Patent Publication Number: US-11027331-B2

Title: Molding facility

Description:
FIELD 
     The present invention relates to a molding facility provided with a mold used in continuous casting and an electromagnetic force generating device imparting electromagnetic force to molten metal in that mold. 
     BACKGROUND 
     In continuous casting, molten metal stored once in a tundish (for example, molten steel) is poured through a submerged nozzle into a mold from above. There, the outer circumferential surface is cooled and the solidified cast slab is pulled out from the bottom end of the mold whereby the metal is continuously cast. In the cast slab, the solidified part at the outer circumferential surface is called the “solidified shell”. 
     Here, the molten metal contains bubbles of inert gas (for example, Ar gas) supplied together with the molten metal so as to prevent clogging of the discharge holes of the submerged nozzle, contains nonmetallic inclusions, etc. If these impurities remain in the cast slab after casting, they will cause the quality of the finished product to deteriorate. In general, the specific gravity of these impurities is smaller than that of the molten metal. Thus, they are often removed upon floating up in the molten metal during continuous casting. Therefore, if making the casting speed increase, these impurities no longer sufficiently float up and are separated and the quality of the cast slab tends to fall. In this way, in continuous casting, there is a tradeoff between the productivity and the quality of the cast slab, that is, in this relation, if pursuing productivity, the quality of the cast slab deteriorates while if giving priority to the quality of the cast slab, the productivity falls. 
     In recent years, the quality sought for some products such as external panels for automobiles has been becoming increasingly tough. Therefore, in continuous casting, to achieve quality, productivity has tended to be sacrificed in operations. In view of such a situation, in continuous casting, art for securing the quality of the cast slab while further improving productivity has been sought. 
     On the other hand, it is known that the quality of the cast slab is greatly affected by the flow motion of the molten metal in the mold at the time of continuous casting. Therefore, it is possible that by suitably controlling the flow motion of the molten metal in the mold, the desired quality of the cast slab can be maintained while realizing high speed, stable operation, that is, improving the productivity. 
     To control the flow motion of the molten metal in the mold, art is being developed for use of an electromagnetic force generating device imparting electromagnetic force to the molten metal in the mold. Note that, in this Description, the group of members around a mold, including the mold and electromagnetic force generating device, will be referred to for convenience as a “molding facility”. 
     Specifically, as an electromagnetic force generating device, an electromagnetic brake device and electromagnetic stirring device are being widely used. Here, an “electromagnetic brake device” is a device applying a stationary magnetic field to the molten metal to thereby cause the generation of a braking force inside the molten metal and suppress flow motion of the molten metal. On the other hand, an “electromagnetic stirring device” is an device applying a moving magnetic field to molten metal to thereby cause the generation of an electromagnetic force called a “Lorentz force” in the molten metal and impart to the molten metal a pattern of flow motion making it swirl in the horizontal plane of the mold. 
     An electromagnetic brake device is generally provided so as to cause the generation in the molten metal of a braking force weakening the strength of the discharge flow ejected from the submerged nozzle. Here, the discharge flow from the submerged nozzle strikes the inside walls of the mold to thereby form an ascending flow heading in the upper direction (that is, direction where surface of molten metal is present) and a descending flow heading in the lower direction (that is, direction in which the cast slab is pulled out). Therefore, by the strength of the discharge flow being weakened by the electromagnetic brake device, the strength of the ascending flow is weakened and the fluctuation of the melt surface of the molten metal can be suppressed. Further, the strength of the discharge flow striking the solidified shell is also weakened, so the effect of suppressing breakout due to remelting of the solidified shell can be obtained. In this way, an electromagnetic brake device is used in the case of aiming at high speed, stable casting. Further, due to the electromagnetic brake device, the flow rate of the descending flow formed by the discharge flow is suppressed, so floating and separation of impurities in the molten metal are promoted and the effect of improving the internal quality of the cast slab (below, also referred to as the “inside quality”) can also be obtained. 
     On the other hand, as a shortcoming of an electromagnetic brake device, mention may be made of the fact that the flow rate of molten metal at the interface with the solidified shell becomes lower, so sometimes the surface quality deteriorates. Further, it becomes harder for the ascending flow formed by the discharge flow to reach the melt surface, so due to the drop in melt surface temperature, skinning occurs and flaws are liable to be caused in the inside quality. 
     An electromagnetic stirring device, as explained above, imparts a predetermined pattern of flow motion to the molten metal, that is, causes generation of a stirring flow inside the molten metal. Due to this, flow motion of the molten metal at the interface with the solidified shell is promoted, so the above-mentioned Ar gas bubbles or nonmetallic inclusions or other impurities are kept from being trapped inside the solidified shell and the surface quality of the cast slab can be improved. On the other hand, as a shortcoming of an electromagnetic stirring device, due to the stirring flow striking the inside wall of the mold, in the same way as the discharge flow from the above-mentioned submerged nozzle, an ascending flow and a descending flow are generated, so sometimes the inside quality of the cast slab will be lowered by the ascending flow capturing powder at the melt surface and the descending flow carrying impurities downward at the mold. 
     As explained above, an electromagnetic brake device and electromagnetic stirring device have respective good points and bad points from the viewpoint of securing the quality of the cast slab. Therefore, for the purpose of improving both the surface quality and inside quality of the cast slab, art is being developed for continuous casting using a molding facility provided with both an electromagnetic brake device and electromagnetic stirring device at the mold or a molding facility provided with a plurality of electromagnetic stirring devices at the mold. 
     For example, PTL 1 discloses a molding facility provided with an electromagnetic stirring device above the mold (more particularly, near the meniscus) and provided with an electromagnetic brake device below the mold. PTL 1 describes that, due to this constitution, the effect is obtained that the surface quality of the cast slab can be improved by the electromagnetic stirring device and entrance of inclusions into the cast slab which can remarkably occur when performing high speed casting can be reduced by the electromagnetic brake device (that is, the inside quality can be improved). Further, for example, PTL 2 discloses a molding facility provided with two stages of electromagnetic stirring devices in the vertical direction. PTL 2 describes that by such a constitution, the effect can be obtained that the surface quality of the cast slab can be improved by the top stage electromagnetic stirring device causing electromagnetic force to act on the molten metal near the meniscus and that the inside quality of the cast slab can be improved by the bottom stage electromagnetic stirring device causing electromagnetic force to act on the discharge flow from the submerged nozzle. 
     Further, PTL 3 describes a continuous casting device with an electromagnetic stirring device EMS placed above the mold and with an electromagnetic brake device LMF placed so that the top end of the core becomes a position of a predetermined distance from the top part of the mold. Further, PTL 4 relates to a continuous casting method for steel and describes a configuration using an electromagnetic stirring coil and electromagnetic brake device. 
     CITATIONS LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Publication No. 6-226409 
     [PTL 2] Japanese Unexamined Patent Publication No. 2000-61599 
     [PTL 3] Japanese Unexamined Patent Publication No. 2015-27687 
     [PTL 4] Japanese Unexamined Patent Publication No. 2002-45953 
     SUMMARY 
     Technical Problem 
     However, in the molding facility disclosed in PTL 1, the bottom end of the electromagnetic brake device is positioned below the mold. The electromagnetic force (braking force) generated by the electromagnetic brake acts in accordance with the flow rate of the molten metal, so with such a set position, it is feared that the electromagnetic force acting on the molten metal will become extremely small compared with the case of setting the electromagnetic brake device near the discharge holes of the submerged nozzle. That is, the effect of improvement of the inside quality of the cast slab by the electromagnetic brake device at the time of high speed casting described in PTL 1 may be limited. Regarding this point, the inventors ran simulations by numerical analysis for study assuming general casting conditions (size of cast slab and type of product, position of submerged nozzle, etc.) As a result, they newly learned that in the case of setting the electromagnetic brake device at the position described in PTL 1, if making the casting speed increase to improve the productivity, the problem may arise that to be able to suitably prevent entry of inclusions, the casting speed must be no more than 1.6 m/min or so and that if the casting speed exceeds 1.6 m/min or so, it is difficult to effectively prevent the entry of inclusions. 
     Further, in the molding facility disclosed in PTL 2, no electromagnetic brake device is used. The electromagnetic stirring device is used to create an upward force acting on the discharge flow so as to reduce the strength of the discharge flow. However, the electromagnetic force generated due to electromagnetic stirring acts without regard as to fluctuations in the flow rate of the discharge flow, so it is believed difficult to use the electromagnetic stirring device to stably control the flow rate of the discharge flow. The inventors studied this and as a result newly learned that the problem may arise that if trying to use the molding facility described in PTL 2 to control the flow motion of molten metal inside the mold, due to the above-mentioned difficulty in control of the discharge flow by the electromagnetic stirring device, the flow motion of the molten metal easily becomes unstable and the inside quality of the cast slab will easily fluctuate. 
     Further, the arts described in PTL 3 and PTL 4 all had casting speeds of low speeds of 1.5 m/min or less and did not envision high speed casting. 
     There is still room for study regarding the suitable configuration of an electromagnetic force generating device able to achieve the quality of the cast slab while improving the productivity. Therefore, the present invention was made in consideration of the above problem. The present invention has as its object the provision of a new and improved molding facility able to stably achieve the quality of the cast slab even in a case of improving the productivity in continuous casting. 
     Solution to Problem 
     The inventors tried using a molding facility combining an electromagnetic brake device and an electromagnetic stirring device in continuous casting to stabilize the flow motion of molten metal inside the mold so as to achieve the quality of the cast slab while improving the productivity. However, these devices were not ones where the good points of the two devices could be simply obtained by just installing the two devices. For example, as will be understood from the effect on the flow rate of molten metal at the interface of the solidified shell explained above, these devices have aspects acting to cancel out each other&#39;s effects. Therefore, in continuous casting using both an electromagnetic brake device and electromagnetic stirring device, quite often the quality of the cast slab (surface quality and inside quality) will end up deteriorating compared with the case of using these devices respectively alone. 
     Therefore, the inventors ran repeated simulations by numerical analysis and actual machine tests and engaged in in-depth studies. As a result, they discovered that in continuous casting using an electromagnetic brake device and electromagnetic stirring device, to more effectively draw out the effect of improvement of the quality of the cast slab and enable the quality of the cast slab to be achieved even when improving the productivity, it is important to suitable define the configurations and positions of placement of these devices. 
     That is, to solve the above technical problem, according to one aspect of the present invention, there is provided a molding facility comprising a mold for continuous casting use, a first water box and second water box storing cooling water for cooling the mold, an electromagnetic stirring device imparting to molten metal in the mold an electromagnetic force causing a swirling flow to be generated in a horizontal plane, and an electromagnetic brake device imparting an electromagnetic force to a discharge flow of molten metal to an inside of the mold from a submerged nozzle in a direction braking the discharge flow, the first water box, the electromagnetic stirring device, the electromagnetic brake device, and the second water box being placed in that order from above to below at an outside surface of a long side mold plate of the mold, a core height H 1  of the electromagnetic stirring device and a core height H 2  of the electromagnetic brake device satisfying a relationship shown in the following numerical formula (101): Here, the casting speed may be 2.0 m/min or less. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
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                   0.80 
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                   ≤ 
                   2.33 
                 
               
               
                 
                   ( 
                   101 
                   ) 
                 
               
             
           
         
       
     
     Further, in the molding facility, the core height H 1  of the electromagnetic stirring device and the core height H 2  of the electromagnetic brake device may satisfy the relationship shown in the following numerical formula (103): Here, the casting speed may be 2.2 m/min or less. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
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                     2 
                   
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                   ( 
                   103 
                   ) 
                 
               
             
           
         
       
     
     Further, the core height H 1  of the electromagnetic stirring device and the core height H 2  of the electromagnetic brake device may satisfy the relationship shown in the following numerical formula (105): Here, the casting speed may be 2.4 m/min or less. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
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                   ( 
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     Further, the core height H 1  of the electromagnetic stirring device and the core height H 2  of the electromagnetic brake device may satisfy the relationship shown in the following numerical formula (2):
 
[Mathematical 4]
 
 H 1+ H 2≤500 mm  (2)
 
     Further, the electromagnetic brake device may be comprised of a split brake. 
     Advantageous Effects of Invention 
     As explained above, according to the present invention, it becomes possible to achieve the quality of the cast slab in continuous casting even if improving the productivity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side cross-sectional view schematically showing one example of the configuration of a continuous casting machine according to the present embodiment. 
         FIG. 2  is a cross-sectional view along a Y-Z plane of a molding facility according to the present embodiment. 
         FIG. 3  is a cross-sectional view of a molding facility at an A-A cross-section shown in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of a molding facility at a B-B cross-section shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a molding facility at a C-C cross-section shown in  FIG. 3 . 
         FIG. 6  is a view for explaining the direction of the electromagnetic force imparted by the electromagnetic brake device to the molten steel. 
         FIG. 7  is a view showing the relationship between the casting speed (m/min) and the distance from the surface of the molten steel (mm) when the thickness of the solidified shell becomes 4 mm or 5 mm. 
         FIG. 8  is a graph showing the relationship between a core height ratio H 1 /H 2  and a pinhole index in the case where the casting speed is 1.4 m/min obtained by simulation by numerical analysis. 
         FIG. 9  is a graph showing the relationship between the core height ratio H 1 /H 2  and the pinhole index in the case where the casting speed is 2.0 m/min obtained by simulation by numerical analysis. 
         FIG. 10  is a graph showing the relationship between the casting speed and inside quality obtained by simulation by numerical analysis. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, while referring to the attached drawings, preferred embodiments of the present invention will be explained in detail. Note that, in the Description and drawings, component elements having substantially the same functions and configurations will be assigned the same reference notations and overlapping explanations will be omitted. 
     Note that, in the drawings shown in the Description, for explanation, sometimes some of the component elements will be represented exaggerated in size. The relative sizes of the members illustrated in the drawings do not necessarily accurately represent the relative sizes of the actual members. 
     Further, below, as one example, embodiments where the molten metal is molten steel will be explained. However, the present invention is not limited to such examples. The present invention may be applied to continuous casting of other metals as well. 
     1. Configuration of Continuous Casting Machine 
     Referring to  FIG. 1 , the configuration of a continuous casting machine according to one preferred embodiment of the present invention and a continuous casting method will be explained.  FIG. 1  is a side cross-sectional view schematically showing one example of the constitution of the continuous casting machine according to the present embodiment. 
     As shown in  FIG. 1 , the continuous casting machine  1  according to the present embodiment is an apparatus using a mold  110  for continuous casting use to continuously cast molten steel  2  and produce a steel slab or other cast slab  3 . The continuous casting machine  1  is provided with a mold  110 , a ladle  4 , a tundish  5 , a, submerged nozzle  6 , a secondary cooling device  7 , and a cast slab cutter  8 . 
     The ladle  4  is a movable vessel for conveying molten steel  2  from the outside to the tundish  5 . The ladle  4  is arranged above the tundish  5 . Molten steel  2  inside the ladle  4  is supplied to the tundish  5 . The tundish  5  is arranged above the mold  110 , stores molten steel  2 , and removes inclusions in the molten steel  2 . The submerged nozzle  6  extends from the bottom end of the tundish  5  downward toward the mold  110 . The front end of the submerged nozzle  6  is submerged in the molten steel  2  in the mold  110 . The submerged nozzle  6  continuously supplies molten steel  2  from which inclusions were removed in the tundish  5  to the inside of the mold  110 . 
     The mold  110  is a rectangular cylindrical shape designed for the width and thickness of the cast slab  3 . For example, it is assembled so that a pair of long side mold plates (corresponding to long side mold plates  111  shown in  FIG. 2  explained later) sandwich a pair of short side mold plates (corresponding to short side mold plates  112  shown in  FIG. 4  to  FIG. 6  explained later) from the two sides. The long side mold plates and short side mold plates (below, sometimes referred to all together as the “mold plates”), for example, are water-cooled copper plates at which channels are provided for flow of cooling water. The mold  110  cools the molten steel  2  contacting the mold plates to produce a cast slab  3 . The cast slab  3  moves toward the bottom through the mold  110 . Along with this, the inside unsolidified part  3   b  proceeds to be solidified whereby the outside solidified shell  3   a  gradually becomes greater in thickness. The cast slab  3  including the solidified shell  3   a  and the unsolidified part  3   b  is pulled out from the bottom end of the mold  110 . 
     Note that, in the following explanation, the up-down direction (that is, the direction in which the cast slab  3  is pulled out from the mold  110 ) will also be called the “Z-axis direction”. Further, the two directions perpendicular to each other in the plane vertical to the Z-axis direction (horizontal plane) will also be called the “X-axis direction” and “Y-axis direction”. Further, the X-axis direction is defined as the direction parallel to the long sides of the mold  110  in the horizontal plane while the Y-axis direction is defined as the direction parallel to the short sides of the mold  110  in the horizontal plane. Further, in the following explanation, when expressing the sizes of the members, sometimes the length of a member in the Z-axis direction will be referred to as the “height” while the length of that member in the X-axis direction or Y-axis direction will be referred to as the “width”. 
     Here, in  FIG. 1 , while illustration is omitted for avoiding complication of the drawing, in the present embodiment, an electromagnetic force generating device is set at the outside surface of a long side mold plate of the mold  110 . The electromagnetic force generating device is provided with an electromagnetic stirring device and electromagnetic brake device. In the present embodiment, by driving the electromagnetic force generating device while performing continuous casting, it becomes possible to achieve the quality of the cast slab while performing casting by a higher speed. The configuration of the electromagnetic force generating device and the position of placement with respect to the mold  110  etc. will be explained later with reference to  FIG. 2  to  FIG. 5 . 
     The secondary cooling device  7  is provided at a secondary cooling zone  9  below the mold  110  and supports and conveys the cast slab  3  pulled out from the bottom end of the mold  110  while cooling it. This secondary cooling device  7  has a plurality of pairs of support rolls (for example, support rolls  11 , pinch rolls  12 , and segment rolls  13 ) arranged at the both sides of the cast slab  3  in the thickness direction and a plurality of spray nozzles (not shown) spraying the cast slab  3  with cooling water. 
     The support rolls provided at the secondary cooling device  7  are arranged in pairs at the both sides of the cast slab  3  in the thickness direction and function as supporting and conveying means for supporting the cast slab  3  while conveying it. By using the support rolls to support the cast slab  3  from the both sides in the thickness direction, it is possible to prevent breakout and bulging of the cast slab  3  during solidification at the secondary cooling zone  9 . 
     The support rolls comprised of the support rolls  11 , pinch rolls  12 , and segment rolls  13  form a conveyance path (pass line) of the cast slab  3  in the secondary cooling zone  9 . This pass line, as shown in  FIG. 1 , is vertical directly below the mold  110  and then bends to a curved shape and finally becomes horizontal. In the secondary cooling zone  9 , the part where the pass line is vertical will be referred to as the “vertical part  9 A”, the part where it bends will be referred to as the “curved part  9 B”, and the part where it is horizontal will be referred to as the “horizontal part  9 C”. A continuous casting machine  1  which has such a pass line is called a “vertical-curved type continuous casting machine  1 ”. Note that, the present invention is not limited to the vertical-curved type continuous casting machine  1  such as shown in  FIG. 1 . It can also be applied to a curved type or vertical type or other various types of continuous casting machines. 
     The support rolls  11  are undriven type rolls provided at the vertical part  9 A right below the mold  110  and support the cast slab  3  right after being pulled out from the mold  110 . The cast slab  3  right after being pulled out from the mold  110  is in a state with a thin solidified shell  3   a , so has to be supported at relatively short intervals (roll pitch) to prevent breakout or bulging. For this reason, as the support rolls  11 , small diameter rolls enabling reduction of the roll pitch are preferably used. In the example shown in  FIG. 1 , three pairs of support rolls  11  comprised of small diameter rolls are provided at a relatively narrow roll pitch at the both sides of the cast slab  3  at the vertical part  9 A. 
     The pinch rolls  12  are driven type rolls rotating by motors or other driving means and have the function of pulling out the cast slab  3  from the mold  110 . The pinch rolls  12  are arranged at suitable positions at the vertical part  9 A, curved part  9 B, and horizontal part  9 C respectively. The cast slab  3  is pulled out from the mold  110  by the force transmitted from the pinch rolls  12  and is conveyed along the pass line. Note that, the arrangement of the pinch rolls  12  is not limited to the example shown in  FIG. 1 . The positions of arrangement may be freely set. 
     The segment rolls  13  (also called “guide rolls”) are undriven type rolls provided at the curved part  9 B and horizontal part  9 C and support and guide the cast slab  3  along the pass line. The segment rolls  13  may be provided with respectively different roll sizes or roll pitches depending on the positions on the pass line and depending on which of the F surface (fixed surface, surface at bottom left side in  FIG. 1 ) of the cast slab  3  or L surface (loose surface, surface at top right in  FIG. 1 ) they are set at. 
     The cast slab cutter  8  is arranged at the terminal end of the horizontal part  9 C of the pass line and cuts the cast slab  3  conveyed along the pass line into predetermined lengths. The cut thick plate shaped cast slab  14  is conveyed to the facility at the next step by table rolls  15 . 
     Above, referring to  FIG. 1 , the overall configuration of the continuous casting machine  1  according to the present embodiment is explained. Note that, in the present embodiment, the above-mentioned electromagnetic force generating device is set at the mold  110 . That electromagnetic force generating device may be used to perform the continuous casting. The configuration at the continuous casting machine  1  other than the electromagnetic force generating device may be similar to that of a general conventional continuous casting machine. Therefore, the configuration of the continuous casting machine  1  is not limited to the one illustrated. As the continuous casting machine  1 , ones of all sorts of configuration may be used. 
     2. Electromagnetic Force Generating Device 
     2-1. Configuration of Electromagnetic Force Generating Device 
     Referring to  FIG. 2  to  FIG. 5 , the configuration of an electromagnetic force generating device provided at the above-mentioned mold  110  will be explained in detail.  FIG. 2  to  FIG. 5  are views showing one example of the configuration of the molding facility according to the present embodiment. 
       FIG. 2  is a cross-sectional view of the molding facility  10  according to the present embodiment in the Y-Z plane.  FIG. 3  is a cross-sectional view of the molding facility  10  at the A-A cross-section shown in  FIG. 2 .  FIG. 4  is a cross-sectional view of the molding facility  10  at the B-B cross-section shown in  FIG. 3   FIG. 5  is a cross-sectional view of the molding facility  10  at the C-C cross-section shown in  FIG. 3 . Note that, the molding facility  10  has a symmetric configuration about the center of the mold  110  in the Y-axis direction, so in  FIG. 2 ,  FIG. 4 , and  FIG. 5 , only the portions corresponding to one long side mold plate  111  are illustrated. Further, in  FIG. 2 ,  FIG. 4 , and  FIG. 5 , to facilitate understanding, the molten steel  2  inside the mold  110  is also illustrated. 
     Referring to  FIG. 2  to  FIG. 5 , the molding facility  10  according to the present embodiment is configured with two water boxes  130 ,  140  and an electromagnetic force generating device  170  set at the outside surface of a long side mold plate  111  of the mold  110  through the backup plates  121 . 
     The mold  110 , as explained above, is assembled so that a pair of long side mold plates  111  sandwich a pair of short side mold plates  112  from the both sides. The mold plates  111 ,  112  are made of copper plates. However, the present embodiment is not limited to such an example. The mold plates  111 ,  112  may be formed by various types of materials generally used as molds of continuous casting machines. 
     The present embodiment covers continuous casting of slabs of ferrous metals. The cast slab size is a width of (that is, length in X-axis direction) of 800 to 2300 mm or so and a thickness (that is, length in Y-axis direction) of 200 to 300 mm or so. That is, the mold plates  111 ,  112  also have sizes corresponding to the cast slab size. That is, the long side mold plates  111  have widths in the X-axis direction at least longer than the widths of 800 to 2300 mm of the cast slab  3  while the short side mold plates  112  have widths in the Y-axis direction substantially the same as the thickness of 200 to 300 mm of the cast slab  3 . 
     Further, while explained in detail later, in the present embodiment, to more effectively obtain the effect of improvement of the quality of the cast slab  3  by the electromagnetic force generating device  170 , the mold  110  is configured to be as long as possible in length in the Z-axis direction. In general, it is known that as the molten steel  2  increasingly solidifies inside the mold  110 , due to shrinkage upon solidification, the cast slab  3  ends up separating from the inside walls of the mold  110  and sometimes the cast slab  3  is not sufficiently cooled. Therefore, the length of the mold  110  is made at the longest 1000 mm or so from the surface of the molten steel as a limit. In the present embodiment, considering such a situation, the mold plates  111 ,  112  are formed so as to have lengths in the Z-axis direction sufficiently larger than the 1000 mm so that the lengths from the surface of the molten steel to the bottom ends of the mold plates  111 ,  112  become 1000 mm or so. 
     The backup plates  121 ,  122  are, for example, comprised of stainless steel. They are provided so as to cover the outside surfaces of the mold plates  111 ,  112  so as to reinforce the mold plates  111 ,  112  of the mold  110 . Below, for differentiation, the backup plates  121  provided at the outside surfaces of the long side mold plates  111  will also be referred to as the long side backup plates  121  while the backup plates  122  provided at the outside surfaces of the short side mold plates  112  will also be referred to as the short side backup plates  122 . 
     In the electromagnetic force generating device  170 , to impart electromagnetic force to the molten steel  2  in the mold  110  through the long side backup plate  121 , at least the long side backup plate  121  can be formed by a nonmagnetic material (for example, nonmagnetic stainless steel etc.) However, to achieve the high magnetic flux of the electromagnetic brake device  160  at the location of the long side backup plate  121  facing the end part  164  of the core  162  of the electromagnetic brake device  160  explained later (below, also referred to as the “electromagnetic brake core  162 ”), magnetic soft iron  124  is buried. 
     At the long side backup plate  121 , further, a pair of backup plates  123  are provided extending toward the direction (Y-axis direction) vertical to the long side backup plate  121 . As shown in  FIG. 3  to  FIG. 5 , the electromagnetic force generating device  170  is provided between this pair of backup plates  123 . In this way, the backup plates  123  can prescribe the width of the electromagnetic force generating device  170  (that is, the length in the X-axis direction) and the set position in the X-axis direction. In other words, the mounting positions of the backup plates  123  are determined so that the electromagnetic force generating device  170  can impart electromagnetic force to a desired range of the molten steel  2  in the mold  110 . Below, for differentiation, the backup plates  123  will also be referred to as “width direction backup plates  123 ”. The width direction backup plates  123  are also formed by for example stainless steel in the same way as the backup plates  121 ,  122 . 
     The water boxes  130 ,  140  store cooling water for cooling the mold  110 . In the present embodiment, as illustrated, one water box  130  is set at a region of a predetermined distance from a top end of a long side mold plate  111  while the other water box  140  is set at a region of a predetermined distance from a bottom end of the long side mold plate  111 . By providing the water boxes  130 ,  140  above and below the mold  110  in this way, it becomes possible to achieve space for setting the electromagnetic force generating device  170  between the water boxes  130 ,  140 . Below, for differentiation, the water box  130  provided above the long side mold plate  111  will also be referred to as the “upper water box  130 ” while the water box  140  provided below the long side mold plate  111  will also be referred to as the “lower water box  140 ”. 
     Inside the long side mold plates  111  or between the long side mold plates  111  and the long side backup plates  121 , channels (not shown) are formed for the cooling water to run through. These channels are extended up to the water boxes  130 ,  140 . Using a not shown pump, cooling water flows from one of the water boxes  130 ,  140  to the other of the water boxes  130 ,  140  (for example, from the lower water box  140  toward the upper water box  130 ) through the channels. Due to this, the long side mold plates  111  are cooled and molten steel  2  inside the mold  110  is cooled through the long side mold plates  111 . Note that, while illustration is omitted, the short side mold plates  112  are also provided with water boxes and water channels in the same way. Due to the flow motion of the cooling water, the short side mold plates  112  are cooled. 
     The electromagnetic force generating device  170  is provided with an electromagnetic stirring device  150  and an electromagnetic brake device  160 . As illustrated, the electromagnetic stirring device  150  and the electromagnetic brake device  160  are set in the space between the water boxes  130 ,  140 . Inside the space, the electromagnetic stirring device  150  is set above while the electromagnetic brake device  160  is set below. Note that, the heights of the electromagnetic stirring device  150  and the electromagnetic brake device  160  and the positions of setting the electromagnetic stirring device  150  and electromagnetic brake device  160  in the Z-axis direction will be explained in detail below (2-2. Details of Position of Setting Electromagnetic Force Generating Device). 
     The electromagnetic stirring device  150  applies a moving magnetic field to the molten steel  2  inside the mold  110  to thereby impart electromagnetic force to the molten steel  2 . The electromagnetic stirring device  150  is driven to apply electromagnetic force in the width direction of the long side mold plate  111  where it is set (that is, the X-axis direction) to the molten steel  2 .  FIG. 4  shows the direction of the electromagnetic force imparted to the molten steel  2  by the electromagnetic stirring device  150  in a symbolic manner by the bold arrow. Here, the electromagnetic stirring device  150  provided at the long side mold plate  111  whose illustration is omitted (that is, the long side mold plate  111  facing the illustrated long side mold plate  111 ) is driven to impart an electromagnetic force in the opposite direction to the illustration along the width direction of the long side mold plate  111  where it is set. In this way, the pair of electromagnetic stirring devices  150  are driven so as to generate a swirling flow inside the horizontal plane. According to the electromagnetic stirring devices  150 , by causing generation of such a swirling flow, the molten steel  2  at the solidified shell interface flows, a cleaning effect suppressing trapping of gas bubbles and inclusions at the solidified shell  3   a  is obtained, and the surface quality of the cast slab  3  can be improved. 
     The detailed configuration of the electromagnetic stirring device  150  will be explained. The electromagnetic stirring device  150  is comprised of a case  151 , a core  152  stored inside the case  151  (below, also referred to as an electromagnetic stirring core  152 ), and a plurality of coils  153  configured by conductors wound around the electromagnetic stirring core  152 . 
     The case  151  is a hollow member having a substantially box shape. The size of the case  151  can be suitably determined so that the electromagnetic stirring device  150  can impart electromagnetic force to a desired range of the molten steel  2 , that is, so that the coil  153  provided at the inside can be arranged at a suitable position with respect to the molten steel  2 . For example, the width W 4  of the case  151  in the X-axis direction, that is, the width W 4  of the electromagnetic stirring device  150  in the X-axis direction, is determined to become larger than the width of the cast slab  3  so as to be able to impart electromagnetic force to the molten steel  2  inside the mold  110  at any position in the X-axis direction. For example, W 4  is 1800 mm to 2500 mm or so. Further, in the electromagnetic stirring device  150 , electromagnetic force is imparted to the molten steel  2  from the coil  153  through the side walls of the case  151 , so as the material of the case  151 , for example, a nonmagnetic stainless steel or FRP (fiber reinforced plastic) or other nonmagnetic and strength-securing member is used. 
     The electromagnetic stirring core  152  is a solid member having a substantially box shape. Inside the case  151 , it is set so that its long direction becomes substantially parallel to the width direction (that is, the X-axis direction) of the long side mold plate  111 . The electromagnetic stirring core  152  is, for example, formed by stacking electromagnetic steel sheets. 
     A conductor is wound around the electromagnetic stirring core  152  centered about the X-axis direction whereby the coil  153  is formed. As such a conductor, for example, a copper one having a 10 mm×10 mm cross-section and having a diameter 5 mm or so cooling water channel inside it is used. At the time of application of current, the cooling water channel is used to cool the conductor. This conductor is insulated at its surface layer by insulating paper etc. and can be wound in layers. For example, one coil  153  is formed by winding the conductor in two to four layers. A coil  153  having a similar configuration is provided alongside it at a predetermined interval in the X-axis direction. 
     Not shown AC power supplies are connected to the respective coils  153 . Due to the AC power supplies, current is applied to the coils  153  so that the phases of the currents at the adjoining coils  153  are suitably offset, whereby electromagnetic force causing a swirling flow can be given to the molten steel  2 . Note that, the drive operation of the AC power supply can be suitably controlled by operation of a processor or other control device (not shown) in accordance with a predetermined program. Due to this control device, the amounts of current applied to the respective coils  153 , the timing of applying currents to the coils  153 , etc. are suitably controlled and the strength of the electromagnetic force given to the molten steel  2  can be controlled. As the method of driving this AC power supply, various known methods used in general electromagnetic stirring devices may be used, so here detailed explanations will be omitted. 
     The width W 1  of the electromagnetic stirring core  152  in the X-axis direction can be suitably determined so as to enable the electromagnetic stirring device  150  to impart electromagnetic force to a desired range of the molten steel  2 , that is, so that the coil  153  can be placed at a suitable position with respect to the molten steel  2 . For example, W 1  is 1800 mm or so. 
     The electromagnetic brake device  160  can apply a stationary magnetic field to the molten steel  2  in the mold  110  to thereby impart an electromagnetic force to the molten steel  2 . Here,  FIG. 6  is a view for explaining the direction of the electromagnetic force imparted by the electromagnetic brake device  160  to the molten steel  2 . In  FIG. 6 , the cross-section of the configuration near the mold  110  in the X-Z plane is schematically shown. Further, in  FIG. 6 , the electromagnetic stirring core  152  and the position of the end part  164  of the electromagnetic brake core  162  explained later are shown by a broken line in a symbolic manner. 
     As shown in  FIG. 6 , the submerged nozzle  6  can be provided with a pair of discharge holes at positions facing the short side mold plates  112 . The electromagnetic brake device  160  is driven so as to impart to the molten steel  2  an electromagnetic force in a direction restraining the flow of molten steel  2  (discharge flow) from the discharge holes of the submerged nozzle  6 .  FIG. 6  shows the direction of the discharge flow by a fine arrow in a symbolic manner and shows the direction of the electromagnetic force imparted by the electromagnetic brake device  160  to the molten steel  2  in a symbolic manner. According to the electromagnetic brake device  160 , by causing the generation of electromagnetic force in a direction restraining such a discharge flow, the effect is obtained of the descending flow being restrained and the flotation and separation of gas bubbles and inclusions being promoted and the inside quality of the cast slab  3  can be improved. 
     The detailed configuration of the electromagnetic brake device  160  will be explained. The electromagnetic brake device  160  is comprised of a case  161 , an electromagnetic brake core  162  partially stored in the case  161 , and a plurality of coils  163  comprised of conductors wound at portions of the electromagnetic brake core  162  inside the case  161 . 
     The case  161  is a hollow member having a substantially box shape. The size of the case  161  can be suitably determined so that the electromagnetic brake device  160  can impart electromagnetic force to the desired range of the molten steel  2 , that is, so that the coils  163  provided at the inside can be arranged at suitably positions with respect to the molten steel  2 . For example, the width W 4  of the case  161  in the X-axis direction, that is, the width W 4  of the electromagnetic brake device  160  in the X-axis direction, is determined to become larger than the width of the cast slab  3  so that electromagnetic force can be imparted to the molten steel  2  inside the mold  110  at a desired position of the X-axis direction. In the illustrated example, the width W 4  of the case  161  is substantially the same as the width W 4  of the case  151 . Provided, however, the present embodiment is not limited to such an example. The width of the electromagnetic stirring device  150  and the width of the electromagnetic brake device  160  may also be different. 
     Further, in the electromagnetic brake device  160 , electromagnetic force is imported to the molten steel  2  from the coil  163  through the side wall of the case  161 , so the case  161 , in the same way as the case  151 , for example, is formed by nonmagnetic stainless steel or FRP or other nonmagnetic and strength-securing material. 
     The electromagnetic brake core  162  is comprised of a pair of end parts  164  of solid members having substantially box shapes and at which coils  163  are provided and a connecting part  165  of a solid member also having substantially a box shape connecting the pair of end parts  164 . The electromagnetic brake core  162  is configured provided with a pair of end parts  164  so as to stick out from the connecting part  165  in the Y-axis direction of the direction heading toward the long side mold plate  111 . The positions at which the pair of end parts  164  are provided can be made positions at which the electromagnetic force is desired to be imparted to the molten steel  2 , that is, positions where the discharge flow from the pair of discharge holes of the submerged nozzle  6  passes through regions where a magnetic field will be applied by the coils  163  (see  FIG. 6  as well). The electromagnetic brake core  162  is, for example, formed by stacking electromagnetic steel sheets. 
     The coils  163  are formed by winding conductors around the end parts  164  of the electromagnetic brake core  162  centered about the Y-axis direction. The structures of the coils  163  are similar to the coils  153  of the electromagnetic stirring device  150 . The end parts  164  are respectively provided with pluralities of coils  163  alongside in the Y-axis direction at predetermined intervals. 
     The respective coils  163  have not shown DC power supplies connected to them. By applying DC currents to the coils  163  by the DC power supplies, electromagnetic force can be applied to the molten steel  2  weakening the strengths of the discharge flow. Note that, the drive operations of the DC power supplies can be suitably controlled by operation of a processor other control device (not shown) in accordance with a predetermined program. Due to this control device, the amounts of current supplied to the respective coils  163  etc. are suitably controlled and the strength of the electromagnetic force given to the molten steel  2  can be controlled. As the method of driving the DC power supplies, various known methods used in general electromagnetic brake devices may be used, so here detailed explanations will be omitted. 
     The width W 0  of the electromagnetic brake core  162  in the X-axis direction, the width W 2  of the end parts  164  in the X-axis direction, and the distance W 3  between the end parts  164  in the X-axis direction can be suitably determined so as to enable the electromagnetic stirring device  150  to impart electromagnetic force to a desired range of the molten steel  2 , that is, so that the coil  163  can be placed at a suitable position with respect to the molten steel  2 . For example, W 0  is 1600 mm or so, W 2  is 500 mm or so, and W 3  is 350 mm or so. 
     Here, for example, as in the art described in PTL 1, as the electromagnetic brake device, there are ones having single magnetic poles and generating a uniform magnetic field in the width direction of the mold. In an electromagnetic brake device having such a configuration, there is the defect that a uniform electromagnetic force is imparted in the width direction, so it is not possible to control in detail the range in which electromagnetic force is imparted and suitable casting conditions are limited. 
     As opposed to this, in the present embodiment, in the above way, the electromagnetic brake device  160  is configured so as to have two end parts  164 , that is, so as to have two magnetic poles. In other words, in the present embodiment, by having two magnetic poles, the electromagnetic brake device  160  is configured as a split brake. According to this configuration, for example, when driving the electromagnetic brake device  160 , the control device can control the application of current to the coils  163  so that these two magnetic poles function respectively as the N pole and S pole and the magnetic flux becomes approximately zero in the region near the approximate center of the mold  110  in the width direction (that is, X-axis direction). The region where the magnetic flux is substantially zero is the region where electromagnetic force is substantially not imparted to the molten steel  2 . This is a region in which so-called escape of the flow of molten steel released from the braking force by the electromagnetic brake device  160  can be achieved. By such a region being achieved, it becomes possible to deal with a broader range of casting conditions. 
     Note that, in the illustrated example of the configuration, the electromagnetic brake device  160  is configured to have two magnetic poles, but the present embodiment is not limited to such an example. The electromagnetic brake device  160  may also be configured to have three or more end parts  164  and to have three or more magnetic poles. In this case, the amounts of current applied to the coil  163  of the end parts  164  are suitably adjusted, whereby application of electromagnetic force to the molten steel  2  according to the electromagnetic brake can be further controlled in detail. 
     2-2. Details of Position of Placement of Electromagnetic Force Generating Device 
     The heights of the electromagnetic stirring device  150  and electromagnetic brake device  160  and the set positions of the electromagnetic stirring device  150  and electromagnetic brake device  160  in the Z-axis direction will be explained. 
     In the electromagnetic stirring device  150  and the electromagnetic brake device  160 , the greater the respective heights of the electromagnetic stirring core  152  and electromagnetic brake core  162 , the higher the performance in imparting an electromagnetic force that can be said. For example, the performance of the electromagnetic brake device  160  depends on the cross-sectional area of the end part  164  of the electromagnetic brake core  162  in the X-Z plane (height H 2  in Z-axis direction×width W 2  in X-axis direction), the value of the DC current applied, and the number of turns of the coil  163 . Therefore, when setting both of the electromagnetic stirring device  150  and electromagnetic brake device  160  at the mold  110 , the installation position of the electromagnetic stirring core  152  and electromagnetic brake core  162  in the limited installation space, more specifically how to set the ratio of heights of the electromagnetic stirring core  152  and the electromagnetic brake core  162  is extremely important from the viewpoint of more effectively drawing out the performances of the devices for improving the quality of the cast slab  3 . 
     Here, as disclosed in the above PTLs 1 and 2 as well, in the past, the method of using both an electromagnetic stirring device and an electromagnetic brake device in continuous casting has been proposed. However, in actuality, even if combining an electromagnetic stirring device and an electromagnetic brake device, the quality of the cast slab ends up deteriorating in quite a few cases compared with when using the electromagnetic stirring device or the electromagnetic brake device alone. This is because the strong points of both devices are not simply obtained if just providing both devices. Depending on the configurations of the devices and set positions etc., the respective strong points can end up cancelling each other out. In PTLs 1 and 2 as well, the specific hardware configurations are not clearly shown. The heights of the cores of the two devices are also not clearly shown. That is, with the conventional method, it cannot be said that the effect of improvement of the quality of the cast slab can be sufficiently obtained by providing both of the electromagnetic stirring device and electromagnetic brake device. 
     As opposed to this, in the present embodiment, as explained above, the ratio of suitable heights of the electromagnetic stirring core  152  and electromagnetic brake core  162  is prescribed so that the quality of the cast slab  3  can be achieved even with high speed casting. Due to this, it becomes possible to achieve the quality of the cast slab  3  while improving the productivity. 
     Here, the casting speed in continuous casting greatly differs depending on the size of the cast slab or the type of product, but in general is 0.6 to 2.0 m/min or so. Continuous casting exceeding 1.6 m/min is called “high speed casting”. In the past, for automobile use external panels etc. where high quality is demanded, with high speed casting with a casting speed of over 1.6 m/min, securing the quality is difficult, so 1.4 m/min or so is the general casting speed. 
     Therefore, in the present embodiment, in consideration of the above situation, for example, even at high speed casting with a casting speed of over 1.6 m/min, securing a quality of the cast slab  3  equal to or better than that when performing continuous casting by a conventional slower casting speed is set as a specific target. Below, the ratio of heights of the electromagnetic stirring core  152  and electromagnetic brake core  162  in the present embodiment enabling this target to be satisfied will be explained in detail. 
     As explained above, in the present embodiment, to secure space for setting the electromagnetic stirring device  150  and electromagnetic brake device  160  at the center part of the mold  110  in the Z-axis direction, the water boxes  130 ,  140  are placed above and below the mold  110 . Here, even if the electromagnetic stirring core  152  is positioned above from the surface of the molten steel, it is not possible to obtain that effect. Therefore, the electromagnetic stirring core  152  should be arranged below the surface of the molten steel. Further, to effectively apply the magnetic field to the discharge flow, the electromagnetic brake core  162  is preferably positioned near the discharge holes of the submerged nozzle  6 . In arranging the water boxes  130 ,  140  in this way, the discharge holes of the submerged nozzle  6  become positioned above the lower water box  140 , so the electromagnetic brake core  162  should be set above from the lower water box  140 . Therefore, the height H 0  of the space at which the effect is obtained by setting the electromagnetic stirring core  152  and electromagnetic brake core  162  (below, also referred to as the “effective space”) becomes the height from the surface of the molten steel to the top end of the lower water box  140  (see  FIG. 2 ). 
     In the present embodiment, to make the most effective use of this effective space, the electromagnetic stirring core  152  is set so that the top end of the electromagnetic stirring core  152  becomes substantially the same height as the surface of the molten steel. At this time, if expressing the height of the electromagnetic stirring core  152  of the electromagnetic stirring device  150  as H 1 , the height of the case  151  as H 3 , the height of the electromagnetic brake core  162  of the electromagnetic brake device  160  as H 2 , and the height of the case  161  as H 4 , the following numerical formula (1) stands. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
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                     + 
                     
                       
                         
                           H 
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                         - 
                         
                           H 
                           ⁢ 
                           
                               
                           
                           ⁢ 
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                       ⁢ 
                       
                           
                       
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                   = 
                   
                     
                       
                         
                           
                             H 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             H 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
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                         2 
                       
                       + 
                       
                         H 
                         ⁢ 
                         
                             
                         
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                         4 
                       
                     
                     ≤ 
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       0 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In other words, it is necessary to satisfy the above numerical formula (1) while prescribing the ratio H 1 /H 2  between the height H 1  of the electromagnetic stirring core  152  and the height H 2  of the electromagnetic brake core  162  (below, also referred to as the “core height ratio H 1 /H 2 ”). Below, the heights H 0  to H 4  will be respectively explained. 
     Regarding Height H 0  of Effective Space 
     As explained above, in the electromagnetic stirring device  150  and electromagnetic brake device  160 , the greater the heights of the electromagnetic stirring core  152  and electromagnetic brake core  162 , the higher the performance in imparting an electromagnetic force which can be said. Therefore, in the present embodiment, the molding facility  10  is configured so that the height H 0  of the effective space becomes as large as possible so that the two devices can better exert their performances. Specifically, to increase the height H 0  of the effective space, it is sufficient to enlarge the length of the mold  110  in the Z-axis direction. On the other hand, as explained above, considering the coolability of the cast slab  3 , the length from the surface of the molten steel to the bottom end of the mold  110  is preferably 1000 mm or so or less. Therefore, in the present embodiment, to achieve the coolability of the cast slab  3  while increasing the height H 0  of the effective space as much as possible, the mold  110  is formed so that the length from the surface of the molten steel to the bottom end of the mold  110  becomes 1000 mm or so. 
     Here, if trying to configure the lower water box  140  so as to be able to store an amount of water enough for a sufficient cooling capability to be obtained, based on past results of operations etc., the height of the lower water box  140  has to be at least 200 mm or so. Therefore, the height H 0  of the effective space is 800 mm or so or less. 
     Regarding Heights H 3 , H 4  of Cases of Electromagnetic Stirring Device and Electromagnetic Brake Device 
     As explained above, the coil  153  of the electromagnetic stirring device  150  is formed by winding a conductor with a cross-sectional size of 10 mm×10 mm or so in two to four layers around an electromagnetic stirring core  152 . Therefore, the height of the electromagnetic stirring core  152  including up to the coil  153  becomes H 1 +80 mm or so or more. If considering the space between the inside wall of the case  151  and the electromagnetic stirring core  152  and coil  153 , the height H 3  of the case  151  becomes H 1 +200 mm or so or more. 
     For the electromagnetic brake device  160  as well, in the same way, the height of the electromagnetic brake core  162  including up to the coil  163  becomes H 2 +80 mm or so or more. If considering the space between the inside wall of the case  161  and the electromagnetic brake core  162  and coil  163 , the height H 4  of the case  161  becomes H 2 +200 mm or so or more. 
     Range which H 1 +H 2  can Take 
     If entering the values of the above-mentioned H 0 , H 3 , and H 4  in the above numerical formula (1), the following numerical formula (2) is obtained.
 
[Mathematical 4]
 
 H 1+ H 2≤500 mm  (2)
 
     That is, the electromagnetic stirring core  152  and electromagnetic brake core  162  have to be configured so that the sum of the heights H 1 +H 2  becomes 500 mm or so or less. Below, the suitable core height ratio H 1 /H 2  satisfying the above numerical formula (2) while sufficiently obtaining the effect of improvement of the quality of the cast slab  3  will be studied. 
     Regarding Core Height Ratio H 1 /H 2   
     In the present embodiment, the suitable range of the core height ratio H 1 /H 2  is set by prescribing the range of height H 1  of the electromagnetic stirring core  152  by which the effect of electromagnetic stirring can be more reliably obtained. 
     As explained above, in electromagnetic stirring, by making the molten steel  2  flow at the interface of the solidified shell, a cleaning effect is obtained of keeping impurities from being trapped at the solidified shell  3   a  and the surface quality of the cast slab  3  can be improved. On the other hand, the further downward in the mold  110 , the greater the thickness of the solidified shell  3   a  inside the mold  110 . The effect of electromagnetic stirring extends to the unsolidified part  3   b  at the inside of the solidified shell  3   a , so the height H 1  of the electromagnetic stirring core  152  can be determined by to what extent of thickness the surface quality of the cast slab  3  has to be achieved. 
     Here, in a type of product with tough demands on surface quality, often a process is performed of grinding the surface layer of the cast slab  3  after casting down by a few millimeters. The depth of grinding is 2 mm to 5 mm or so. Therefore, in such a type of product with tough demands on surface quality, even if performing electromagnetic stirring in a range of thickness of the solidified shell  3   a  smaller than 2 mm to 5 mm in the mold  110 , the surface layer of the cast slab  3  reduced in impurities by this electromagnetic stirring ends up being removed by a subsequent grinding process. In other words, if not performing electromagnetic stirring in a range of thickness of the solidified shell  3   a  of 2 mm to 5 mm or more in the mold  110 , the effect of improvement of the surface quality at the cast slab  3  cannot be obtained. 
     It is known that the solidified shell  3   a  gradually grows from the surface of the molten steel and the thickness is shown by the following numerical formula (3). Here, δ is the thickness of the solidified shell  3   a  (m), “k” is a constant dependent on the cooling ability, “x” is the distance from the surface of the molten steel (m), and Vc is the casting speed (m/min). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
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                   δ 
                   = 
                   
                     k 
                     ⁢ 
                     
                       
                         x 
                         Vc 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     From the above numerical formula (3), the relationship between the casting speed (m/min) and the distance from the surface of the molten steel in the case where the thickness of the solidified shell  3   a  becomes 4 mm or 5 mm was found.  FIG. 7  shows the results.  FIG. 7  is a view showing the relationship between the casting speed (m/min) and distance from the surface of the molten steel (mm) in the case where the thickness of the solidified shell  3   a  becomes 4 mm or 5 mm. In  FIG. 7 , the casting speed is taken along the abscissa while the distance from the surface of the molten steel is taken along the ordinate. The relationship between the two is plotted when the thickness of the solidified shell  3   a  becomes 4 mm and thickness of the solidified shell  3   a  becomes 5 mm. Note that, in the calculations when obtaining the results shown in  FIG. 7 , the value corresponding to the general mold was made k=17. 
     For example, from the results shown in  FIG. 7 , it will be understood that if the thickness ground down is smaller than 4 mm and the molten steel  2  may be electromagnetically stirred in a range of thickness of the solidified shell  3   a  of up to 4 mm, by making the height H 1  of the electromagnetic stirring core  152  200 mm, the effect of electromagnetic stirring is obtained in continuous casting by a casting speed of 3.5 m/min or less. It will be understood that if the thickness ground down is smaller than 5 mm and the molten steel  2  may be electromagnetically stirred in a range of thickness of the solidified shell  3   a  of up to 5 mm, by making the height H 1  of the electromagnetic stirring core  152  300 mm, the effect of electromagnetic stirring is obtained in continuous casting by a casting speed of 3.5 m/min or less. Note that, the value of “3.5 m/min” of the casting speed corresponds to the maximum casting speed possible in operation and equipment in general continuous casting machines. 
     Here, as explained above, in the present embodiment, for example, the aim is to achieve a quality of the cast slab  3  equal to the case of performing continuous casting by a conventional slower casting speed even in high speed casting with a casting speed exceeding 1.6 m/min. If the casting speed exceeds 1.6 m/min, to obtain the effect of electromagnetic stirring even if the thickness of the solidified shell  3   a  becomes 5 mm, from  FIG. 7 , it is learned that the height H 1  of the electromagnetic stirring core  152  has to be made at least about 150 mm or more. 
     From the results of the above studies, in the present embodiment, the electromagnetic stirring core  152  is configured so that the height H 1  of the electromagnetic stirring core  152  becomes about 150 mm or more so as to obtain the effect of electromagnetic stirring even if the thickness of the solidified sheet  3   a  becomes 5 mm in, for example, continuous casting at a relatively high speed of a casting speed of over 1.6 m/min. 
     Regarding the height H 2  of the electromagnetic brake core  162 , as explained above, the greater the height H 2 , the higher the performance of the electromagnetic brake device  160 . Therefore, it is sufficient to find the range of H 2  corresponding to the range of height H 1  of the electromagnetic stirring core  152  in the case where H 1 +H 2 =500 mm from the above numerical formula (2). That is, the height H 2  of the electromagnetic brake core  162  is about 350 mm. 
     From the values of the height H 1  of the electromagnetic stirring core  152  and the height H 2  of the electromagnetic brake core  162 , the core height ratio H 1 /H 2  of the present embodiment becomes, for example, the following numerical formula (4). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   0.43 
                   ≤ 
                   
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Summarizing this, in the present embodiment, when aiming at securing a quality of the cast slab  3  equal to or better than when performing continuous casting by a conventional lower casting speed even when exceeding a casting speed of 1.6 m/min, for example, the electromagnetic stirring core  152  and the electromagnetic brake core  162  are configured so that the height H 1  of the electromagnetic stirring core  152  and the height H 2  of the electromagnetic brake core  162  satisfy the above numerical formula (4). 
     Note that, the preferable upper limit value of the core height ratio H 1 /H 2  can be prescribed by the smallest value which the height H 2  of the electromagnetic brake core  162  can take. This is because the smaller the height H 2  of the electromagnetic brake core  162 , the larger the core height ratio H 1 /H 2  becomes, but if the height H 2  of the electromagnetic brake core  162  is too small, the electromagnetic brake will not effectively function and the effect of improvement of the quality of the cast slab  3  by the electromagnetic brake, in particular, the inside quality, can no longer be obtained. The smallest value of the height H 2  of the electromagnetic brake core  162  at which the effect of the electromagnetic brake can be sufficiently obtained differs according to the size of the cast slab, the type of product, the casting speed, and other casting conditions. Therefore, the smallest value of the height H 2  of the electromagnetic brake core  162 , that is, the upper limit value of the core height ratio H 1 /H 2 , can for example be prescribed based on simulation by numerical analysis simulating the casting conditions in actual operations such as shown in Examples 1 to 3 and actual machine tests etc. 
     Above, the configuration of the molding facility  10  according to the present embodiment was explained. Note that, in the above explanation, when obtaining the relationship shown in the above numerical formula (4), the relationship was obtained assuming H 1 +H 2 =500 mm from the above numerical formula (2). However, the present embodiment is not limited to such an example. As explained above, to draw out the performance of the device more, H 1 +H 2  is preferably as large as possible, so in the above example, H 1 +H 2 =500 mm was set. On the other hand, for example, considering the work efficiency when installing the water boxes  130 ,  140 , electromagnetic stirring device  150 , and electromagnetic brake device  160  etc., sometimes it may be preferable that there be clearance between these members in the Z-axis direction. If stressing more the work efficiency and other such factors in this way, it is not necessarily required that H 1 +H 2 =500 mm. For example, the core height ratio H 1 /H 2  may be set using H 1 +H 2 =450 mm or H 1 +H 2  being another value smaller than 500 mm. 
     Further, in the above explanation, when the casting speed would exceed 1.6 m/min, as a condition for obtaining the effect of the electromagnetic stirring even if the thickness of the solidified shell  3   a  becomes 5 mm, from  FIG. 7 , the smallest value of about 150 mm of the height H 1  of the electromagnetic stirring core  152  was found and the value of the core height ratio H 1 /H 2  at that time of 0.43 was made the lower limit value of that core height ratio H 1 /H 2 . However, the present embodiment is not limited to such an example. If the targeted casting speed is set faster, the lower limit value of the core height ratio H 1 /H 2  may also change. That is, in actual operation, at the targeted casting speed, the smallest value of the height H 1  of the electromagnetic stirring core  152  where the effect of electromagnetic stirring is obtained even if the thickness of the solidified shell  3   a  becomes 5 mm may be found from  FIG. 7  and the core height ratio H 1 /H 2  corresponding to that value of H 1  may be made the lower limit value of the core height ratio H 1 /H 2 . 
     As one example, considering the work efficiency etc., it was tried to find the condition of the core height ratio H 1 /H 2  in the case of targeting securing a quality of the cast slab  3  equal to or better than the case of making H 1 +H 2 =450 mm and performing continuous casting by a casting speed lower than the conventional lower speed casting speed even at a faster casting speed of 2.0 m/min. First, from  FIG. 7 , the condition is found for obtaining the effect of electromagnetic stirring even if the thickness of the solidified shell  3   a  becomes 5 mm in the case where the casting speed is 2.0 m/min or more. Referring to  FIG. 7 , when the casting speed is 2.0 m/min, at a position of a distance from the surface of the molten steel of about 175 mm. the thickness of the solidified shell becomes 5 mm. Therefore, if considering the margin, even if the thickness of the solidified shell  3   a  becomes 5 mm, the smallest value of the height H 1  of the electromagnetic stirring core  152  where the effect of electromagnetic stirring can be obtained is found to be 200 mm or so. At this time, since H 1 +H 2 =450 mm, H 2 =250 mm, so the condition found for the core height ratio H 1 /H 2  is expressed by the following numerical formula (5). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   0.80 
                   ≤ 
                   
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       H 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     That is, in the present embodiment, when aiming at securing a quality of the cast slab  3  equal to or better than the case of performing continuous casting by a conventional lower speed casting speed even at a casting speed of 2.0 m/min, it is sufficient be configure the electromagnetic stirring core  152  and electromagnetic brake core  162  so as to at least satisfy the above numerical formula (5). Note that regarding the upper limit value of the core height ratio H 1 /H 2 , as explained above, this may be prescribed based on simulation by numerical analysis simulating the casting conditions in actual operations and on actual machine tests etc. 
     In this way, in the present embodiment, the range of the core height ratio H 1 /H 2  enabling a quality of the cast slab (surface quality and inside quality) equal to or better than conventional lower speed continuous casting even when making the casting speed increase can change in accordance with the specific value of the casting speed targeted and the specific value of H 1 +H 2 . Therefore, when setting a suitable range of the core height ratio H 1 /H 2 , it is sufficient to suitably set target values of the casting speed and H 1 +H 2  considering the casting conditions at the time of actual operation and the configuration of the continuous casting machine  1  etc. and suitably find a suitable range of the core height ratio H 1 /H 2  at that time by the method explained above. 
     Example 1 
     Simulation by numerical analysis was performed for confirming that the surface quality of the cast slab can be achieved by applying the present invention even if making the casting speed increase. In this simulation by numerical analysis, a calculation model was prepared simulating a cast mold facility  10  in which an electromagnetic force generating device  170  is placed according to the present embodiment explained with reference to  FIG. 2  to  FIG. 5  and the behavior of the molten steel and Ar gas bubbles in the molten steel during the continuous casting was calculated. The conditions of the simulation by numerical analysis were as follows: 
     Conditions of Simulation by Numerical Analysis 
     Width W 1  of electromagnetic stirring core of electromagnetic stirring device: 1900 mm 
     Current application conditions of electromagnetic stirring device: 680 A, 3.0 Hz 
     Number of turns of coil of electromagnetic stirring device: 20 turns 
     Width W 2  of electromagnetic brake core of electromagnetic brake device: 500 mm 
     Distance W 3  between electromagnetic brake cores of electromagnetic brake device: 350 mm 
     Current application conditions of electromagnetic brake device: 900 A 
     Number of turns of coil of electromagnetic brake device: 120 turns 
     Casting speed: 1.4 m/min or 2.0 m/min 
     Mold width: 1600 mm 
     Mold thickness: 250 mm 
     Amount of Ar gas blown: 5 NL/min 
     In evaluation of the surface quality, fluid simulations were run under the above conditions to calculate the flow rate of the molten steel, the solidification speed of the molten steel, and the distribution of Ar gas bubbles in the molten steel of the continuous casting machine and evaluate the Ar gas bubbles trapped at the solidified shell. Specifically, the probability P g  of the Ar gas bubbles being trapped at the solidified shell was calculated by the function shown in the following numerical formula (6). Here, C 0  is a constant, while U is the flow rate of molten steel at the solidification interface.
 
[Mathematical 8]
 
 P   g =exp(− C   0   U   (6)
 
     Further, the speed η g  by which Ar gas bubbles are trapped at the solidified sheet at this time was calculated using the following numerical formula (7). Here, n g  is the number density of Ar gas bubbles at the solidified shell interface, while R s  is the solidification speed of the solidified shell.
 
[Mathematical 9]
 
η g =η g   R   s   P   g   (7)
 
     Further, the number density S g  of the Ar gas bubbles in the solidified shell was calculated using the following numerical formula (8). Here, U s  is the speed of movement of the solidified shell in the direction of pull out of the cast slab. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           S 
                           g 
                         
                       
                       
                         δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         t 
                       
                     
                     + 
                     
                       ∇ 
                       
                         · 
                         
                           ( 
                           
                             
                               U 
                               s 
                             
                             ⁢ 
                             
                               S 
                               g 
                             
                           
                           ) 
                         
                       
                     
                   
                   = 
                   
                     η 
                     g 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     The number density S g  of the Ar gas bubbles in the solidified shell calculated from the above numerical formula (8) was averaged over time and the number of Ar gas bubbles of a diameter of 1 mm trapped within a range of 4 mm from the surface layer of the cast slab was calculated as the pinhole index. The smaller the pinhole index, the higher the surface quality of the cast slab which can be said. Note that for details of the method of evaluation of the surface quality of a cast slab by the simulation by numerical analysis explained above, it is possible to refer to the prior application by the present applicant shown in Japanese Unexamined Patent Publication No. 2015-157309. 
     Note that, in the evaluation of the surface quality, simulation was performed based on the relationship shown in the above numerical formula (2) by the eight combinations of the height H 1  of the electromagnetic stirring core and the height H 2  of the electromagnetic brake core shown in the following Table 1 giving H 1 +H 2 =500 mm. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 H1 (mm) 
                 150 
                 200 
                 225 
                 250 
                 300 
                 350 
                 375 
                 400 
               
               
                 H2 (mm) 
                 350 
                 300 
                 275 
                 250 
                 200 
                 150 
                 125 
                 100 
               
               
                 H1/H2 
                 0.43 
                 0.67 
                 0.82 
                 1.00 
                 1.50 
                 2.33 
                 3.00 
                 4.00 
               
               
                   
               
            
           
         
       
     
     Further, for comparison, the surface quality of a cast slab when only an electromagnetic stirring device is set as one example of a conventional continuous casting method was also evaluated. The conventional continuous casting method evaluated corresponds to a continuous casting method using the molding facility  10  shown in  FIG. 2  to  FIG. 5  from which the electromagnetic brake device  160  has been removed. Further, in the calculations regarding the conventional continuous casting method, the height H 1  of the electromagnetic stirring core was fixed at 250 mm. For the conventional continuous casting method, the pinhole index was calculated by a method similar to the method of calculation explained above except that no electromagnetic brake device  160  is set and that the height H 1  of the electromagnetic stirring core was fixed at 250 mm. 
     The results of simulation of the surface quality by numerical analysis are shown in  FIG. 8  and  FIG. 9 .  FIG. 8  is a graph showing the relationship between the core height ratio H 1 /H 2  and the pinhole index in the case where the casting speed is 1.4 m/min obtained by simulation by numerical analysis.  FIG. 9  is a graph showing the relationship between the core height ratio H 1 /H 2  and the pinhole index in the case where the casting speed is 2.0 m/min obtained by simulation by numerical analysis. In  FIG. 8  and  FIG. 9 , the core height ratio H 1 /H 2  is taken along the abscissa while the pinhole index is taken along the ordinate and the relationship of the two is plotted. Further, in  FIG. 8  and  FIG. 9 , the value of the pinhole index in the above conventional continuous casting method is shown by the broken line parallel to the abscissa. 
     Referring to  FIG. 8 , if the casting speed is 1.4 m/min, the pinhole index in the conventional continuous casting method is 40 or so. On the other hand, in the continuous casting method according to the present embodiment, when the core height ratio H 1 /H 2  is 0.82 or more, a pinhole index as much as up to the level of the conventional continuous casting method is obtained. In particular, if the core height ratio H 1 /H 2  becomes 1.0 or more, the pinhole index falls from the conventional continuous casting method. Further, the pinhole index falls the larger the value of the core height ratio H 1 /H 2 . That is, it is believed that the larger the height H 1  of the electromagnetic stirring core  152  with respect to the height H 2  of the electromagnetic brake core  162 , the more the pinhole index falls and the better the surface quality of the cast slab  3  becomes. 
     Referring to  FIG. 9 , if making the casting speed increase up to 2.0 m/min, the pinhole index in the conventional continuous casting method deteriorates to 80 or so. On the other hand, in the continuous casting method according to the present embodiment, if the core height ratio H 1 /H 2  is about 0.70 to about 2.70, the pinhole index falls to equal to or less than the conventional continuous casting method. In particular, if the core height ratio H 1 /H 2  is about 1.0 to about 1.5, the pinhole index decreases to 40 or so. It is learned that even if making the casting speed increase to 2.0 m/min, it is possible to obtain a surface quality equal to the case of performing continuous casting by the conventional continuous casting method by a casting speed of 1.4 m/min. 
     From the above results, it was learned that under the casting conditions corresponding to the conditions of the above simulation by numerical analysis, if making the core height ratio H 1 /H 2  any value between about 0.70 to about 2.70, it becomes possible to achieve a surface quality of the cast slab equal to or better than that of a conventional continuous casting method in continuous casting with at least a casting speed of 1.4 m/min to 2.0 m/min. In particular, it was learned that if making the core height ratio H 1 /H 2  about 1.0 to about 1.5, even if making the casting speed increase to 2.0 m/min, it becomes possible to obtain a surface quality of the cast slab equal to or better than that of a conventional lower speed (specifically, casting speed 1.4 m/min) continuous casting method. 
     Example 2 
     To confirm that the inside quality of the cast slab can be achieved by application of the present invention even if making the casting speed increase, simulation by numerical analysis was performed. Regarding the inside quality, a method of simulation similar to that when evaluating the surface quality explained above was used except that rather than Ar gas bubbles, the value of residual alumina, which is a typical impurity inclusion in a cast slab, present in the cast slab was evaluated. Specifically, a vertical curved type continuous casting machine was presumed, the behavior of alumina particles during the continuous casting was analyzed by simulation, the alumina particles descending from the vertical part were deemed remaining at the cast slab as they are, and the number of alumina particles in a predetermined volume of the cast slab was calculated as the inside quality index. At that time, the length of the vertical part of the continuous casting machine was made 3 m. Further, the diameter of the alumina particles was deemed 0.4 mm and the specific gravity of the alumina particles was deemed 3990 kg/m 3 . The smaller the inside quality index, the higher the inside quality of the cast slab can be said. 
     Note that, in evaluation of the inside quality, the height H 1  of the electromagnetic stirring core and the height H 2  of the electromagnetic brake core were simulated based on the relationship shown in numerical formula (2) for the four combinations shown in the following Table 2 giving H 1 +H 2 =450 mm: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 H1 (mm) 
                 200 
                 250 
                 270 
                 300 
               
               
                   
                 H2 (mm) 
                 250 
                 200 
                 180 
                 150 
               
               
                   
                 H1/H2 
                 0.80 
                 1.25 
                 1.50 
                 2.00 
               
               
                   
                   
               
            
           
         
       
     
     Further, regarding the inside quality as well, for comparison, as one example of a conventional continuous casting method, the inside quality in the case of only the electromagnetic stirring device being installed was also evaluated. The evaluated conventional continuous casting method was a continuous casting method using the molding facility  10  according to the present embodiment shown in  FIG. 2  to  FIG. 5  in the same way as the time of evaluation of the above-mentioned surface quality but with the electromagnetic brake device  160  removed. Further, the electromagnetic stirring core height H 1  of the electromagnetic stirring device was fixed at 250 mm. 
     The results of simulation by numerical analysis of the inside quality are shown in  FIG. 10 .  FIG. 10  is a graph showing the relationship between the casting speed and inside quality index obtained by simulation by numerical analysis. In  FIG. 10 , the casting speed is taken along the abscissa, while the inside quality index is taken along the ordinate. The relationship of the casting speed and inside quality index corresponding to the values of the core height ratio H 1 /H 2  shown in Table 2 is plotted. Further, in  FIG. 10 , the results by the above conventional continuous casting method are also plotted. 
     Referring to  FIG. 10 , in the conventional continuous casting method, the inside quality index in the case of a general casting speed of 1.4 m/min is about 40. This inside quality index remarkably increases as the casting speed increases (that is, the inside quality of the cast slab remarkably deteriorates as the casting speed increases). 
     On the other hand, in the continuous casting method according to the present embodiment, when the core height ratio H 1 /H 2  is 1.5 or less, even if making the casting speed increase to 2.0 m/min or so, the inside quality index is kept smaller than 40. An inside quality better than the case of the conventional continuous casting method where the casting speed is 1.4 m/min can be obtained. Even if the core height ratio H 1 /H 2  is 2.0, if the casting speed is 2.4 m/min, the inside quality index is about 60. It is possible to achieve an inside quality equal to the case in the conventional continuous casting method where the casting speed is 1.6 m/min. From the above results, to achieve the inside quality of the cast slab as much as up to the level of the past even if making the casting speed a high speed, the core height ratio H 1 /H 2  may be made 2.0 or less, more preferably 1.5 or less. 
     From the above results, it was learned that if making the core height ratio H 1 /H 2  about 1.5 or less in the casting conditions corresponding to the conditions of simulation by numerical analysis, in continuous casting by a casting speed of 2.0 m/min, it becomes possible to achieve an inside quality of the cast slab as much as up to the level of the conventional continuous casting method at a casting speed of 1.4 m/min. Further, if making the core height ratio H 1 /H 2  any value of about 2.0 or less, in continuous casting by a casting speed of 2.4 m/min, it becomes possible to achieve an inside quality of the cast slab as much as up to the level of the conventional continuous casting method at a casting speed of 1.6 m/min. 
     Example 3 
     To further confirm the advantageous effect of the present invention, an actual machine test was run. In this actual machine test, the electromagnetic force generating device  170  according to the present embodiment explained with reference to  FIG. 2  to  FIG. 5  was installed at a continuous casting machine being actually used for operations and that continuous casting machine was used for actual continuous casting while changing the core height ratio H 1 /H 2  and casting speed in various ways. Further, the cast slab which was cast was investigated for surface quality and inside quality visually and by ultrasonic flaw detection. Further, for comparison, continuous casting was performed and the quality of the cast slab was evaluated by a similar method for a conventional continuous casting method in which only an electromagnetic stirring device was set. The conventional continuous casting method is a continuous casting method configured, in the same way as the time of simulation by numerical analysis explained above, like the molding facility  10  according to the present embodiment shown in  FIG. 2  to  FIG. 5  except with the electromagnetic brake device  160  removed. Further, the casting speed in the conventional continuous casting method was made 1.6 m/min, while the height of the electromagnetic stirring core of the electromagnetic stirring device was made 200 mm. 
     Further, regarding the submerged nozzle, in both the present embodiment and the conventional continuous casting method, one with discharge holes facing downward at 45° was used. The depth of the tips of the discharge holes from the surface of the molten steel was made 270 mm. 
     The results are shown in the following Table 3. In Table 3, the quality of the cast slab is expressed, with reference to the quality in the conventional continuous casting method, as “G (Good)” when a quality better than that conventional continuous casting method is obtained, as “F (Fair)” when a quality of the same extent as that conventional continuous casting method is obtained, and as “P (Poor)” when a quality worse than that conventional continuous casting method is obtained. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                   
                   
                   
                   
                 Electro- 
                 Electro- 
                 Electro- 
                   
                   
               
               
                   
                   
                   
                   
                 magnetic 
                 magnetic 
                 magnetic 
                 Core 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Casting 
                 Electromagnetic stirring 
                 brake 
                 stirring 
                 brake 
                 height 
                 Quality of cast slab 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Con- 
                 speed 
                 Current 
                 Frequency 
                 Magnetic flux 
                 core height 
                 core height 
                 ratio 
                 Surface 
                 Inside 
               
               
                 dition 
                 (m/min) 
                 (A) 
                 (Hz) 
                 (T) 
                 H1(mm) 
                 H2(mm) 
                 H1/H2 
                 quality 
                 quality 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 200 
                 250 
                 0.80 
                 G 
                 G 
               
               
                 2 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 200 
                 250 
                 0.80 
                 G 
                 G 
               
               
                 3 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 200 
                 250 
                 0.80 
                 G 
                 G 
               
               
                 4 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 200 
                 250 
                 0.80 
                 F 
                 G 
               
               
                 5 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 200 
                 250 
                 0.80 
                 P 
                 F 
               
               
                 6 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 200 
                 250 
                 0.80 
                 P 
                 P 
               
               
                 7 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 250 
                 250 
                 1.00 
                 G 
                 G 
               
               
                 8 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 250 
                 250 
                 1.00 
                 G 
                 G 
               
               
                 9 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 250 
                 250 
                 1.00 
                 G 
                 G 
               
               
                 10 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 250 
                 250 
                 1.00 
                 G 
                 G 
               
               
                 11 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 250 
                 250 
                 1.00 
                 F 
                 F 
               
               
                 12 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 250 
                 250 
                 1.00 
                 P 
                 P 
               
               
                 13 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 250 
                 200 
                 1.25 
                 G 
                 G 
               
               
                 14 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 250 
                 200 
                 1.25 
                 G 
                 G 
               
               
                 15 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 250 
                 200 
                 1.25 
                 G 
                 G 
               
               
                 16 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 250 
                 200 
                 1.25 
                 G 
                 G 
               
               
                 17 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 250 
                 200 
                 1.25 
                 F 
                 F 
               
               
                 18 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 250 
                 200 
                 1.25 
                 P 
                 P 
               
               
                 19 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 300 
                 200 
                 1.50 
                 G 
                 G 
               
               
                 20 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 300 
                 200 
                 1.50 
                 G 
                 G 
               
               
                 21 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 300 
                 200 
                 1.50 
                 G 
                 G 
               
               
                 22 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 300 
                 200 
                 1.50 
                 G 
                 G 
               
               
                 23 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 300 
                 200 
                 1.50 
                 G 
                 G 
               
               
                 24 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 300 
                 200 
                 1.50 
                 P 
                 P 
               
               
                 25 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 300 
                 150 
                 2.00 
                 G 
                 G 
               
               
                 26 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 300 
                 150 
                 2.00 
                 G 
                 G 
               
               
                 27 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 300 
                 150 
                 2.00 
                 G 
                 G 
               
               
                 28 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 300 
                 150 
                 2.00 
                 G 
                 G 
               
               
                 29 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 300 
                 150 
                 2.00 
                 F 
                 F 
               
               
                 30 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 300 
                 150 
                 2.00 
                 P 
                 P 
               
               
                 31 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 350 
                 150 
                 2.33 
                 G 
                 G 
               
               
                 32 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 350 
                 150 
                 2.33 
                 G 
                 G 
               
               
                 33 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 350 
                 150 
                 2.33 
                 G 
                 G 
               
               
                 34 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 350 
                 150 
                 2.33 
                 F 
                 G 
               
               
                 35 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 350 
                 150 
                 2.33 
                 P 
                 F 
               
               
                 36 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 350 
                 150 
                 2.33 
                 P 
                 P 
               
               
                 37 
                 1.6 
                 680 
                 1.5 
                 0.3 
                 300 
                 100 
                 3.00 
                 G 
                 G 
               
               
                 38 
                 1.8 
                 680 
                 1.5 
                 0.3 
                 300 
                 100 
                 3.00 
                 G 
                 G 
               
               
                 39 
                 2.0 
                 680 
                 1.5 
                 0.3 
                 300 
                 100 
                 3.00 
                 G 
                 F 
               
               
                 40 
                 2.2 
                 680 
                 1.5 
                 0.4 
                 300 
                 100 
                 3.00 
                 F 
                 P 
               
               
                 41 
                 2.4 
                 680 
                 1.5 
                 0.4 
                 300 
                 100 
                 3.00 
                 P 
                 P 
               
               
                 42 
                 2.6 
                 680 
                 1.5 
                 0.4 
                 300 
                 100 
                 3.00 
                 P 
                 P 
               
               
                   
               
            
           
         
       
     
     In the present embodiment, the range of core height ratio H 1 /H 2  enabling a better quality of the cast slab (surface quality and inside quality) than the conventional lower speed (specifically, casting speed ⅙ m/min) continuous casting method to be achieved even if the casting speed is made to increase to 2.0 m/min was investigated. From the results shown in Table 3, it was learned that in the casting conditions corresponding to the above actual machine test, by making the value of the core height ratio H 1 /H 2  about 0.80 to about 2.33, even if making the casting speed increase up to 2.0 m/min, it becomes possible to achieve a quality of the cast slab better than the lower speed conventional continuous casting method. In other words, from the results of the present embodiment, it was shown that by applying the present invention and making the value of the core height ratio H 1 /H 2  about 0.80 to about 2.33, it becomes possible to achieve the quality of the cast slab while making the casting speed increase to up to 2.0 m/min and improving the productivity. Further, in the same way, from the results shown in Table 3, it was learned that in the casting conditions corresponding to the above actual machine test, by making the value of the core height ratio H 1 /H 2  about 1.00 to about 2.00, even if making the casting speed increase up to 2.2 m/min, it becomes possible to achieve a quality of the cast slab better than the lower speed conventional continuous casting method. 
     3. Additional 
     Above, while referring to the attached drawings, preferred embodiments of the present invention were explained in detail, but the present invention is not limited to such examples. A person having ordinary knowledge in the field to which the present invention belongs clearly could conceive of various changes or corrections within the scope of the technical idea described in the claims. It will be understood that these also fall under the technical scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           1  continuous casting machine 
           2  molten steel 
           3  cast slab 
           3   a  solidified shell 
           3   b  unsolidified part 
           4  ladle 
           5  tundish 
           6  submerged nozzle 
           10  molding facility 
           110  mold 
           111  long side mold plate 
           112  short side mold plate 
           121 ,  122 ,  123  backup plate 
           130  upper water box 
           140  lower water box 
           150  electromagnetic stirring device 
           151  case 
           152  electromagnetic stirring core 
           153  coil 
           160  electromagnetic brake device 
           161  case 
           162  electromagnetic brake core 
           163  coil 
           164  end part 
           165  connecting part 
           170  electromagnetic force generating device