Bottom block for a semi-continuous metal casting mold system

Abstract

The invention concerns a bottom block (10) for a continuous metal casting mold system (1) comprising a main body (30) comprising a main surface (31) adapted to receive the metal to be casted; and a peripheral ledge (50) defining a closed edge encircling the main surface (31), and protruding from the main surface (31) along a casting direction (Z), the peripheral ledge (50) comprising side walls (51); at least one side wall (51) comprising an enlarged portion (53), said enlarged portion (53) presenting an enlarged width (w53) counted perpendicular to the casting direction (Z) which is strictly superior to a largest width (w51) of the rest of said at least one side wall (51). The invention also concerns a system (1) for casting metal comprising such bottom block (10).

Description

[0001] DESCRIPTION

[0002] TITLE: BOTTOM BLOCK FOR A SEMI-CONTINUOUS METAL CASTING MOLD SYSTEM

[0003] TECHNICAL FIELD OF THE INVENTION

[0004] This invention relates to the field of semi-continuous metal casting, in particular aluminum alloys casting, and more particularly to bottom blocks used to start metal ingot casting in continuous metal casting systems.

[0005] BACKGROUND

[0006] Manufacturing metal ingots is a first step to obtain end products made of metal. One method of manufacturing an ingot is through a semi-continuous casting process, whereby a vertically oriented mold cavity is situated above a platform that translates vertically down. A bottom block may be situated on the platform and form a bottom of the mold cavity, at least initially, to begin the casting process. Molten metal is poured into the mold cavity whereupon the molten metal cools and the solidification process begins, typically using a cooling fluid, typically water, in the DC (Direct-Chill) configuration.

[0007] Some semi-continuous casting systems may include an electromagnetic field used to shape the ingot, while avoiding any contact with the walls of the frame used to shape the ingot. When using such type of metal casting, the cooling water may first cool the walls of the frame, and then enter in contact with the solid skin of the metal ingot being casted.

[0008] Whatever the casting technique used, the platform with the bottom block thereon may descend into the casting pit at a predefined speed to allow the metal exiting the mold cavity and descending with the bottom block to solidify. The platform continues to be lowered as more molten metal enters the mold cavity, and solid metal exits the mold cavity. This semi-continuous casting process allows metal ingots and billets to be formed according to the profile of the mold cavity or the frame, and having a length limited only by the casting pit depth and the hydraulically actuated platform moving therein.

[0009] However, during the life-cycle of a bottom block, it has been noticed that the upper perimeter of the block experiences continual damage. The type of damage observed are “dents” which reduce the “block’s dish capacity” to retain molten metal at the start of a cast.

[0010] As a result, molten metal overflows at low spots (caused by the dents) and then solidifies to form a “finger(s)” in the bottom of the ingot. Besides, with each casting cycle, the damage continues, and dents are growing deeper and fingers extend longer. At some point, the size and number of finger(s) in the ingot butt becomes locked or keyed to the bottom block. This restricts the natural bottom curl during the ingot shell formation and during solidification stage.

[0011] Therefore, there is a need for eliminating and reducing the extent and rate of bottom block damage (dents). SUMMARY OF THE INVENTION

[0012] The present invention aim at solving the aforementioned problems. To this end, the invention concerns a bottom block for a semi-continuous metal casting mold system comprising: a main body comprising a main surface adapted to receive the metal to be casted; a peripheral ledge defining a closed edge encircling the main surface, and protruding from the main surface along a casting direction, the peripheral ledge comprising side walls; at least one side wall comprising an enlarged portion, said enlarged portion presenting an enlarged width counted perpendicular to the casting direction which is strictly superior to a largest width of the rest of said at least one side wall.

[0013] The provisions previously described allows designing a bottom block for a semi-continuous casting mold system with a peripheral ledge presenting an improved mechanical resistance.

[0014] According to an embodiment, the bottom block comprises on or more of the following features, taken alone or in combination.

[0015] According to an embodiment the metal comprises aluminum and is preferentially an aluminum alloy.

[0016] According to one embodiment, a ratio of the enlarged width over the largest width of the rest of said at least one side wall is at least 1 .1 , 1 .5, 2.0, 2.5, or 3.0.

[0017] According to one embodiment, the enlarged width is comprised between 25.5 mm and 51 .0 mm, and notably sensibly equal to 42.0 mm.

[0018] According to one embodiment, the at least one side wall comprises a pair of facing longitudinal side walls and a pair of lateral side walls defining a quadrilateral closed edge of the peripheral ledge, each longitudinal side wall comprising an enlarged portion presenting an enlarged width counted perpendicular to the casting direction which is strictly superior to a largest width of the rest of said longitudinal side wall.

[0019] Thus, it is possible to reinforce mechanically the longitudinal side walls which are usually more constraint by the liquid metal than the lateral side walls.

[0020] According to one embodiment the enlarged width is inferior to 70 mm, more particularly to 60 mm and preferably inferior to 50 mm.

[0021] According to one embodiment the enlarged width is superior to 10 mm.

[0022] According to one embodiment, the closed edge of the peripheral ledge is sensibly rectangular.

[0023] Thus, it is possible to cast ingots with a sensibly rectangular cross-section, the bottom block being then adapted to limit the formation of dents in the peripheral ledge of the bottom block.

[0024] According to one embodiment, the enlarged portion presents an enlarged portion length counted along an extension direction of the at least one side wall in which said enlarged portion is included, said enlarged portion length being comprised between 35 cm and 60 cm, preferably between 40 cm and 50 cm, and preferentially typically equal to about 45 cm. According to one embodiment, the enlarged portion includes a center of the at least one side wall.

[0025] According to one embodiment, the enlarged portion presents a symmetrical shape compared to the center of the side wall in which said enlarged portion is included

[0026] Thus, it is possible to avoid any dissymmetrical shape in the final ingot.

[0027] For example, the enlarged portion presents a general rectangular shape centered in the middle of the length of the side wall.

[0028] According to one embodiment, each longitudinal side wall presents a longitudinal length counted along a longitudinal direction perpendicular to the casting direction and to the enlarged width, and wherein each enlarged portion presents an enlarged portion length counted along the longitudinal direction; a ratio of the longitudinal length over the enlarged portion length being comprised between 1 .5 and 6.0, preferentially between 2.0 and 5.5, and more preferentially between 2.5 and 5.0.

[0029] This arrangement is a good compromise to reduce damages on the bottom block along with allowing good casting.

[0030] According to one embodiment, the main surface comprises a curved zone, a curvature of said curved zone being convergent towards the peripheral ledge.

[0031] Thus, when the bottom block is filed with molten metal, the filling of the bottom block is realized from the center of the main surface, and towards the peripheral ledge.

[0032] According to one embodiment, the curved zone comprises a border zone defined adjacent to the enlarged portion, said border zone presenting a radius of curvature which is strictly inferior to a lowest radius of curvature of the rest of the curved zone.

[0033] Thus, it is possible to obtain a better control of the bottom block filing, and especially to control when the metal overhangs the peripheral ledge during casting.

[0034] Advantageously an internal top edge of the enlarged portion presents a curvature radius comprised between 4 mm an 6 mm, and typically sensibly equal to 5 mm. Thus, it is possible to avoid late filling of metal at the level of the enlarged portion.

[0035] According to one embodiment, the enlarged portion is beveled at least partially. In an embodiment the enlarged portion is beveled such that the surface of the enlarged portion is angled from a horizontal surface downward toward the central zone, the angle being typically from 1 ° to 15° and preferentially about 3°.

[0036] According to one embodiment, the main surface comprises a central zone disposed in the center of the main surface, and disjoint from the peripheral ledge.

[0037] Thus, it is possible to direct the flow of liquid metal at the level of said central zone when starting the casting operation.

[0038] According to one embodiment, the enlarged portion presents a length, which is strictly inferior to a length of the central zone counted parallel to the extension direction of the side wall. According to one embodiment, the main surface is formed by the central zone and the curved zone.

[0039] According to one embodiment, the central zone comprises a hollow stamp, carved into the main body, said hollow stamp being disposed inside the central zone, and centered in the central zone.

[0040] Advantageously, the hollow stamp allows designing a key lock in the ingot of metal, said key lock being adapted to maintain the ingot stable in the mold during casting.

[0041] According to one embodiment, the enlarged portion length is strictly superior to an hollow stamp length counted parallel to the extension direction of the side wall.

[0042] According to one embodiment, the hollow stamp presents a hollow stamp length comprised from 200 mm to 500 mm and typically sensibly equal to 350 mm or 250 mm.

[0043] If the hollow stamp length is at least 250 mm, a ratio of the longitudinal length over the enlarged portion length is at least 1 .3. Thus it is possible to limit the constraint formation in the bottom block.

[0044] According to one embodiment, the central zone is flat.

[0045] Thus, the main surface and the central zone are adapted to direct the flow of liquid metal first at the level of the central zone, and then radially towards the peripheral ledge. As a result, the flow of liquid metal at the beginning of the casting in better controlled.

[0046] According to one embodiment, the border zone forms a border angle with a plane parallel to a plane formed by the flat central zone. For example, the border angle is comprised from 40° to 60° and preferentially sensibly equal to 45°.

[0047] According to one embodiment, the enlarged portion is connected to the rest of the at least one side wall by a junction portion, said junction portion presenting a junction width which decrease between the enlarged width and the largest width of the rest of said at least one side wall.

[0048] According to one embodiment, the junction width decreases linearly at an angle comprised from 15° to 40°, preferably from 20° to 35°, and typically sensibly equal to 30°.

[0049] According to one embodiment, the closed edge comprises an internal ridge facing the main surface, said internal ridge being sharp excepted at the level of the enlarged portion where the internal ridge presents a radius of curvature comprised from 1 to 15 mm, preferably from 2 to 10 mm and preferentially sensibly equal to 3 mm.

[0050] Thus, it is possible to delay the liquid metal overflow at the level of the sharp ridge, and to allow easy and quick liquid metal overflow at the level of the enlarged portion. Consequently, the liquid metal will reach the external side of the peripheral ledge approximately at the same time.

[0051] By “sharp” we mean that there is an angle discontinuity at the level of the sharp ridge.

[0052] The object of the invention may also be achieved by implementing a system for casting metal comprising: a casting mold comprising a mold cavity, said mold cavity defining an upwardly open inlet for the supply of metal and a downwardly facing outlet; a bottom block as described above, disposed at the level of the outlet of the casting mold; a movable support configured to move the bottom block along the casting direction; cooling means configured to cool the metal during casting.

[0053] The provisions previously described allows to propose a system for casting metal showing extended lifetime.

[0054] The object of the invention may also be achieved by implementing a system for semi-continuous casting metal ingots comprising: a casting frame delimiting a casting enclosure; said casting frame comprising internally a water chamber configured to receive water for cooling the metal during casting, and forming a solid metal ingot; a molten metal supply for continuously supplying molten metal to the casting enclosure at a first end; a bottom block as described above, disposed at the level of a second end, opposite to the first end along the casting direction; a movable support configured to move the bottom block along the casting direction; an alternating current source; an electromagnetic inductor positioned adjacent said casting enclosure, said electromagnetic inductor being energized by the alternating current source for producing an electromagnetic field; a metallic shield surrounding said casting enclosure at a location intermediate between said metal ingot being formed and the electromagnetic inductor for blocking out virtually all of said electromagnetic field above a lower end of said metallic shield, and allowing said electromagnetic field to exist at the level of the metal ingot being formed immediately below the casting enclosure.

[0055] Thus, it is possible to perform electromagnetic casting. Said casting technique has the advantage of limiting the need for scalping the ingot after casting.

[0056] Advantageously, the hydrostatic pressure induced by the metallic shield helps to generate an equilibrium with the magnetic pressure induced by the inductor. As a result, the shape of the meniscus at the surface of the metal ingot is better controlled.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The foregoing and other purposes, features, aspects and advantages of the invention will become apparent from the following detailed description of embodiments, given by way of illustration and not limitation with reference to the accompanying drawings, in which the same reference refer to similar elements or to elements having similar functions, and in which:

[0059] Figure 1 represents a perspective view of a bottom block according to a particular embodiment of the invention.

[0060] Figure 2 represents a top view of the bottom block of figure 1 .

[0061] Figure 3 represents a cross sectional view of the bottom block of figure 1 .

[0062] Figure 4 represents a cross sectional view of the bottom block of figure 1 .

[0063] Figure 5 represents an electromagnetic continuous metal casting system adapted to work with the bottom block of figure 1 .

[0064] DETAILED DESCRIPTION

[0065] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the various elements are not represented to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with one another.

[0066] As illustrated on figures 1 to 4, the invention concerns a bottom block 10 for a semi-continuous metal casting mold system 1 . Generally, and as represented on figures 2, the metal is casted along a casting direction called “Z”, that may be a sensibly vertical direction.

[0067] The bottom block 10 comprises a main body 30 comprising a main surface 31 adapted to receive the metal to be casted, and a peripheral ledge 50 defining a closed edge encircling the main surface 31 .

[0068] The peripheral ledge 50 is protruding from the main surface 31 along the casting direction Z, and comprises side walls 51 . The non-limiting embodiment represented on figure 1 to 4 represents a peripheral ledge 50 comprising a pair of facing longitudinal side walls 51 and a pair of lateral side walls 51 defining a quadrilateral closed edge of the peripheral ledge 50. The longitudinal side walls 51 extends along a longitudinal direction called “X”, and the lateral side walls 51 extends along a lateral direction called “Y”. The casting direction Z, the longitudinal direction X and the lateral direction Y may be perpendicular to each other. More particularly, the closed edge of the peripheral ledge 50 may be sensibly rectangular. Thus, it is possible to cast ingots having a generally rectangular cross-section. It should be noted that a direct chill casting mold to produce an ingot with a generally rectangular profile does not have a perfectly rectangular mold cavity due to the deformation of the ingot as it cools after leaving the mold cavity. It should further be appreciated that by generally rectangular or rectangular it is included shapes having substantially linear sides which may include several segments, arcuate, convex and concave and rounded angles. However, such shape is not mandatory, and the closed edge of the peripheral ledge 50 may presents any other shape such as a circular shape, or equivalent.

[0069] At least one side wall 51 comprises an enlarged portion 53, which presents an enlarged width w53 counted perpendicular to the casting direction Z which is strictly superior to a largest width w51 of the rest of said at least one side wall 51 . Generally, the enlarged width w53 is counted along the lateral direction Y.

[0070] When the peripheral ledge 50 comprises a pair of facing longitudinal side walls 51 and a pair of lateral side walls 51 , each longitudinal side wall 51 may comprise an enlarged portion 53 presenting an enlarged width w53 counted perpendicular to the casting direction Z which is strictly superior to a largest width w51 of the rest of said longitudinal side wall 51. Thus, it is possible to reinforce mechanically the longitudinal side walls 51 which are usually more constraint by the liquid metal than the lateral side walls 51 .

[0071] Generally, the enlarged width w53 is superior to 10 mm, and may be inferior to 70 mm, more particularly to 60 mm and preferably inferior to 50 mm. Notably, the enlarged width w53 can be comprised from 25 mm to 51 mm, and notably sensibly equal to 42 mm. According to one embodiment, a ratio of the enlarged width w53 over the largest width w51 of the rest of said at least one side wall is at least 1.1 , 1 .5, 2.0, 2.5, or 3.0.

[0072] Each longitudinal side wall 51 may present a longitudinal length L counted along the longitudinal direction X, and each enlarged portion 53 presents an enlarged portion length L1 counted along the longitudinal direction X. Advantageously, a ratio of the longitudinal length L over the enlarged portion length L1 is comprised from 1.5 to 6.0, preferentially from 2.0 to 5.5, and more preferentially from 2.5 to 5.0. This arrangement is a good compromise to reduce damages on the bottom block along with allowing good casting. Besides, the enlarged portion length L1 can be comprised from 35 cm to 60 cm and preferentially typically equal to about 45cm.

[0073] As illustrated on figure 1 and 2, it is possible that the enlarged portion 53 includes a center of the at least one side wall 51 . More particularly, the enlarged portion 53 may present a symmetrical shape compared to the center of the side wall 51 in which said enlarged portion 53 is included. Thus, it is possible to avoid any dissymmetrical shape in the final ingot. For example, the enlarged portion 53 presents a general rectangular shape centered in the middle of the length of the side wall 51 .

[0074] Advantageously, the enlarged portion 53 is connected to the rest of the at least one side wall 51 by a junction portion 55 which presents a junction width which decrease between the enlarged width w53 and the largest width w51 of the rest of said at least one side wall 51. Generally, the junction portion 55 is included to the enlarged portion 53. Notably, the junction width decreases linearly at an angle comprised from 15° to 40°, preferably from 20° to 35°, and typically sensibly equal to 30°. Said angle allows to avoid shrinkage constrain during curling. In other words, the junction width forms a ramp which decreases between the enlarged width w53 and the largest width w51 of the rest of said at least one side wall 51.

[0075] According to one variant, the closed edge comprises an internal ridge 54 facing the main surface 31 , said internal ridge 54 being sharp excepted at the level of the enlarged portion 53 where the internal ridge 54 presents a radius of curvature r54 comprised from 1 to 15 mm, and preferentially sensibly equal to 3 mm. By “sharp” we mean that there is an angle discontinuity at the level of the sharp ridge. Thus, it is possible to delay the liquid metal overflow at the level of the sharp ridge, and to allow easy and quick liquid metal overflow at the level of the enlarged portion 53. Consequently, the liquid metal will reach the whole external side of the peripheral ledge 50 approximately at the same time. In other words, the enlarged portion 53 is beveled at least partially.

[0076] Figures 1 to 4 described a non-limiting variant where the main surface 31 is shared in several zones. First, the main surface 31 can comprise a curved zone 33. A curvature of said curved zone 33 can be convergent towards the peripheral ledge 50. Thus, when the bottom block 10 is filed with molten metal, the filling of the bottom block 10 is realized from the center of the main surface 31 , and towards the peripheral ledge 50. The curved zone 33 may comprise a border zone 35 defined adjacent to the enlarged portion 53, said border zone 35 presenting a radius of curvature r35 which is strictly inferior to a lowest radius of curvature r33 of the rest of the curved zone 33. Thus, it is possible to obtain a better control of the bottom block 10 filing, and especially to control when the metal overhangs the peripheral ledge 50 during casting.

[0077] The main surface 31 can also comprise a central zone 37 disposed in the center of the main surface 31 , and disjoint from the peripheral ledge 50. . Thus, it is possible to direct the flow of liquid metal at the level of said central zone 37 when starting the casting. The central zone 37 can be adjacent to the curved zone 33, so that the main surface 31 is formed by the central zone 37 and the curved zone 33. For example, the central zone 37 is flat. Thus, the main surface 31 and more particularly the central zone 37, are adapted to direct the flow of liquid metal first at the level of the central zone 37, and then radially towards the peripheral ledge 50. As a result, the flow of liquid metal at the beginning of the casting is better controlled. According to one embodiment, the border zone 53 forms a border angle a53 with a plane parallel to a plane formed by the flat central zone 37. For example, the border angle a53 is comprised from 40° to 60° and preferentially sensibly equal to 45°.

[0078] Advantageously, the enlarged portion length L1 is at most equal and preferably strictly inferior to a length of the central zone 37 counted parallel to the extension direction of the side wall 51 .

[0079] The central zone 37 can comprises a hollow stamp 39, carved into the main body 30, said hollow stamp 39 being disposed inside the central zone 37, and centered in the central zone 37. Advantageously, the hollow stamp 39 allows designing a key lock in the ingot of metal, said key lock being adapted to maintain the ingot stable in the mold during casting.

[0080] Advantageously, the enlarged portion length L1 is strictly superior to a hollow stamp length L2 counted parallel to the extension direction of the side wall 51 . For example, the hollow stamp 39 presents a hollow stamp length L2 comprised from 200 mm to 500 mm, and typically sensibly equal to 350 mm or 250 mm. If the hollow stamp length L2 is equal to 250 mm, a ratio of the longitudinal length L over the enlarged portion length L1 may be superior to 1 .3. Thus it is possible to limit the constraint formation in the bottom block 10.

[0081] Finally, the central zone 37 may comprise apertures 32 configured to allow expelling excess of heat during casting. The provisions previously described allows designing a bottom block 10 for a semi-continuous casting mold system 1 with a peripheral ledge 50 presenting an improved mechanical resistance.

[0082] The invention also concerns a system 1 for casting metal comprising: a casting mold comprising a mold cavity, said mold cavity defining an upwardly open inlet for the supply of metal and a downwardly facing outlet; a bottom block 10, disposed at the level of the outlet of the casting mold; a movable support configured to move the bottom block 10 along the casting direction Z; cooling means configured to cool the metal during casting.

[0083] The provisions previously described allows to propose a system 1 for casting metal showing extended lifetime.

[0084] Finally, and as illustrated on figure 5, the invention concerns a system 1 for semi-continuous casting metal ingots Ml comprising: a casting frame 2 delimiting a casting enclosure 3; said casting frame 2 comprising internally a water chamber 4 configured to receive water for cooling the metal during casting, and forming a solid metal ingot Ml; a molten metal supply for continuously supplying molten metal to the casting enclosure 3 at a first end; a bottom block 10, disposed at the level of a second end, opposite to the first end along the casting direction Z; a movable support configured to move the bottom block 10 along the casting direction Z; an alternating current source; an electromagnetic inductor 5 positioned adjacent said casting enclosure 3, said electromagnetic inductor 5 being energized by the alternating current source for producing an electromagnetic field; a metallic shield 7 surrounding said casting enclosure 3 at a location intermediate between said metal ingot Ml being formed and the electromagnetic inductor 5 for blocking out virtually all of said electromagnetic field above a lower end of said metallic shield 7, and allowing said electromagnetic field to exist at the level of the metal ingot Ml being formed immediately below the casting enclosure 3.

[0085] Thus, it is possible to perform electromagnetic casting. Said casting technique has the advantage of limiting the need for scalping the ingot after casting.

[0086] Advantageously, the hydrostatic pressure induced by the metallic shield 7 helps to generate an equilibrium with the magnetic pressure induced by the inductor. As a result, the shape of the meniscus at the surface of the metal ingot Ml is better controlled.

Claims

CLAIMS1 . Bottom block (10) for a semi-continuous metal casting mold system (1) comprising:- a main body (30) comprising a main surface (31) adapted to receive the metal to be casted;- a peripheral ledge (50) defining a closed edge encircling the main surface (31), and protruding from the main surface (31) along a casting direction (Z), the peripheral ledge (50) comprising side walls (51); at least one side wall (51) comprising an enlarged portion (53), said enlarged portion (53) presenting an enlarged width (w53) counted perpendicular to the casting direction (Z) which is strictly superior to a largest width (w51) of the rest of said at least one side wall (51).

2. Bottom block (10) according to claim 1 , wherein the at least one side wall (51) comprises a pair of facing longitudinal side walls (51) and a pair of lateral side walls (51) defining a quadrilateral closed edge of the peripheral ledge (50), each longitudinal side wall (51) comprising an enlarged portion (53) presenting an enlarged width (w53) counted perpendicular to the casting direction (Z) which is strictly superior to a largest width (w51) of the rest of said longitudinal side wall (51).

3. Bottom block (10) according to claim 2, wherein the closed edge of the peripheral ledge (50) is sensibly rectangular.

4. Bottom block (10) according to any one of claims 2 or 3, wherein the enlarged portion (53) includes a center of the at least one side wall (51).

5. Bottom block (10) according claim 4, wherein the enlarged portion (53) presents a symmetrical shape compared to the center of the side wall (51) in which said enlarged portion (53) is included6. Bottom block (10) according to anyone of claims 2 to 5, wherein each longitudinal side wall (51) presents a longitudinal length (L) counted along a longitudinal direction (X) perpendicular to the casting direction (Z) and to the enlarged width (w53), and wherein each enlarged portion (53) presents an enlarged portion length (L1) counted along the longitudinal direction (X); a ratio of the longitudinal length (L) over the enlarged portion length (L1) being comprised from 1 to 1.5, preferentially from 1.2 to 1.4, and preferentially sensibly equal to 1.3.

7. Bottom block (10) according to any one of claims 1 to 6, wherein the main surface (31) comprises a curved zone (33), a curvature of said curved zone (33) being convergent towards the peripheral ledge (50).

8. Bottom block (10) according to claim 7, wherein the curved zone (33) comprises a border zone (35) defined adjacent to the enlarged portion (53), said border zone (35) presenting an angle of curvature which is strictly superior to a largest angle of curvature of the rest of the curved zone (33).

9. Bottom block (10) according to any one of claims 1 to 8, wherein the main surface (31) comprises a central zone (37) disposed in the center of the main surface (31), and disjoint from the peripheral ledge (50).

10. Bottom block (10) according to claim 9, wherein the central zone (37) comprises a hollow stamp (39), carved into the main body (30), said hollow stamp (39) being disposed inside the central zone (37), and centered in the central zone (37).

11. Bottom block (10) according to any one of claims 9 or 10, wherein the central zone (37) is flat.

12. Bottom block (10) according to any one of claims 1 to 11 , wherein the enlarged portion (53) is connected to the rest of the at least one side wall (51) by a junction portion (55), said junction portion (55) presenting a junction width which decrease between the enlarged width (w53) and the largest width (w51) of the rest of said at least one side wall (51).

13. Bottom block (10) according to any one of claims 1 to 12, wherein the closed edge comprises an internal ridge (54) facing the main surface (31), said internal ridge (54) being sharp excepted at the level of the enlarged portion (53) where the internal ridge (54) presents a radius of curvature (r54) comprised from 1 to 15 mm, and preferentially sensibly equal to 3 mm.

14. System (1) for casting metal comprising:- a casting mold comprising a mold cavity, said mold cavity defining an upwardly open inlet for the supply of metal and a downwardly facing outlet;- a bottom block (10) according to any one of claims 1 to 13, disposed at the level of the outlet of the casting mold;- a movable support configured to move the bottom block (10) along the casting direction (Z);- cooling means configured to cool the metal during casting.

15. System (1) for semi-continuous casting metal ingots (Ml) comprising:- a casting frame (2) delimiting a casting enclosure (3); said casting frame (2) comprising internally a water chamber (4) configured to receive water for cooling the metal during casting, and forming a solid metal ingot (Ml);- a molten metal supply for continuously supplying molten metal to the casting enclosure (3) at a first end;- a bottom block (10) according to any one of claims 1 to 13, disposed at the level of a second end, opposite to the first end along the casting direction (Z); a movable support configured to move the bottom block (10) along the casting direction (Z);- an alternating current source; an electromagnetic inductor (5) positioned adjacent said casting enclosure (3), said electromagnetic inductor (5) being energized by the alternating current source for producing an electromagnetic field; - a metallic shield (7) surrounding said casting enclosure (3) at a location intermediate between said metal ingot (Ml) being formed and the electromagnetic inductor (5) for blocking out virtually all of said electromagnetic field above a lower end of said metallic shield (7), and allowing said electromagnetic field to exist at the level of the metal ingot (Ml) being formed immediately below the casting enclosure (3).

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