inside of the casting cavity of the mold  10 . 
     Negative taper also occurs, during use, in the case where the internal surface  11 , when the mold is cold, is made with positive taper as described above. 
     During casting, the mold  10  is made to oscillate, with a defined and desired motion, also in terms of values, in a direction (indicated in the drawings by the arrow F) substantially parallel to its longitudinal extension, both to prevent the cast liquid metal  12  from welding with the internal surface  11 , and also to facilitate the descent of the cast product with its layer of skin  14  in formation. 
     During the upward movement of the mold  10  the internal surface  11  of the mold  10  is wet by the lubricating liquid  17  over all its perimeter. 
     During the downward movement of the mold  10 , also called “negative strip”, the mold  10  transports the lubricating liquid  17  downward but, due to the presence of the portion with negative taper  13 , the mold  10  impacts on the solidified first skin  14 , thinning the lubricating liquid  17  and interrupting it if the inclination −α is high. This effect, which occurs in the state of the art, heretofore has not allowed to exceed casting speeds higher than 2.5 m/min for casting round billets and 7 m/min for casting square billets. 
     The impact of the mold  10  against the skin  14  also causes deformations or oscillation marks, in which traces of the lubricating liquid  17  can be deposited. 
     A lack of or insufficient lubrication causes possible welding, temporary and localized, of the skin  14  on the internal surface  11 , and also axial tensions and transverse cracks of the skin  14 , with consequent breakages, also called “bleeding”. 
     During the downward movement of the mold  10 , the portion with negative taper  13  ensures a sure contact of the skin  14  with the internal surface  11  and therefore an optimal heat exchange. 
     This region of the mold  10  with sure contact can extend for a distance P from the meniscus M which, in the case of continuous casting of round sections, can vary, merely by way of example, between 10 mm and 20 mm depending on the casting speed. 
     In the region located under the portion with negative taper  13 , in correspondence with the concave portion  15 , between the internal surface  11  and the skin  14 , also because of the shrinkage of the cast product, a large interspace or gap  18  is generated, consisting of air and solid lubricant  19  that is deposited on the internal surface  11  of the mold  10 . 
     The layer of air and solid lubricant generates a high heat barrier that prevents the mold  10  from removing heat from the skin  14  which is forming; this can lead to localized fusions of the forming skin  14  with a consequent reduction in its thickness. 
     With reference to  FIGS. 2 a , 2 b  and 2 c   , the negative phenomena are described that occur and impede an increase in the casting speed in known molds  10  for casting square products. 
     It is quite clear that similar problems also occur in molds  10  configured to cast products with a polygonal section. 
       FIG. 2 a    shows the development of the internal surface  11  of the mold  10  in correspondence with the meniscus M, with a line of dots and dashes in its non-operating or cold condition, and a line of dashes in its operating or hot condition. 
     As can be seen, the internal surface  11  in proximity to the flat walls is subjected to a radial dilation whereas in correspondence with the rounded connection portions, and for a region of the flat walls comprised between 10 mm and 15 mm from the rounded connection regions, is subjected to a more accentuated deformation toward the outside. 
       FIGS. 2 b  and 2 c    are views in a longitudinal section along the section line B-B and respectively C-C of the mold  10  in  FIG. 2 a    respectively in a zone in correspondence with one of the flat walls and in correspondence with one of the rounded connection portions. 
     In  FIG. 2 b    we can see how the internal surface  11 , in its flat region, has a positive taper, i.e., open toward the entrance end of the liquid metal  12  for the whole longitudinal development. 
     This condition ensures a sure contact between the skin  14  that is generated and the internal surface  11 , guaranteeing an optimal heat exchange and a homogeneous supply of lubricating liquid  17  between the skin  14  and the internal surface  11  of the mold  10 . 
     On the contrary, in  FIG. 2 c   , which shows the behavior in correspondence with the connection portion, we can see how the deformation development of the internal surface  11 , in proximity to the connection zones, is comparable to the one shown in  FIG. 1 , and has the portion with negative taper  13  and the concave portion  15  as described above. In the connection zones the same problems occur as those described previously with reference to  FIG. 1 . 
     In the portion with negative taper  13 , the skin  14  is in contact with the internal surface  11  for a height of about 20 mm-50 mm from the meniscus M, whereas in correspondence with the concave portion  15  the skin  14  detaches from the internal surface  11  after about 20 mm, with a consequent deterioration in its capacity to remove heat and difficulties in the solidification of the liquid metal. This can cause localized welding of the skin  14  to the internal surface  11  in the zone comprised between the flat wall and the rounded connection portion of the internal surface  11  of the mold  10 . 
     For connection radii of the edges of the cast section with sizes smaller than 12 mm, for example for radii of curvature of 3-6 mm, there is a further disadvantage, i.e. cracks on the edges, also called “off-corner cracks”. 
     In particular, as shown in  FIG. 2 a   , during solidification, the portion of skin  14  in proximity to the flat walls has a much bigger thickness than that near the rounded connection portions. 
     The portion of skin  14  located in correspondence with the flat walls exerts traction on the skin  14  located in the edge regions, entailing a thinning thereof and a further detachment from the internal surface  11  of the mold  10 . 
     In proximity to the edge, the skin  14  is therefore subjected to localized microfusions and to a deterioration in the heat fluxes which the internal surface  11  is no longer able to remove due to the detachment of the skin  14 . 
     Following this, in the zones of the edges there is drastic reduction of skin  14  growth, and a thinning of the latter and cracks in the cast product are generated, with a consequent deterioration in quality. 
     Another disadvantage that limits the increase in casting speed is connected to the stresses to which the zone of the edges is subjected where the material is deformed plastically, causing a rhomboidal shape of the mold  10  and consequently also of the cast product. The rhomboid shape of the mold is also due to the detaching from the mold of the skin of the solidifying product in its edge zone. 
     Plate-type molds, usually used for casting slabs, generally comprise two or more walls, or plates, which define between them the casting channel for the molten metal. 
     Cooling devices are associated with each of the walls, suitable to cool the wall by making cooling liquid hit the surfaces of the walls. 
     In particular, a first solution is known in which the cooling devices are at least partly integrated in the thickness of the wall, to define walls of the integral type. 
     Integral-type walls generally comprise a plurality of cooling channels made in the thickness parallel to the casting direction of the metal to be cast and uniformly distributed along the section development of the wall. 
     A cooling liquid, generally water, is made to pass in the cooling channels, equicurrent or counter-current, with respect to the casting direction of the metal. However, this solution is particularly costly due to the large quantity of material required to make the mold, and the complex mechanical operations required, and precisely for this purpose it is necessary to identify technical solutions that allow to increase the working life of such molds. 
     Alternatively, a second solution is also known, in which the walls are made replaceable and the cooling devices act externally, or at least partly externally, to the wall and are re-used even if the wall is replaced. 
     Walls or plates of the replaceable type are provided, on the surface that is external during use with respect to the casting cavity, with a plurality of grooves with a development substantially parallel to the casting direction of the metal. 
     The grooves are closed, on the side facing toward the outside, by counter-plates or by a combination of closing elements, usually blades, partly inserted into the depth of the grooves and with external counter-plates that keep the blades in position. In this way the counter-plates or the blades define in the wall cooling channels for the passage of the cooling liquid. The cooling channels are open in proximity to the end edges of the wall so as to introduce and discharge the cooling liquid. 
     The counter-plates are connected to the walls by means of connection devices, usually threaded elements, also called tie-rods, such as screws or studs. The threaded elements are screwed into holes provided in the thickness of the wall and open toward the external surface thereof. 
     The presence of holes for threaded elements in the wall makes it impossible to make the grooves, in such zones, for the passage of the cooling liquid. This does not allow to obtain an equal distribution of the cooling channels in the cross section development of the wall, and therefore to obtain a uniform cooling. 
     The non-uniform cooling entails surface cracks in the wall and in the product cast, with a consequent reduction in the duration of the walls and a deterioration in the quality of the cast product. Furthermore, the high heat flux present at least in correspondence with the meniscus, combined with a non-uniform cooling of the wall, entails extremely high heat dilations, for example of about 0.3 mm, which cannot be supported by the threaded elements. 
     All the problems described above with reference to tubular molds and plate-type molds have considerably limited the casting speeds obtainable and drastically reduced the working life of a mold. 
     The state of the art has not found a satisfactory solution to all these problems. 
     For example, in an attempt to increase the casting speed, an unsatisfactory cooling is obtained, and hence an insufficient thickness of the skin at exit from the mold  10 , with consequent problems of breakage of the skin. 
     To increase the heat exchange efficiency, it is also known to increase the speed of transit of the cooling liquid in the mold. However, the increase in the speed of transit of the cooling liquid is not directly proportional to the increase in heat flux that the cooling liquid is able to remove. 
     In fact, once a limit transit speed of the cooling liquid has been reached, the removable heat flux is stabilized at an asymptotically stable value and can no longer be increased. This disadvantage is due, in particular, to the generation of a limit layer of steam that is generated near the interface surfaces on which the cooling liquid flows. 
     The limit layer of steam generates a heat barrier for the cooling liquid that flows above the limit layer of steam and therefore gives no possibility of removing further heat from the wall. 
     It is also known that in the interface surfaces on which the cooling liquid flows, the cooling liquid reaches temperatures of about 180° C. or more. To prevent the cooling liquid from boiling near the interface surfaces, it is also known to put the cooling liquid in the cooling channels or interspaces at high pressure, for example about 16 bar. Such high pressures in the mold generate mechanical stresses that reduce its working life, can cause surface cracks and can even cause the mold to explode, if the cooling liquid reaches the hot metal. 
     Molds are also known, from U.S. Pat. No. 5,190,593, U.S. Pat. No. 4,494,594, JP-A-H07.88598, EP-A-1.785.206, JP-A-H07.314096 and JP-A-S63.188452, comprising a tubular body and delivery nozzles that spray nebulized water, using spray techniques, onto the external surface of the tubular body in order to cool it. This solution provides to position the delivery nozzles in a chamber at room conditions and inside which the tubular body to be cooled is installed. The delivery nozzles deliver a spray of cooling liquid into the environment of the chamber and which reaches the tubular body in order to cool it. The nebulization chamber is connected with the outside so as to allow the water delivered to flow away. The spraying of the liquid means that the cooling liquid is reduced into extremely small particles that are directed toward the wall of the tubular body, for example orthogonally to the external surface of the tubular body. 
     The high heat flux present near the wall and the limited sizes of the particles lead to an instantaneous vaporization of the cooling liquid. 
     These known solutions do not allow to obtain high heat exchange coefficients, they do not allow to reach high productivity and they drastically reduce the working life of the mold. 
     The present invention therefore proposes to give an answer to the problems indicated above by way of example, supplying a solution that allows both to increase the casting speeds, to increase the working life of the walls and also to obtain continuously cast products with optimum surface quality. 
     The present invention also has the purpose, at least with regard to tubular crystallizers, to eliminate the formation of internal cracks in the edge zone, called “off-corner cracks”, to make solidification uniform over the whole perimeter of the tubular mold, eliminating the rhomboid shape of the cast product, and to minimize the depth of the oscillation marks. 
     The present invention also has the purpose, at least with regard to plate-type molds, to reduce mechanical stresses acting on the threaded elements, and to reduce the possibility of longitudinal cracks on the plates. 
     One purpose of the present invention is to obtain a mold for continuous casting, and the connected crystallizer, which allows to reach higher, even much higher casting speeds than current ones, and hence allows to increase the productivity of a steel plant. 
     Merely by way of example, the purpose of the present invention is to reach casting speeds of at least 20 m/min for tubular molds and even higher speeds for slabs. 
     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 mold for the continuous casting of a liquid metal comprises at least one wall that defines at least part of a casting cavity in which to cast the liquid metal, and cooling devices configured to cool the wall by a flow of cooling liquid on one or more interface surfaces of the wall. According to the present invention, the one or more interface surfaces are associated at least in part with an interspace, comprised between the wall and a containing body outside the wall, in the case of a replaceable type mold, or with one or more cooling channels made in the wall, for example in the case of an integral type mold. 
     Furthermore, the cooling devices comprise introduction members and discharge members configured to generate a controlled flow of the cooling liquid along the interspace, or along the cooling channels. 
     According to another aspect of the invention, the introduction members and the discharge members are configured to generate the flow of cooling liquid at a pressure higher than ambient pressure. 
     According to one aspect of the present invention, the cooling devices comprise a feed chamber associated with at least a delivery member configured to deliver, in the interspace or in the cooling channels, at least one jet of cooling liquid, in the flow of cooling liquid, and in a delivery direction incident with respect to the controlled flow and against one or more portions of the interface surface of the wall. The jet interacts with the flow of cooling liquid in order to generate therein a perturbation inside the interspace, or the cooling channels, and to increase the heat exchange capacity. 
     By incident direction we mean a direction not parallel or substantially parallel to the oblong development of the mold, i.e. the direction of normal flow of the cooling liquid, for example in the interspace or the cooling channels. 
     The cooling devices according to the present invention are particularly effective compared with solutions known in the state of the art, and allow to exchange high heat fluxes, even more than 12 MW/m 2 , with casting speeds of more than 20 m/min, against the current 6 MW/m 2 , with casting speeds of about 6 m/min. This solution allows to maintain at least the mechanical resistance properties at least of the surface of the mold that is internal during use and in contact with the liquid metal, preventing the onset of cracks. 
     The high heat fluxes that can be removed by the cooling devices according to the present invention allow to at least triple the casting speeds compared to current ones, with the possibility of reaching casting speeds of even more than 20 m/min. 
     Furthermore, the present invention allows to over-size the cooling capacity of crystallizers, both tubular, plate-type or other, by at least 30% more with respect to the necessary, thus allowing to cope with possible unexpected heat loads. 
     Moreover, with the present invention, the interface surface on which the jets are directed is kept constantly cooled to temperatures of about 70° C.−80° C., preventing any problems of the cooling liquid boiling, or the need to put the cooling liquid in the cooling channels or the interspace of a replaceable mold at high pressures. 
     According to a possible solution, the delivery member can be defined by a hole or a tube that connects the feed chamber to the cooling channel. To reduce load losses, the delivery member can have a portion to introduce the liquid that diverges toward the outside, and a portion to discharge the cooling liquid which can be convergent or divergent, i.e. it can have a widening or reduction in the passage section for the liquid. 
     According to a variant, the cooling devices comprise a plurality of delivery members and the feed chamber is configured to feed all the delivery members. 
     The present invention also concerns a method for continuous casting of a liquid metal in a casting cavity defined by at least one wall, which comprises a step of cooling the wall. The cooling step provides the introduction and respectively the discharge of a cooling liquid in at least an interspace, or in one or more cooling channels, associated with the wall, in order to generate a controlled flow of the cooling liquid along the interspace, or along the cooling channels. 
     The cooling step also provides to put the flow of the cooling liquid at a pressure higher than ambient pressure and comprises the delivery of at least one jet of a cooling liquid in the interspace or in the cooling channels, in a delivery direction incident with respect to the controlled flow and against one or more portions of the interface surface of the wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein: 
         FIG. 1  shows in cross section, merely by way of example, a tubular mold for continuous casting according to the current state of the art; 
         FIG. 2 a    is a cross section view of a mold for cast products with a square section; 
         FIG. 2 b    is a section view from B to B in  FIG. 2   a;    
         FIG. 2 c    is a section view from C to C in  FIG. 2   a;    
         FIG. 3  is a longitudinal section view of a mold according to the present invention; 
         FIGS. 4 and 5  are possible views in cross section of the mold in  FIG. 3 ; 
         FIG. 4 a    is a graph that compares the development of the deformation line of the internal surface of a tubular mold according to the state of the art and a possible application of the present invention; 
         FIG. 6  is a longitudinal section view of a possible variant of  FIG. 3 ; 
         FIGS. 7 a  and 7 b    are possible variants of delivery channels according to the present invention; 
         FIGS. 8, 9, 10 and 11  are longitudinal section views of possible variants of  FIG. 3 ; 
         FIGS. 12 and 13  are possible cross section views of the molds as in  FIGS. 8-11 ; 
         FIGS. 14 and 15  are perspective views of a part of a mold according to other variants of the present invention; 
         FIGS. 16 and 17  are cross section views of the mold in  FIG. 15  and according to possible variants; 
         FIG. 18  is a partial perspective view of part of a mold according to a variant of the present invention; 
         FIG. 19  is a sectioned perspective view of an integral mold according to the present invention; 
         FIG. 20  is a sectioned perspective view of a possible variant of  FIG. 19 ; 
         FIGS. 21 and 22  show possible variants of delivery channels according to possible configurations of the present invention; 
         FIGS. 23 and 24  are longitudinal section views of molds according to possible variants of  FIGS. 19 and 20 ; 
         FIGS. 25 and 26  are cross section views of enlarged details of possible variants of the delivery channels applicable to the solutions of  FIGS. 23 and 24 ; 
         FIGS. 27, 28 and 29  are more longitudinal section views of possible variants of  FIGS. 23 and 24 ; 
         FIGS. 30 a , 30 b , 30 c  and 30 d    are plan views of possible cross sections of delivery channels according to possible variants; 
         FIG. 31  is a cross section view of a possible variant of an integral mold according to the present invention; 
         FIG. 32  is a cross section view of a mold for casting slabs; 
         FIGS. 33 a  and 33 b    are possible longitudinal section views along the section line XXXIII-XXXIII in  FIG. 32 ; 
         FIG. 34  is a longitudinal section view along the section line XXXIV-XXXIV in  FIG. 32 ; 
         FIG. 35  is a longitudinal section view of a possible variant of  FIG. 34 ; 
         FIG. 36  is a section view of a possible variant of  FIGS. 3 and 6   
         FIG. 37  is a section view along the line XXXVII-XXXVII in  FIG. 36 ; 
         FIG. 38  is a variant of  FIG. 37 . 
     
    
    
     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 embodiment can conveniently be incorporated into other embodiments without further clarifications. 
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
     With reference to the attached drawings, a mold for continuous casting is indicated in its entirety by the reference number  10  and comprises at least one wall  21  that defines, with a surface  11  that is internal during use, at least part of a casting cavity  22  for the passage of the liquid metal cast. 
     The at least one wall  21  also has an external surface  24 , opposite the internal surface  11 . 
     During use, liquid metal material is introduced into the casting cavity  22  until a determinate level of the meniscus “M” is reached, and then the level of the meniscus M is maintained for the whole casting time. 
     The meniscus M is positioned at a known height, normally comprised between 70 mm and 150 mm, preferably between 80 mm and 140 mm, or between 90 mm and 130 mm with respect to the end edge  35  of the wall  21 . By end edge  35  of the wall  21  we mean the edge in correspondence with which, during use, the liquid metal material is introduced. 
     However, it is not excluded that, in other forms of embodiment, or for particular needs, the meniscus M is positioned at a different height, for example less than 70 mm or higher than 150 mm. 
     Because of the oscillation to which the mold  10  is subjected, in a known manner, the position of the level of the meniscus M with respect to the wall  21  can vary for an amplitude substantially up to the amplitude of the oscillation. Hereafter when we refer to the meniscus M, with respect to the wall  21 , we will therefore refer to an intermediate position thereof, thus comprising the oscillation. Furthermore, referring to the level of the meniscus M correlated to the wall  21 , we intend to refer to the portion of wall  21  that has been suitably designed for positioning the meniscus M. 
     Embodiments of the present invention, for example shown in  FIGS. 3, 4, 5, 12-18 and 31  concern molds  10  of the tubular type for casting billets, blooms, with a round or polygonal section with at least three sides, such as square, rectangular, double T-shaped of the type called beam blanks, U-shaped, sheet piles or similar or comparable sections. 
     According to these embodiments, the molds  10  are defined by one or more walls  21  reciprocally connected with each other to define a tubular body  30  provided with the casting cavity  22 . 
     The walls  21  can be reciprocally connected in a single body, near respective connection portions  36 , as shown in  FIGS. 5, 13-15, 17, 18 and 31  or, according to a solution not shown in the drawings, by using connection means, for example threaded connections and/or external retaining rings. 
       FIGS. 4, 12, 16, 19 and 20  show molds  10  for casting round products comprising a single wall  21 ,  FIGS. 5, 13, 14, 15, 17 and 31  show molds  10  for casting square products comprising four walls  21 , reciprocally connected in a single body, while in  FIGS. 32-34  a mold  10  for casting slabs is partly shown. 
     The present invention can also be adopted, with the usual adaptations as required, for molds with a square section with walls connected by connections of the same size or more than 15 mm. 
     According to one aspect of the present invention, the mold  10  comprises cooling devices  23  to cool the at least one wall  21  by making a cooling liquid flow on one or more interface surfaces portions of the wall  21  on which the cooling liquid flows. 
     In particular, as described in detail hereafter, the portions of interface surface can be defined by the external surface  24 , or part of it, of the wall  21  in the case of a mold  10  of the replaceable type ( FIGS. 3-18 ), or by a plurality of interface surfaces that in turn define a plurality of cooling channels  50  integrated in the wall  21  of an integral mold ( FIGS. 19-31 ). 
     According to the embodiments in  FIGS. 3-18 , we will now describe an application of the present invention to tubular molds  10  of the replaceable type, i.e. provided with one or more walls  21  that can be replaced or renewed, leaving in place the cooling devices  23 . In this case, the wall or walls  21  themselves perform the crystallizer function for the solidification of the molten metal. 
     Hereafter we will refer to a single wall  21  of the mold  10 , but in any case the description can possibly be extended, without further clarifications, to molds  10  provided with several walls  21  as shown in  FIGS. 5, 13, 14, 15, 17, 18 and 31 , where the walls  21  together define a tubular body  30  for casting square products. 
     According to  FIGS. 3, 6, 8, 9, 10 and 11 , the cooling devices  23  comprise a containing body  25  located outside the wall  21  and defining with the latter an interspace  26  in which the cooling liquid passes. 
     The cooling devices  23  comprise introduction members  27  and discharge members  28 , associated in this case with the containing body  25  respectively to introduce and discharge the cooling liquid into and from the interspace  26 , and to generate a controlled flow, under pressure, of the cooling liquid. The flow of cooling liquid is generated between an entrance end and an exit end of the interspace  26 , or of the cooling channels as described hereafter. The entrance end and exit end can be put in correspondence with the upper or lower edge of the mold  10 . 
     The introduction members  27  and discharge members  28  can be positioned so as to generate a flow of cooling liquid in equicurrent ( FIGS. 3, 6, 8, 10, 11 ) or in counter-current ( FIG. 9 ) with respect to the casting direction of the molten metal. The introduction members  27 , or first introduction members, perform the traditional function of feeding the cooling liquid. 
     The flow of cooling liquid has a pressure higher than ambient pressure, i.e. such as to ensure the cooling liquid flows between the introduction members  27  and discharge members  28 , through the interspace  26 . 
     According to a possible solution, the pressure of the flow of cooling liquid at exit from the interspace is at least 1.5 bar or higher. 
     According to a possible embodiment of the present invention, when the cooling liquid flows in equicurrent, the transit speed of the cooling liquid in the interspace  26  is at least 3 m/s or more, while when the cooling liquid flows in counter-current, it is comprised between 10 m/s and 15 m/s. 
     The introduction members  27  and discharge members  28  can be disposed respectively in proximity to the end edge  35  where the liquid metal enters, and in proximity to the edge where the liquid metal exits, or vice versa. 
     The cooling devices  23  according to the present invention comprise at least one delivery member  31  configured to deliver at least one jet G of cooling liquid in a delivery direction incident against the interface surface of the wall  21  with the cooling liquid, in this case with the external surface  24 . 
     The jet G of cooling liquid is provided in the flow of cooling liquid, it generates a perturbation in the flow and optimizes the heat exchange capacity of the cooling liquid with the wall  21 , preventing the formation of insulating limit layers on the external surface  24  of the wall  21 . The jet G, incident toward the external surface  24 , perturbs the flow of cooling liquid, interrupts the formation of the limit layer and generates vortexes in the cooling liquid in the interspace  26  to increase the removable heat fluxes. In fact, thanks to the jet G it is possible to generate a turbulent motion in the interspace  26  to move the super-heated water of the limit layer. 
     Depending on the removable heat fluxes, the jet G can be able to generate a perturbation of the flow of cooling liquid in transit, which as it spreads prevents the formation of the limit layer, or can be delivered so as to pass through the flow of cooling liquid in transit, impact against the surface of the interspace  26  and thus interrupt the formation of the limit layer. 
     The jet G, not the nebulized or spray type, also allows to guarantee a flow rate of the cooling liquid that is sufficiently high and does not cause vaporization of the cooling liquid in contact with the interface surface. 
     The delivery member  31  or delivery members  31  are disposed at least partly inside the interspace  26 . In this way, the cooling liquid introduced by the delivery member  31  is discharged by the discharge elements  28  described above. 
     According to a possible solution, the speed of the jet G exiting from the delivery member  31  is at least two times more than the transit speed of the flow of cooling liquid in the interspace  26 , i.e. in the zone of the interspace  26  where the jet G is delivered. This ensures the at least partial penetration of the jet G into the flow of cooling liquid. 
     Preferably, the speed of the jet G is from two to four times higher than the transit speed of the flow of cooling liquid in the interspace  26 . 
     Merely by way of example, it can be provided that the jet G is delivered toward the external surface  24  of the wall  21 , with a speed comprised between 5 m/s and 100 m/s, preferably between 5 m/s and 70 m/s, even more preferably between 5 m/s and 50 m/s. Applicant has found that already with a delivery speed of the jet G of about 5 m/s, and incident against the external surface  24 , we obtain a cooling of the mold  10  at least three times higher than in conventional solutions where the cooling liquid is made to transit and hit the wall of the mold parallel, with a speed of about 10 m/s. 
     Merely by way of example, Applicant has verified that if it is necessary to remove heat fluxes in the range of 12 MW/m 2 , corresponding to casting speeds of about 20 m/min, the delivery speed of the jet G can also be about 45 m/s, guaranteeing for example a temperature difference of the cooling liquid between entrance and exit to/from the mold  10  of about 10° C. 
     According to the present invention, thanks to the speed of the jet that can possibly also impact against the external surface  24  of the wall  21 , it is possible to keep the latter at extremely low temperatures, for example comprised between 70° C. and 80° C. at every point, thus preventing the boiling of the cooling liquid. 
     It is also possible to obtain this cooling of the external surface  24  by keeping the cooling liquid in the interspace  26  at low pressures, for example pressures at exit from the interspace  26  comprised between 1 bar and 3 bar, and necessary only to guarantee that the cooling liquid flows away to the discharge members  28 . This solution allows to limit the mechanical stresses in the mold  10  due to the pressure of the cooling liquid, increasing the working life of the mold  10 . 
     According to the solution shown in  FIGS. 3-6 and 8-18 , the delivery member  31  can comprise one or more delivery channels  32 , facing toward the external surface  24  of the wall  21  and with a delivery axis incident against the interface surface, in this case against the external surface  24 . 
     According to a possible solution, the delivery channels  32  have a substantially circular cross section shape, through which the cooling liquid passes, although it is not excluded that it can have a different shape, for example square or slit-shaped as described hereafter with reference to  FIG. 18 . 
     In  FIGS. 3 and 8-11 , the delivery channels  32  have their delivery axes substantially orthogonal to the external surface  24 . 
     According to a variant ( FIG. 6 ), the delivery channels  32  have their delivery axes inclined in the direction of transit of the cooling liquid, in this case in the interspace  26 . This solution not only increases the vortex effect of the cooling liquid, but also facilitates the flow of the latter to the discharge members  28 . 
     According to the variant in  FIG. 6 , the delivery channels  32  are disposed inclined with respect to the perpendicular to the external surface  24 , by an angle α which can be comprised between 0° and 30°, preferably between 5° and 15°. 
     According to a possible solution, shown in  FIGS. 7 a  and 7 b   , each delivery channel  32  can be provided at least with an entrance portion  33  in correspondence with which the cooling liquid is introduced, and a discharge portion  34  in correspondence with which the cooling liquid is discharged. 
     The entrance portion  33  can have a flared configuration ( FIG. 7 a   ) or glass-shaped ( FIG. 7 b   ) toward the entrance zone of the cooling liquid to limit the losses of load of the cooling liquid. 
     The discharge portion  34  can have a diameter, or equivalent diameter, of the passage section of the cooling liquid comprised between 1 mm and 8 mm, preferably between 1.5 mm and 4 mm. 
     The discharge portion  34  can also have an extension E, suitable to generate a fall in pressure of the cooling liquid between the entrance and exit of the delivery channel  32  comprised between 1 bar and 12 bar, preferably between 1 bar and 6 bar. 
     Merely by way of example, it is provided that the discharge portion  34  has an extension E of at least 4 mm. This allows to obtain the desired degree of the fall in pressure of the cooling liquid through the delivery channel  32  to confer on the cooling liquid a determinate uniform speed of the jet G toward the external surface  24 . 
     According to the variant shown in  FIG. 7 b   , each delivery channel  32  can be provided with one or more intermediate portions, in this case an intermediate portion with a progressively reduced transit section from the entrance portion  33  to the discharge portion  34 , which allow to progressively increase the speed of the jet G. 
     In  FIG. 3 , the delivery member  31  comprises a plurality of delivery channels  32  disposed distanced from each other to cover a height H of the interface surface, in this case the external surface  24  comprised between 50 mm and 200 mm, preferably comprised between 80 mm and 150 mm. 
     According to a possible variant ( FIGS. 3, 6, 8, 9, 10 and 11 ) the plurality of delivery channels  32  affect the zone of the external surface  24  located around the meniscus M. 
     According to a variant, the sizes of the passage section of the delivery channels  32  can be different as a function of the position that the latter have along the extension in height of the wall  21 . 
     According to a possible solution, the delivery channels  32 , located in the upper part of the wall  21 , can have bigger sizes of the passage section of the cooling liquid than those of the delivery channels  32  disposed below. This solution allows to compensate for the load losses that are gradually generated in the interspace  26 , and ensures that every jet G emitted from the delivery channels  32  impacts on the external surface  24 . 
     According to a variant of the present invention, the first of the delivery channels  32  is located at a distance L ( FIG. 3 ) from the end edge  35  of the wall  21  comprised between 60 mm and 100 mm, preferably between 70 mm and 90 mm. 
     According to another variant ( FIG. 9 ), it can be provided that the delivery channels  32  are reciprocally distanced from each other, in a direction parallel to the casting direction, by a distance that gradually increases as it moves toward the exit end of the cast product. In this way it is possible to obtain a very accentuated distribution of the delivery channels  32  around the meniscus M with respect to the part disposed below. 
     According to the variant shown in  FIG. 4 , the delivery channels  32  are uniformly distributed on the perimeter of the cross section of the wall  21 , to obtain a uniform cooling of the whole circular external surface  24  of the tubular body  30  and at least for said height H. By cross section we mean the section of the wall  21  considered orthogonally to the casting direction of the metal product. 
     Thanks to the high heat flux that the cooling devices  23  according to the present invention are able to remove, it is possible to prevent the formation of a negative taper of the internal surface  11  in proximity to the zone of the meniscus M, and therefore to prevent an insufficient supply of lubricating material on the external surface of the product cast, as described in  FIGS. 1 and 2   c.    
     This statement is confirmed in  FIG. 4 a   , which shows the behavior of the internal surface  11  of the tubular body  30  with crystallizer function, in the current conditions of the state of the art (line A) with a heat flux at the meniscus of 5 MW/m 2 , and in one of the application conditions of the invention (line B), with a heat flux at the meniscus of 8 MW/m 2 . 
     As will be obvious hereafter in the description, Applicant has verified that the deformations identified by lines A and B have a substantially analogous development over the whole circumferential development of the internal surface  11  in the case of molds  10  for casting round products, or in correspondence with the connection portions  36  between walls  21  in the case of casting square products, or polygonal in general. 
     According to the present invention, depending on the results to be obtained and on the sections of the casting cavity  22 , the cooling devices  23  can be sized and designed to obtain that the deformation line around the meniscus M generates an internal surface  11 , with crystallizer function, as much as possible with a taper open toward the end edge  35  of the wall  21  as per line B in  FIG. 4   a.    
     According to the variant shown in  FIG. 5 , the delivery channels  32  are uniformly distributed on the external surface  24  of each of the walls  21  defining the tubular body  30 , at least for said height H ( FIG. 3 ). 
     According to this embodiment, it can be provided that the delivery members  31  are associated only with the external surface  24  of the walls  21 , while the connection portions  36  between the walls  21  are not affected by the jets G, or it can be provided that the delivery members  31  are associated both with the walls  21  and also with the connection portions  36  between the walls  21 . 
     According to the variants shown in  FIGS. 3-6, 8-13 and 16-18 , the delivery members  31  can comprise one or more delivery bodies  37 , with each of which a plurality of the delivery channels  32  are associated. 
     Each delivery body  37  is installed outside the wall  21  and is located facing the interface surface with the cooling liquid, in this case with the external surface  24  of the wall  21 . 
     According to possible solutions, the delivery channels  32  can be made in the thickness of the delivery bodies  37  ( FIGS. 3-6 and 18 ) or they can be supported, for example cantilevered, by the delivery bodies  37  ( FIGS. 8-13, 16 and 17 ). 
     In the variants shown in  FIGS. 3-6 and 18 , the delivery bodies  37  are defined by blocks and/or plates in which the delivery channels  32  are made through in the thickness thereof. 
     According to this embodiment of the present invention, it can be provided that the delivery bodies  37  are distanced from the external surface  24  of the wall  21  by a distance substantially equal to the reciprocal distance between the containing body  25  and the wall  21 , i.e. the sizes of the interspace  26  ( FIG. 3 ). This ensures a uniform transit speed of the cooling liquid along the interspace  26 . 
     According to a variant ( FIG. 6 ), the delivery bodies  37  can be installed distanced from the wall  21  by a first distance D 1  that is less than a second distance D 2  defined between the containing body  25  and the wall  21 . 
     Merely by way of example of the present invention, it can be provided that the first distance D 1  is comprised between about 0.25 and 0.75 times the second distance D 2 . 
     In this way, the delivery bodies  37  define in the interspace  26  differentiated passage sections for the cooling liquid such as to generate, in a first region located above and/or around the meniscus M, higher transit speeds than the transit speed of the cooling liquid in the lower part, for example 100 mm-150 mm under the meniscus M. This solution allows to further increase the efficiency of the heat exchange of the cooling liquid in the zone of maximum heat load. 
     According to a possible variant, not shown in the drawings, each of the delivery bodies  37  is provided only with an array of delivery channels  32  aligned with each other and, during use, positioned parallel to the casting direction. In this case the mold  10  comprises a plurality of delivery bodies  37  disposed distanced from each other to surround the wall  21 . 
     According to another variant, shown in  FIGS. 4 and 5 , the delivery bodies  37  are provided with a plurality of arrays of delivery channels  32  located parallel to each other in a direction substantially orthogonal to the casting direction, to cover at least a surface portion of the external surface  24  that develops along the perimeter of its cross section. 
     According to the variant in  FIG. 4 , a single delivery body  37  is provided, installed to surround the tubular body  30  externally, disposing the delivery axes of the delivery channels  32  incident against the external surface  24  of the wall  21 . 
     According to a possible variant of  FIG. 4 , not shown in the drawings, several delivery bodies  37  can be provided, located one adjacent to the other to surround the tubular body  30  externally. 
     According to the variant in  FIG. 5 , the cooling devices  23  comprise a plurality of delivery bodies  37 , each of which is associated with one of the walls  21  of the tubular body  30 . 
     According to the embodiment shown in  FIGS. 8-13, 16 and 17 , the delivery bodies  37  are defined by a support plate on which the delivery channels  32  are installed protruding cantilevered. This solution allows to position the delivery end of the delivery channels  32  in direct proximity to the external surface  24  of the wall  21 , and prevents any reduction in the usable passage section for the cooling liquid in the interspace  26 . 
     According to a possible variant shown in  FIGS. 3-6, 8-13, 16 and 17 , the cooling devices  23  can comprise at least a feed chamber  38  configured to feed the pressurized cooling liquid to the delivery members  31 . 
     According to this embodiment, the delivery members  31  are interposed between the feed chamber  38  and the interspace  26 , to separate them and allow the cooling liquid, fed into the feed chamber  38 , to pass through the delivery channels  32 . 
     According to this embodiment, the delivery members  31  are at least partly installed in the feed chamber  38 , so as to dispose the entrance portions  33  of the delivery channels  32  facing toward the feed chamber  38 , and the discharge portions  34  of the delivery channels  32  facing toward the interspace  26 . 
     According to a possible solution, the cooling liquid in the feed chamber  38  is pressurized to a pressure comprised between 6 bar and 40 bar, preferably between 10 bar and 30 bar, and is then delivered through the delivery member  31 . The pressure energy of the cooling liquid in the feed chamber  38 , during its passage through the delivery channels  32 , is at least partly converted into kinetic energy of the cooling liquid, which impacts against the external surface  24  of the wall  21 . 
     According to a possible solution, the feed chamber  38  has a volume suitable to stabilize the pressure of the cooling liquid inside it, and to make the pressure value uniform at entrance to all the delivery channels  32 . 
     According to the variants shown in  FIGS. 3, 6, 8 and 11 , the cooling liquid introduction members  27  are directly connected to the feed chamber  38  and are configured to feed the cooling liquid to it. In this embodiment, it is provided that all the cooling liquid in transit in the interspace  26  is fed through the delivery channels  32 . 
     According to the variants shown in  FIGS. 9 and 10 , feed members  39  are connected to the feed chamber  38 , which are independent with respect to the introduction members  27  and configured to introduce the cooling liquid into the feed chamber  38  according to the conditions described above. In this case, both the cooling liquid fed by the introduction members  27  and also the cooling liquid fed by the feed members  39  are made to flow in the interspace  26 , between the containing body  25  and the tubular body  30 . 
     According to this embodiment, the introduction members  27  and the discharge members  28  are independent and distinct from the delivery member  31 , and the latter is installed in an intermediate position between the introduction members  27  and the discharge members  28  along the longitudinal extension of the mold  10 . Therefore, two independent cooling circuits are defined, one to generate the flow parallel to the interspace  26 , and one to generate the at least one jet G. 
     According to a possible variant, shown for example in  FIG. 3  and possibly combinable with the variants described here, the containing body  25  can also be provided with an auxiliary aperture  68  provided in its top part which can be selectively obstructed or connected to cooling liquid introduction members and/or discharge members. This solution allows to use the same containing body  25  to generate a flow of cooling liquid in equicurrent or in counter-current with respect to the casting direction of the liquid metal, depending on the particular connection configuration of the introduction and/or discharge members. 
     According to a possible embodiment of the present invention, the feed chamber  38  can be made in a single body with the external containing body  25  ( FIGS. 3, 6, 8, 9 ), or it can be made as a component, or plurality of separate components associable with the containing body  25  ( FIGS. 10 and 11 ). 
     According to the variant shown in  FIG. 10 , the feed chamber  38  is installed in an aperture  41  made in the containing body  25  so as to position the delivery channels  32  in the interspace  26 . In this case, the feed chamber  38  can be installed selectively removable from the containing body  25 , for example to allow to remove the wall  21  when replacement and/or maintenance is required. 
     According to the variant shown in  FIG. 11 , the feed chamber  38  is installed outside the containing body  25 , and the delivery channels  32  are installed protruding cantilevered, inside the interspace  26 , in holes  44  made in the containing body  25 . This solution allows to position the delivery channels  32  in the interspace  26  with their delivery end in direct proximity to the external surface  24  of the wall  21 . 
     Merely by way of example, it can be provided that the delivery end of the cooling liquid is distanced from the external surface  24  by a distance comprised between 2 mm and 5 mm, preferably about 3 mm. 
     According to a possible variant of the present invention, shown in  FIGS. 6, 8, 9, 13, 15, 36, 37 and 38 , it is provided that the delivery members  31  are connected to positioning members  40  configured to selectively position the delivery channels  32  at predetermined distances from the external surface  24  of the wall  21 . This solution allows to modify the delivery position of the cooling liquid in the interspace  26  and therefore to vary the cooling conditions of the wall  21  as a function of specific design requirements. 
     Furthermore, the positioning members  40  allow to position the delivery members  31  in a position of non-interference with possible movements of the wall  21 , for example required for maintenance operations, or removal of the wall  21 . Merely by way of example, it can be provided that the positioning members  40  are configured to move the delivery members  31  toward/away from the external surface  24  at least by a travel of about 6 mm or more. 
     The positioning members  40  can be chosen from a group comprising threaded connection means, racks, worm screws, linear actuators, articulated mechanisms, motors, sliding guides, or possible combinations thereof. 
     Although not shown in the drawings, the positioning members  40  can also be associated with the delivery members  31  of the solutions in  FIG. 3, 4, 5, 10, 11, 12, 16 or 18 . 
     According to a possible variant, shown in  FIGS. 3 and 8 , the delivery members  31  can also be provided with auxiliary cooling liquid supply channels  42 , configured to ensure the supply of a desired delivery of cooling liquid in the interspace  26 . 
     The auxiliary supply channels  42  can be defined for example by through holes and/or apertures made in the delivery body  37  that separates the feed chamber  38  and the interspace  26 . 
     Merely by way of example, the auxiliary supply channels  42  can have a diameter, or equivalent diameter, comprised between 4 mm and 6 mm. 
     According to the variants shown in  FIGS. 6, 8-13 , the external surfaces  24  of the walls  21  are provided with a plurality of longitudinal grooves  43 , made in the thickness of the latter, substantially parallel to the casting direction of the metal material and which extend longitudinally in a zone around where the meniscus M is located. The delivery members  31  can be installed in correspondence with the longitudinal grooves  43  made in the walls  21 . 
     The longitudinal grooves  43  allow to reduce the heat resistance opposed by the wall  21  and which the cooling liquid meets due to the heat exchange toward the internal surface  11  of the wall  21 . The longitudinal grooves  43  reduce the distance between the internal surface  11  and the interface surface with the cooling liquid, in this case the external surface  24 . This allows to increase the heat exchange between the molten metal and the cooling liquid. 
     According to a variant ( FIG. 6 ), it can be provided that the longitudinal grooves  43  are made starting from a height K from the end edge  35  which is comprised between 50 mm and 150 mm. 
     According to another variant, ( FIG. 6 ), it can be provided that the longitudinal grooves  43  have a length T comprised between 50 mm and 300 m, although for some variants, applicable for example to molds for billets, the length T can be equal to or more than 500 mm, and extend for the whole length of the mold. 
     For molds suitable to cast round products, the longitudinal grooves  43  can have a length T comprised between 80 mm and 180 mm, while for molds  10  suitable to cast square products, the longitudinal grooves  43  can have a length T comprised between 150 mm and 300 mm. 
     According to the variants in  FIGS. 6, 12 and 13 , the longitudinal grooves  43  have a depth P in the thickness of the wall  21  that is uniform along its longitudinal extension, although it is not excluded that the longitudinal grooves  43  can have a different depth along the longitudinal extension of the wall  21 , as shown in  FIGS. 8-11 , where the depth P is greater in the zone around the meniscus M, compared with the zones below. 
     In particular, the depth P of the longitudinal groove  43  can be linearly increasing toward the exit end of the metal product ( FIG. 11 ), or increasing in a curvilinear manner toward the end edge  35  ( FIG. 8 ), or with segments having a depth gradually increasing toward the end edge  35  ( FIGS. 9 and 10 ). 
     The longitudinal grooves  43  can have a depth P comprised between 2 mm and 8 mm, preferably between 5 mm and 7 mm. 
       FIG. 12  shows embodiments of a mold  10  for casting products with a round section or square section having a radius of curvature in the edge between walls  21  comprised between 15 mm and 40 mm. 
     The longitudinal grooves  43  can have an amplitude A ( FIGS. 12 and 13 ) comprised between 5 mm and 12 mm and be reciprocally distanced by about 5-10 mm. 
     According to a variant, shown in  FIG. 14 , the at least one wall  21  can be provided with one or more transverse grooves  45 , made transverse to the oblong development of the wall  21 , that is, in this case orthogonally to the casting direction, and which can extend for the entire extension in width of the wall  21 . 
     According to a variant, not shown, it can be provided that the transverse grooves  45  are made on the walls  21  of a tubular body  30  with a screw or spiral development, single or multi-start, along at least part of the longitudinal extension of the tubular body  30 . 
     The transverse grooves  45 , in the same way as described above for the longitudinal grooves  43 , allow to reduce the heat resistance opposed by the wall  21  and which the cooling liquid meets due to the heat exchange toward the internal surface  11  of the wall  21 . 
     According to the embodiment in  FIG. 14 , where the walls  21  define the tubular body  30 , the transverse grooves  45  extend continuously along the whole perimeter development of the cross section of the tubular body  30 . 
     A greater density in the distribution of the transverse grooves  45  can also be provided in the zone around the meniscus M compared with the zone disposed below. 
     The transverse grooves  45  can have a depth W comprised between 2 mm and 8 mm, preferably between 5 mm and 7 mm. 
     The transverse grooves  45  made in correspondence with the meniscus M can have a depth W greater than that of the transverse grooves  45  located below the level of the meniscus M. 
     The transverse grooves  45  have an amplitude E ( FIG. 14 ) comprised between 5 mm and 12 mm and can be reciprocally distanced by about 5-10 mm. the transverse grooves  45  around the meniscus M can have a smaller amplitude E compared with the transverse grooves  45  located in a zone below the meniscus M. 
     The delivery members  31  can be installed in correspondence with each of the transverse grooves  45  to deliver jets G of cooling liquid incident against the internal surface of the transverse grooves  45 , which prevent the generation of dead zones where the cooling liquid is stabilized and does not allow an efficient heat exchange. 
     According to some embodiments, not shown, it is not excluded that the wall  21  is provided with both longitudinal grooves  43  and transverse grooves  45 . 
     According to a variant shown in  FIG. 15 , the at least one wall  21  can be provided with a reduction in thickness  46  made at least in a zone comprised around the meniscus M and which extends toward a zone below, for example for an extension B comprised between 50 mm and 150 mm. In this case too, the reduction in thickness  46  has the function of reducing the heat resistance between the metal cast and the cooling liquid in circulation. 
     According to the variant shown in  FIGS. 15 and 16 , the reduction in thickness  46  extends for the entire perimeter development of the cross section of the tubular body  30 , although it is not excluded that the reduction in thickness  46  can be made only in the walls  21 , and does not affect the connection portions  36 , as shown for example in  FIG. 17 . 
     According to the variants in  FIGS. 16 and 17 , it can be provided that the delivery members  31  are installed directly in proximity to the reduction in thickness  46 , bringing the delivery end of the delivery channels  32  nearer to the external surface  24  defined in this case by the bottom of the reduction in thickness  46 . 
     According to the variant in  FIG. 18 , a possible variant is shown of the delivery member  31 , applied in this case to a wall  21  of a tubular body  30 , which is provided with a plurality of delivery channels  32  configured as slits and made in the delivery body  37 . This variant can possibly be combined with all the variants described here. The delivery channel  32 , configured as a slit, allows to generate a blade-type jet G of cooling liquid, which is conveyed against the external surface  24  of the wall  21  in an incident direction. Furthermore, a delivery channel  32  configured as a slit can be made simply and quickly. 
     Each delivery channel  32  can extend longitudinally as a slit for a length comprised between 5 mm and 150 mm, to affect a wide development in length of the external surface  24 . 
     According to the variant shown in  FIG. 18 , the delivery channels  32  can have a width comprised between 1 mm and 3 mm, also chosen as a function of the desired fall in pressure required for the cooling liquid. 
     According to the variant shown in  FIG. 18 , the delivery channels  32  are disposed substantially parallel to the casting direction, even though, according to a variant, the delivery channels  32  can be positioned at different angles, for example orthogonally to the casting direction. 
     For clarity of exposition,  FIG. 18  does not show the feed chamber  38  of the cooling liquid, although its presence is not excluded, as described above. 
       FIGS. 19-31  show possible variants of molds  10  of the integral type, i.e. provided with the cooling devices  23  at least in part of their thickness. 
     According to the embodiments in  FIGS. 19-31 , the cooling devices  23  comprise a plurality of cooling channels  50  made in the thickness of the wall or walls  21 . 
     The cooling channels  50  can be made parallel to the longitudinal development of the wall  21 , i.e. substantially parallel to the casting direction. 
     Merely by way of example, the cooling liquid in the cooling channels  50  can have a pressure of at least 1.5 bar, and sufficient only to guarantee that the cooling liquid flows through the cooling channels  50 . 
     According to a possible solution, the cooling channels  50  are connected to the introduction members  27  and the discharge members  28 , to generate a flow of cooling liquid along the longitudinal extension of the cooling channel  50 , in equicurrent or counter-current with respect to the casting direction of the liquid metal, using methods substantially analogous to what was described above with reference to the interspace  26 . It is quite clear that all the embodiments described above regarding the delivery of jets G in the interspace  26  can be adopted and combined, with simple adaptations, to the embodiments described hereafter for the cooling channels  50 . 
     According to the variant shown in  FIGS. 19-31 , the cooling devices  23  comprise delivery members  31  integrated in the thickness of the wall  21  and configured to deliver at least one jet G of cooling liquid inside at least some of the cooling channels  50  in a direction incident against at least a surface portion that defines the cooling channels  50 . 
     The methods and parameters used to deliver the jet G are substantially analogous to those described above with reference to the delivery of the jet G in the interspace  26 . 
     In particular, the jet G is directed toward the surface portion of the cooling channels  50 , also called “water hot face”, which is located at the smallest distance from the internal surface  11  of the wall  21 . 
     For this solution too, thanks to the presence of at least one jet G as defined above, it is possible to keep the internal surface of the cooling channels  50  at a temperature lower than 70° C.-80° C. as described above, and to prevent putting the cooling liquid in the cooling channels  50  at high pressure. 
     The delivery member  31  can be put in an intermediate position between the introduction members  27  and the discharge members  28  as shown in  FIGS. 28 and 29 , and can be a separate and distinct component with respect to the latter. 
     According to a variant, shown in  FIGS. 19, 20, 23, 24 and 27 , the introduction members  27  can be associated with the delivery members  31  so that the introduction of the cooling liquid into the cooling channel  50  takes place only through the delivery member  31 . 
     In  FIGS. 19 and 20 , the delivery members  31  comprise delivery channels  32 , each of which is made through in the thickness of the wall  21 , in a transverse direction with respect to the oblong development of the cooling channels  50 , from the external surface  24  of the latter, until it intercepts one of the cooling channels  50 . 
     According to  FIG. 19 , an array of delivery channels  32  are associated with each cooling channel  50 , and are aligned with each other in a direction parallel to the longitudinal extension of the cooling channels  50 . 
     It is also provided that the delivery channels  32  can have a configuration and disposition substantially analogous to those described above with reference to the application on the integral walls  21  as in  FIGS. 3-18 . 
     According to  FIG. 20 , a delivery channel  32  is associated with each cooling channel  50 , made in the thickness of the wall  21  and having a slit configuration to emit a blade-shaped jet G. The slit configuration of the delivery channel  32  can be substantially analogous to that described above with reference to  FIG. 18 . According to this embodiment, the presence can be provided of one or more delivery channels  32  for each cooling channel  50 . 
       FIG. 21  shows a possible disposition of the delivery channel  32  having its delivery axis substantially centered and intersecting the axis of longitudinal development of the cooling channel  50 . This solution allows to generate turbulence inside the cooling channel  50  and to keep the hottest surface portion of the cooling channel  50  constantly cooled by the jet G of cooling liquid. 
     In  FIG. 22 , the delivery channel  32  is made so as to dispose the delivery axis of the cooling liquid tangent on the periphery of the surface defining the cooling channel  50 . This solution generates, in the cooling channel  50 , a vortex effect on the cooling liquid that propagates along a large part of the longitudinal extension of the cooling channel  50 . 
       FIGS. 23 and 24  show possible variants in which the delivery members  31  comprise one or more delivery bodies  37 , with each of which a plurality of delivery channels  32  are associated. 
     In particular,  FIG. 23  shows a possible variant in which the delivery channels  32  are made in the thickness of the delivery body  37 , in substantially the same way as described above with reference to  FIGS. 3-6 . According to this variant, the wall  21  is provided with a plurality of apertures or eyelets  51 , each made through, in the direction of the thickness of the wall  21 , toward one of the cooling channels  50  to allow to position one of the delivery bodies  37  through it, and to adjust the distance between the delivery end of the delivery channels  32  and the surface defining the cooling channel  50 . 
       FIG. 24  instead shows a variant in which the delivery channels  32  are supported cantilevered by the delivery body  37 , in substantially the same way as described above with reference to  FIGS. 8-15 . 
     According to this variant, in correspondence with each cooling channel  50  a plurality of through holes  52  are made in the thickness of the wall  21 , from its external surface  24  until it intercepts the respective cooling channel  50 . 
     Each delivery body  37  is installed outside the wall  21  and is located facing one of the cooling channels  50  to deliver the cooling liquid against a surface portion of the latter. 
     In this embodiment of the present invention too, the delivery channels  32  made and/or provided in the delivery body  37  as in the solution in  FIGS. 23 and 24  can be installed in the wall  21  so as to position the delivery axes of the cooling liquid centered with the longitudinal axis of the cooling channel  50  ( FIG. 25 ) with the effects described with reference to  FIG. 21 , or positioned tangent on the periphery of the cooling channel  50  ( FIG. 26 ) with the effects as described with reference to  FIG. 22 . 
     Furthermore, the continuous delivery of the jets of cooling liquid against the internal surface portion of the cooling channels  50  that is located at the least distance from the internal surface  11  of the wall  21  allows to move toward the rear part of the cooling channel  50  the flow of cooling liquid that has impacted on the surface of the cooling channel  50  and has heated up. This allows to supply, in the impact zone of the jet G, cooling liquid that is always cold, and therefore allows to optimize heat exchange. 
     According to possible embodiments of the present invention, the delivery members  31  can also comprise a feed chamber  38  to feed the cooling liquid, in substantially the same way as described above with reference to  FIGS. 3-6, 8-15 . 
     Furthermore, in the same way as described above with reference to  FIGS. 6, 8, 9, 13 and 17 , positioning members  40  can be associated with the delivery bodies  37 , to modify the position of the delivery channels  32  inside the cooling channels  50  and to modify the distance between the delivery end and the interface surface of the cooling channels  50 . 
     According to the variant shown in  FIG. 23 , it can be provided that at least one of the cooling channels  50  has sizes of its diameter, or equivalent diameter, that are different along its longitudinal extension. For example, it can be provided that the cooling channels  50  have a first portion  53  located near the end edge  35  with a first diameter D 1 , and at least a second portion  54 , consecutive to the first portion  53 , having a second diameter D 2 , less than the first diameter D 1 . Merely by way of example, the first portion  53  can extend substantially from the end edge  35  for a height comprised between 150 mm and 250 mm. 
     The delivery member  31  is installed during use in correspondence with each first portion  53 . The difference in size of the first portion  53  compared with the second portion  54  allows to house the delivery ends of the delivery channels  32  at least partly inside the cooling channel  50 . 
     This solution, although described with reference to  FIG. 23 , can be adopted, with the usual adaptations as required, to the variants described here. 
     In the same way as described above with reference to  FIGS. 3 and 8 , the delivery members  31  can also be provided with auxiliary supply channels  42  for the cooling liquid, configured to ensure the supply of a desired delivery of cooling liquid in each cooling channel  50  as shown in  FIGS. 19, 23 and 24 . 
     According to the variant shown in  FIG. 27 , the delivery members  31  associated with each cooling channel  50  comprise delivery channels  32  configured to emit a blade-type jet G. In particular, at least one first delivery channel  32  is provided positioned above or around the meniscus M, and at least one second delivery channel  32  positioned under the meniscus M. Merely by way of example, it can be provided that the second delivery channel  32  is positioned at a distance from the meniscus M comprised between 80 mm and 150 mm. The first and second delivery channel  32  can be disposed centered or in a tangential position in the cooling channel  50  as described with reference to  FIGS. 25 and 26 . 
     This solution allows to introduce into the upper part of the wall  21  a first jet G of cooling liquid to cool the zone located around the meniscus M, and to introduce through the second delivery channel  32  a second jet G of fresh cooling liquid to optimize the cooling of the part below. The cooling liquid is then discharged from the cooling channels  50  near the exit end of the metal product and through the discharge members  28 . 
     According to a possible variant, not shown in  FIG. 27 , the first delivery channel  32  positioned above or around the meniscus M has a section to deliver the cooling liquid that is larger than the second delivery channel  32  positioned under the meniscus M. 
     The first and second delivery channels  32  can be inserted through respective apertures  51  made in the thickness of the wall  21  and toward the cooling channels  50 . Furthermore, as described above, the delivery members  32  can also be associated with feed chambers  38  of the cooling liquid. The feed chambers  38  can in turn be connected to feed members  39  as described above, independent of the introduction members  27 . 
     In the same way as described above with reference to  FIG. 23 , in the variant shown in  FIGS. 27 and 28  too, the cooling channels  50  can have a first portion  53  and a second portion  54  with different diameters. According to this solution, a variant can be provided, possibly combinable with the variants described here, in which the surface of the cooling channel  50  defining the first portion  53  is distanced from the internal surface  11  of the wall  21  by a first distance K 1  and the surface defining the second portion  54  is distanced from the internal surface  11  by a second distance K 2 , smaller than the first distance K 1 . This solution allows to reduce the thickness of the wall  21  to be cooled in the first portion  53  where the heat fluxes are extremely high, and consequently guarantees an efficient heat exchange with the cooling liquid. 
     The variants in  FIGS. 28 and 29  show possible variants of  FIG. 27 , where for each cooling channel  50  there is a single delivery channel  32 . 
     In particular, in the variant of  FIG. 28 , the delivery channel  32  is made as a separate element from the wall  21  and is installed in the wall  21  in correspondence with an aperture  51  made in the latter and communicating with one of the cooling channels  50 . 
     On the contrary, in the variant of  FIG. 29 , the delivery channel  32  is inserted through in the thickness of the wall  21  and can be configured to deliver a jet G, blade-like or directed toward a point, against the internal surface of the cooling channel  50 . 
     According to a possible variant, the delivery channel  32  can be positioned at a distance from the end edge  35  comprised between 150 mm and 300 mm. In this case the cooling liquid is made to circulate in the cooling channel  50  in counter-current with respect to the casting direction. 
     According to the variants shown in  FIGS. 30 a , 30 b , 30 c  and 30 d   , combinable with all the embodiments described here, the delivery channel  32  can have a cross section shape for the passage of the cooling liquid configured as an elongated eyelet, with a section defined by two consecutive holes ( FIG. 30 a   ), with an ellipsoidal eyelet ( FIG. 30 b   ), a rectangular section ( FIG. 30 c   ), or with a circular section ( FIG. 30 d   ). 
     According to the variants in  FIGS. 28 and 29 , the delivery channel  32  is installed in the cooling channel  50  at a distance from the end edge  35  comprised between 200 mm and 500 mm. 
     According to possible variants not shown in the drawings, it is possible to provide two, three, four or more delivery channels  32  for each cooling channel  50 , disposed along the longitudinal development of the latter to generate vortexes in the cooling liquid substantially extended along the entire length. 
     Although  FIGS. 19-29  show a wall  21  of the integral type, made in a single body, possible variants are not excluded, for example shown in  FIG. 31 , in which the wall  21  is obtained by connecting several wall elements, for example a first wall element  55  and a second wall element  56 . 
     The first wall element  55  and the second wall element  56  can be defined by one or more plates or by one or more tubular elements, for example one disposed inside the other. 
       FIG. 31  shows possible variants of a wall  21  in which the first wall element  55  and/or the second wall element  56  are provided, in correspondence with their interface connection surfaces  57 , with respective grooves  58 . When the first wall element  55  and the second wall element  56  are in their coupled condition, the grooves  58  define the cooling channels  50  for the passage of the cooling liquid. 
     According to this embodiment of  FIG. 31 , it is provided that the delivery members  31  are associated at least with the wall element located outermost, in this case with the first wall element  55 , according to one or other of the methods described above. 
     According to one of the variants shown in  FIG. 31 , it can also be provided that, in the direction of the cross section, two or more delivery channels  32  are also associated with each cooling channel  50 . 
     According to possible solutions, the cooling channels  50  can be made substantially parallel to the casting direction or orthogonal to the casting direction, or a combination thereof. 
     It is quite evident that all the variants described here can be adopted for both molds of the tubular type and also molds of the plate type, i.e. for the production of any metal product whatsoever with a desired section as identified above, not excluding an application of the present invention to molds for slabs, including conventional slabs, thick slabs, thin slabs and ultrathin slabs. 
       FIGS. 32, 33   a ,  33   b ,  34  and  35  show some possible variants of a plate-type mold  10  suitable to cast slabs. 
     According to the variants shown in  FIGS. 32-34 , the mold  10  comprises a plate  59 , defining the wall  21  described above, with a crystallizer function, and a counter-plate  60  attached to the external surface  24  of the wall  21 . 
     In particular, the counter-plate  60  is located resting on the plate  59  and is attached to it by means of connection devices  61  which, in this case, comprise threaded elements  62 . 
     According to the variant in  FIGS. 32 and 34 , the threaded elements  62  comprise a screw inserted in a through hole  63  made in the counter-plate  60  and screwed into a threaded hole  64  provided in the plate  59 . Other embodiments can provide to use studs or threaded bushings attached to the plate  59 . 
     In a known manner, grooves  65  are made in the thickness of the plate  59 , open toward the external surface  24  of the plate  59 , and which according to a possible solution not shown in the drawings can be closed directly by the counter-plate  60 , or closed by closing elements  66  such as blades inserted in part of the depth of the grooves  65 . 
     Together with the counter-plate  60  and/or the closing elements  66 , the grooves  65  define the cooling channels  50  for the passage of the cooling liquid. 
     The grooves  65 , and consequently the cooling channels  50 , can be made substantially parallel to the casting direction, or orthogonal to the casting direction, or a combination thereof, for example according to a substantially analogous disposition to that described above with reference to  FIG. 14 . 
     According to the variant in which the grooves  65  have an oblong development in a direction orthogonal to the casting direction, the grooves  65  are made without a break in continuity along their longitudinal development. This prevents the creation of portions of plate  59  having greater structural rigidity than other portions and of irregularities in the internal surface  11  of the plate  59 . 
     The grooves  65  can have a substantially rectangular cross section shape, with a flat and/or rounded bottom surface, the section not being restrictive for the purposes of the present invention. 
     The closing elements  66  have a closing surface of the grooves  65  which defines the cooling channel  50 , which has a flat or curved development to define cooling channels  50  with a cross section that is circular, rectangular, or with rounded edges as shown in  FIG. 32 . 
     According to this embodiment, the delivery members  31  are associated with the plate  59  to deliver, in the cooling channels  50 , jets G in a direction incident against the bottom surface of the grooves  65 . 
     In particular, as shown in  FIGS. 32, 33   a  and  33   b , it is provided that the delivery members  31  comprise delivery channels  32  associated with the closing elements  66  of the grooves  65  ( FIG. 33 b   ) and/or made directly in the thickness of the closing elements  66  ( FIG. 33 a   ), according to methods and/or dispositions substantially analogous to what we described above with reference to  FIGS. 3, 6, 7   a ,  7   b ,  18 ,  23 ,  25 ,  26 ,  27 ,  28 ,  29 ,  30   a ,  30   b ,  30   c ,  30   d.    
     According to the variant in  FIG. 33 b   , the delivery channels  32  are associated with delivery bodies  37  installed in the thickness of the closing elements  66 , to dispose the discharge portions of the delivery channels  32  inside the cooling channels  50 , at a predetermined distance from the bottom of the groove  65 . 
     To this purpose, the delivery channels  32  can be associated with the delivery bodies  37  according to methods substantially analogous to what we described above with reference to  FIGS. 3, 6, 8, 9, 10, 11, 18, 23, 24 . 
     According to the variant in  FIG. 33 b   , the delivery bodies  37  are installed through an aperture made in the closing elements  66 . 
     According to the variants in  FIGS. 32, 33   a ,  33   b , the counter-plate  60  can be provided with one or more apertures  67  to allow to install feed chambers  38  for the cooling liquid to the delivery channels  32  in the same way as described above. 
     If the grooves  65  are directly closed by the counter-plate  60 , according to a variant not shown in the drawings, it can be provided that the delivery members  31 , with the respective delivery channels  32 , are installed and/or made directly in the counter-plate  60 , to create the jets G in the cooling channels  50 . 
     According to the variant shown in  FIGS. 32 and 34 , the plate  59  can be provided in its thickness with cooling channels  50  of a substantially circular shape, made in direct proximity to the connection devices  61 , preventing the formation of surface cracks on the plate  32 . 
     According to the variants in  FIGS. 32 and 34 , delivery members  31  can also be associated with the cooling channels  50  with circular section made in correspondence with the connection devices  61 , and are provided to deliver jets G of cooling liquid in the cooling channels  50 . 
     According to this embodiment, it can be provided that the delivery members  31  are installed in an intermediate position between two or more connection devices  61  as shown in  FIG. 34 . 
     For this variant too, it can be provided that the delivery members  31  are associated directly with the plate  59  ( FIG. 35 ), or are associated with the counter-plate  60  ( FIG. 34 ), for example in correspondence with apertures  67  made in the latter as described above with reference to  FIG. 33 . 
     The delivery channels  32  associated with the cooling channels  50  with a circular section can be made directly in the thickness of the plate  59 , or they can be installed or made in delivery bodies  37  to be installed on the plate  59 . 
     Furthermore, the delivery channels  32  can be associated with the cooling channels  50  according to installation modes and/or configurations substantially analogous to what we described above with reference to  FIGS. 19-29 , possibly attaching the feed chamber  38  either directly to the wall  21 , or to the counter-plate  60 . 
     In the same way, the dispositions of the delivery channels  32  described in the embodiments in  FIGS. 27, 28 and 29  can be adopted with the due modifications for molds for slabs, in which the delivery channels  32  are associated and/or made in the closing elements  66  of the grooves  65 , or in the plate  59 . 
     For example, with reference to  FIG. 35 , a possible variant is shown in which the delivery channels  32  are made protruding cantilevered on a delivery body  37  and, in the same way as described above with reference to  FIG. 24 , are inserted into through holes  52  made in the wall  21  and intercepting one of the cooling channels  50 . In this case, the delivery channels  32  have a configuration substantially analogous to that described with reference to  FIG. 7 b   , that is, they are provided with at least one entrance portion  33  and a discharge portion  34 . 
     According to the variants described in  FIGS. 33 a  and 33 b   , the cooling channels  50  have cross section sizes for the passage of the cooling liquid that are variable along the longitudinal extension. In particular it is provided that the zone of the cooling channels  50  located around the delivery members  31  has section sizes bigger than a zone disposed below. 
     According to the variant shown in  FIG. 33 a   , the grooves  65  have a first portion  69  located between the end edge  35  and a zone around which the meniscus M is positioned, defining a first thickness W 1  between the bottom of the groove  65  and the internal surface  11 , and a second portion  70  located consecutive to the first portion  69  and defining a second thickness W 2  between the bottom of the groove  65  and the internal surface  11 , bigger in size than the first thickness W 1 . 
     It is clear that modifications and/or additions of parts may be made to the mold  10  and casting method as described heretofore, without departing from the field and scope of the present invention. 
     For example, with reference to  FIGS. 36, 37 and 38 , a possible variant is described to the solutions described with reference to  FIGS. 3 and 6 , in which the delivery body  37  defines at least part of the containing body  25  and therefore delimits the interspace  26 . The delivery body  37  is provided with the delivery channels  32  disposed according to one and/or another of the methods described above. 
     The positioning members  40  in this case not only move the delivery body  37  toward/away from the external surface  24 , but also allow to adjust the sizes of at least part of the interspace  26 , so that in this way it is possible to control the transit speed of the cooling liquid. In this embodiment, therefore, thanks to the positioning members  40  it is possible on the one hand to adjust the position of the delivery members  31  and on the other hand to control the sizes of the interspace  26 , also possibly to facilitate the removal of the wall  21  during the replacement operations. 
     The delivery body  37  according to this embodiment can affect only part of the containing body  25  as shown in  FIG. 36 , or it can affect its whole longitudinal extension: in this way it is possible to adjust the sizes of the interspace  26  along the whole length of the wall  21 . 
     According to  FIGS. 36 and 37 , the delivery body  37  can be provided with at least a protruding portion  70  in correspondence with which the delivery channels  32  are made, selectively positionable, possibly, in longitudinal grooves  43  made in the wall  21  as shown in  FIG. 38 . 
     According to  FIGS. 36-38 , the delivery body  37  is associated with the feed chamber  38  which is in turn connected to the introduction members  27  and is provided to feed the cooling liquid to the delivery members  31  and possibly to an auxiliary feed hole made in the containing body. 
     It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of mold  10  and casting method, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.