Patent Publication Number: US-8124006-B2

Title: Ladle for molten metal delivery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application of PCT/JP2007/055993 filed on Mar. 23, 2007, and claims priority to, and incorporates by reference, Japanese Patent Application Nos. 2006-082515 filed on Mar. 24, 2006 and 2006-123089 filed on Apr. 27, 2006. 
     TECHNICAL FIELD 
     The present invention relates to a pressure-tapping type ladle for transferring molten metal, for use in transferring and supplying melted metals such as molten aluminum to a molten metal-holding furnace in a molten metal-casting facility. 
     BACKGROUND ART 
     When conducting aluminum casting, etc., at a foundry, it is energy inefficient to remelt aluminum solidified into an ingot after being rendered molten by a manufacturer. Therefore, molten metal (melted metal) produced by a manufacturer is delivered to a foundry in molten form using a molten metal-transferring ladle. Examples include the molten metal-transferring ladle disclosed in Patent Document 1. 
     The molten metal-transferring ladle of Patent Document 1 is a pressure-tapping type molten metal-transferring ladle. As shown in  FIG. 11 , the ladle includes a ladle body  101  for containing melted metal; a large lid  102  covering the ladle body  101 , an openable small lid  104  covering an inlet  103  provided in the middle portion of the large lid  102 ; a gas inlet  105  provided with the small lid  104  for pressurizing the surface of the melted metal (the molten metal surface) in the ladle; and a tapping portion  106  provided in the ladle body  101 . The inlet  103  is an opening for use in pouring melted metal into the ladle body  101 , observing the interior, removing aluminum oxide and the like, cleaning, heating by burner, etc. 
     For tapping melted metal, a pressurized gas supplying device is first connected to the gas inlet  105 , and a pressurizing gas is introduced into a molten metal-transferring ladle to pressurize the molten metal surface, thereby supplying melted metal to a local furnace for a die-casting machine, etc., from a tap hole  107  of a tapping portion  106 .
     Patent Document 1: Japanese Unexamined Patent Publication No. 2002-254158   

     DISCLOSURE OF THE INVENTION 
     However, the aforementioned molten metal-transferring ladle has the following drawback. Since the gas inlet is provided on the small lid covering the inlet, the small lid is very heavy. This makes it difficult to open and close the small lid when pouring melted metal into the ladle body, observing the interior, removing aluminum oxide and the like, cleaning, heating by burner, and the like. Another drawback is that since the gas inlet is provided on the small lid covering the inlet formed in the middle of the large lid, it is difficult for the gas inlet to connect with the pressurized gas supplying device, reducing work efficiency. Still another drawback is that since connecting the gas inlet and the pressurizing gas supplying device must be done close to the high-temperature molten metal-transferring ladle containing the molten metal, there is a high risk of getting burned. 
     When a molten metal-transferring ladle containing molten metal is transported to a foundry by a truck or like conveyance, the molten metal surface may undulate greatly due to rough road surfaces or curves taken at street corners. This may cause the molten metal to splash accidentally, causing it to adhere to the gas inlet. The thus-adhered melted metal then cools and solidifies, clogging the gas inlet. This clogging of the gas inlet makes it difficult to guide a pressurizing gas into the molten metal-transferring ladle, and resultantly hinders the tapping of the melted metal. In the worst case, clogging makes it impossible to tap the melted metal. 
     The invention has been made to solve the above-described problems, and aims to provide a pressure-tapping type molten metal-transferring ladle that is safe and that has excellent workability, and can reliably introduce a pressurizing gas. 
     METHODS FOR SOLVING THE PROBLEMS 
     The object of the present invention can be achieved by a molten metal-transferring ladle that includes a ladle body having a storage space for a melted metal, and an opening on the top; a large lid having an inlet in the middle, and covering an upper opening of the ladle body; an openable small lid covering the inlet; a tapping portion communicating the interior with the exterior of the storage space; and a pressurizing gas supplying means supplying a pressurizing gas to the storage space; the large lid including a supplying means installing hole communicating the interior with the exterior of the storage space; and the pressurizing gas supplying means detachably mounted to the supplying means installing hole. 
     It is preferable that the molten metal-transferring ladle further include a supplying means installing device having a handle lever, and a pressurization member communicating with the handle lever via a linkage. It is preferable that the pressurizing gas supplying means detachably mounted to the supplying means installing hole by applying and releasing pressure using the pressurization member along with the operation of the handle lever. 
     It is preferable that the pressurizing gas supplying means extend to the storage space, and include a delivery pipe, the lower portion of which can be immersed in the melted metal retained in the storage space. The delivery pipe is preferably structured to release a pressurizing gas from the lower portion thereof. 
     It is preferable that the delivery pipe include a first regulating member and a second regulating member each provided in the upper portion and the lower portion of the delivery pipe, and a float placed between the first regulating member and the second regulating member. The float may block the delivery pipe when in contact with the first regulating member, whereas the float may not block the delivery pipe when in contact with the second regulating member. 
     It is further preferable that the pressurizing gas supplying means include a discharge hole for discharging the pressurizing gas to the storage space, and a discharge hole protecting member. The discharge hole is preferably provided with the upper portion of the discharge hole protecting member. 
     It is preferable that the pressurizing gas supplying means include a gas discharging portion releasing the pressurizing gas to the storage space. The gas discharging portion is preferably comprised of a gas-permeable fireproof material. 
     It is preferable that the pressuring gas supplying means include a gas discharging portion releasing the pressurizing gas to the storage space. The gas discharging portion is preferably comprised of a gas-permeable fireproof material. 
     EFFECT OF THE INVENTION 
     The present invention can provide a pressure tapping type molten metal-transferring ladle that is safe and has excellent workability, and is capable of reliably introducing a pressurizing gas. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a molten metal-transferring ladle according to one embodiment of the present invention. 
         FIG. 2  is a partial enlarged cross-sectional view of the molten metal-transferring ladle of  FIG. 1 . 
         FIG. 3  is a partial enlarged cross-sectional view showing a modified example of the molten metal-transferring ladle of  FIG. 1 . 
         FIG. 4  is a partial enlarged cross-sectional view showing another modified example of the molten metal-transferring ladle of  FIG. 1 . 
         FIG. 5(   a ) is a cross-sectional view taken along the line A-A of  FIG. 4 , and  FIG. 5(   b ) is a cross-sectional view taken along the line B-B of  FIG. 4 . 
         FIG. 6  is an illustration showing the operation of the molten metal-transferring ladle of  FIG. 4 . 
         FIG. 7  is a partial enlarged cross-sectional view showing a modified example of the molten metal-transferring ladle of  FIG. 4 . 
         FIG. 8  is a partial enlarged cross-sectional view showing another modified example of the molten metal-transferring ladle of  FIG. 1 . 
         FIG. 9  is a cross-sectional view of a double circular tube comprised of the molten metal-transferring ladle of  FIG. 8 . 
         FIG. 10  is a partial enlarged cross-sectional view showing another modified example of the molten metal-transferring ladle of  FIG. 1 . 
         FIG. 11  is a cross-sectional view of a known molten metal-transferring ladle. 
         FIG. 12  is a partial enlarged cross-sectional view showing still another modified example of the molten metal-transferring ladle of  FIG. 1 . 
       
         
           
             
                 
               
                 
                     
                 
                 
                   EXPLANATION OF REFERENCE NUMERALS 
                 
                 
                     
                 
               
              
                 
                     
                 
              
             
             
                 
                 
                 
              
                 
                     
                    1) 
                   molten metal-transferring ladle 
                 
                 
                     
                   10) 
                   ladle body 
                 
                 
                     
                   10a) 
                   top opening 
                 
                 
                     
                   11) 
                   storage space 
                 
                 
                     
                   20) 
                   large lid 
                 
                 
                     
                   24) 
                   inlet 
                 
                 
                     
                   25)  
                   supplying means installing hole 
                 
                 
                     
                   30) 
                   small lid 
                 
                 
                     
                   40) 
                   tapping portion 
                 
                 
                     
                   50) 
                   pressurizing gas supplying means 
                 
                 
                     
                   51) 
                   connecting pipe 
                 
                 
                     
                   52) 
                   connect portion 
                 
                 
                     
                   53) 
                   delivery pipe 
                 
                 
                     
                     
                 
              
             
           
         
       
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereafter, the molten metal-transferring ladle of the invention is explained in detail with reference to the attached drawings.  FIG. 1  shows a cross-sectional view of a molten metal-transferring ladle according to one embodiment of the present invention. As shown in  FIG. 1 , a molten metal-transferring ladle  1  includes a ladle body  10 , a large lid  20 , a small lid  30 , a tapping portion  40 , and a pressurizing gas supplying means  50 . 
     The ladle body  10  is a container including a storage space  11  of molten metal (melted metal), and an opening  10   a  on the top; and is formed by lining an outer shell  12  made from a metal such as steel with a fireproof layer  13  formed of a thermal insulation material and a fireproof material. Examples of thermal insulation materials include heat-insulating bricks, ceramic fiber-type felts, heat-insulating boards, mortar, and the like. Examples of fire-resistant materials include fireproof bricks, castable refractories, plastic refractories, and the like. A pair of fork lift slots  14  are provided with the base of the ladle body  10 . Each fork lift slot  14  of the pair of fork lift slots  14  has a fork pocket  14   a , through which the fork portion of a forklift are inserted. 
     The large lid  20  is a lid covering the top opening  10   a  of the ladle body  10 , and formed by lining the outer shell  22 , made from a metal such as steel, with a fireproof layer  23  formed of the thermal insulation material and fireproof material, as in the ladle body  10  described above. In the middle of the large lid  20 , the inlet  24 , for use in pouring melted metal into the storage space  11  of the ladle body  10 , observing the interior, removing aluminum oxide and the like, cleaning, heating by burner, etc, is provided. The large lid  20  includes a supplying means installing hole  25  communicating the interior with the exterior of the storage space  11 . The supplying means installing hole  25  is located between the periphery of the opening of the inlet  24  and the outer edge of the large lid. 
     A heat-resistant (for example, carbon-based) sealing material, etc. is used to substantially seal the area between the large lid  20  and the ladle body  10 . This sealing is sufficient enough to allow the ladle body inside  10  to withstand the pressure applied when pressurizing gas such as compressed air is supplied to the storage space  11  via the pressurizing gas supplying means  50 . A certain amount of gas leakage is acceptable, insofar as control of the pressure inside the ladle is not hindered. 
     The small lid  30  is an openable lid covering the inlet  24  provided on the large lid  20 , and is formed by lining the outer shell  32 , made from a metal such as steel, with a fireproof layer  33  formed of the thermal insulation material and fireproof material, as in the ladle body  10  mentioned above. A heat-resistant (for example, carbon-based) sealing material, etc. is used to substantially seal the area between the small lid  30  and the large lid  20 . 
     The tapping portion  40  communicates the interior with the exterior of the storage space  11  of the ladle body  10 , and includes a discharging channel  41  that is capable of releasing the melted metal in the storage space  11  to the outside of the ladle body by applying pressure to the storage space inside  11  via the pressurizing gas supplying means  50 , as mentioned later. The discharging channel  41  has an inner diameter of 90 mm, for example. The tapping portion  40  extends upward from the bottom of the ladle body  10 , and a pouring spout  45  is connected to the upper opening of the tapping portion  40 . The pouring spout  45  is bent in two locations so that a discharge opening  46 , from which the melted metal is discharged, faces downward. 
     The pressurizing gas supplying means  50  is a means guiding a gas for pressurizing the molten metal surface of the melted metal in the storage space  11  to the storage space  11 , and is removably provided with the supplying means installing hole  25  formed in the large lid  20  via bolts or the like. As illustrated in a partial enlarged cross-sectional view in  FIG. 2 , the pressurizing gas supplying means  50  includes an L-type connecting pipe  51 , a connect portion  52 , and a delivery pipe  53  to be inserted into the supplying means installing hole  25 . 
     The connecting pipe  51  is connected to a pipe extended from a pressurized gas supplying device (not shown), and mounted on the connect portion  52 . 
     The connect portion  52  is a cylindrical member having an internal space  52   a  and a connecting flange  52   b  that includes bolt-holes for fastening bolts at the outer periphery of the bottom portion. 
     The delivery pipe  53  is a circular pipe member extending toward the storage space  11 . The delivery pipe includes the lower portion  53   b , which can be immersed in the melted metal in the storage space  11 , and the delivery pipe flange  53   a , which is formed at the outer periphery of the upper portion. The delivery pipe flange  53   a  is configured to be in contact with the upper surface of the large lid  20  when the pipe  53  is installed in the supplying means installing hole  25 . 
     When the delivery pipe  53  is made of metal, it is preferable to use a metal pipe coated with a corrosion antioxidant agent, or to apply a fireproof material such as silicone nitride to the surface of the metal tube so that melting damage can be prevented when the pipe touches the melted metal. 
     The delivery pipe  53  may be made of ceramics. Such a composition improves the heat resistance of the delivery pipe  53 , and avoids situations in which the metal of the delivery pipe  53  melts and mixes into the molten metal in the storage space  11 . This maintains the quality of the molten metal in the storage space  11 . 
     The connecting pipe  51 , connect portion  52 , and delivery pipe  53  communicate with each other, and are designed such that a pressurizing gas guided from the pressurized gas supplying device (not shown) passes through the connecting pipe  51 , connect portion  52 , and delivery pipe  53  in that order, and is emitted from the lower portion  53   b  of the delivery pipe  53 . In most cases, air is used as a pressuring gas, but inert gases such as nitrogen gas, argon gas, etc. may also be used. 
     The operation of the embodiment of the molten metal-transferring ladle  1  is explained below. First, the small lid  30  is opened, and melted metal is poured from the inlet  24  to the storage space  11  of the ladle body  10 . After the supplying operation of the melted metal is completed, the small lid  30  is closed. Since the small lid  30  does not include the pressurizing gas supplying means  50 , the lid  30  is light enough to easily open and close. When the melted metal is placed in the storage space  11 , the lower portion  53   b  of the delivery pipe  53  is immersed in the melted metal Z of the storage space  11 . 
     The molten metal-transferring ladle  1  containing the melted metal is transported by a truck or like conveyance to a local furnace for a die-casting machine, etc., where the casting is performed. When a truck, etc., travels on a public road, the molten metal surface of the melted metal may undulate greatly due to the rough road surfaces or curves taken at street corners. This may accidentally splash the melted metal; however, since the lower portion  53   b  of the delivery pipe  53 , from which a pressurizing gas is discharged, is immersed in the melted metal Z, the splashed melted metal will not block the delivery pipe  53 . The melted metal into which the lower portion  53   b  of the delivery pipe  53  is immersed is in a liquid state during transportation, and thus the melted metal will not solidify and clog the delivery pipe  53 . 
     When the melted metal is supplied to a local furnace for a die-casting machine, etc., the pressurized gas supplying device is connected to the pressurizing gas supplying means  50 , thereby introducing a pressurizing gas such as condensed air into the pressurizing gas supplying means  50 . Since the pressurizing gas supplying means  50  is provided on the supplying means installing hole  25  between the periphery of the opening of the inlet  24  formed in the middle of the large lid  20  and the outer edge of the large lid  20 , the pressurizing gas supplying means  50  is within easy reach and can be readily connected with the pressurized gas supplying device. Further, the means do not have to be connected adjacently; i.e., connecting can be conducted at a certain distance from the high-temperature molten metal-transferring ladle  1  containing melted metal, reducing the danger of burns or other injuries. 
     The pressurizing gas supplied into the pressurizing gas supplying means  50  is discharged into the melted metal Z via the delivery pipe  53 , and then moved to the upper surface of the melted metal Z, i.e., a space  1  la, by its buoyancy to pressurize the molten metal surface S of the melted metal. By pressurizing the molten metal surface S, the melted metal Z is pushed out from the tapping portion  40  and then supplied into the local furnace. 
     Since the melted metal entering the delivery pipe  53  is pushed out from the end portion by a pressurizing gas flowing through the delivery pipe  53 , clogging of the delivery pipe  53  caused by the solidified melted metal will not occur. 
     As described above, since the molten metal-transferring ladle  1  of the embodiment includes the pressurizing gas supplying means  50  between the outer edge of the large lid  20  and the periphery of the opening of the inlet  24  formed in the middle of the large lid  20 , rather than the small lid  30 , the small lid  30  can be easily opened and closed for pouring melted metal into the storage space  11  of the ladle body  10 , observing the interior, removing aluminum oxide and the like, cleaning, heating by burner, and the like. Further, when the pipe extending from the pressurized gas supplying device is connected to the pressurizing gas supplying means  50 , the pressurizing gas supplying means  50  is within easy reach, which allows for high work efficiency. Additionally, the connecting operation can be carried out far from the high-temperature molten metal-transferring ladle  1 , avoiding injuries such as burns. 
     Further, the end portion  53   b  of the delivery pipe  53 , from which the pressurizing gas is discharged, is immersed in the melted metal. This setup avoids the clogging of the delivery pipe  53  caused by the solidifying of the melted metal splashed during conveyance. Resultantly, a pressurizing gas can be reliably introduced into the storage space  11 , enabling reliable tapping of the melted metal. 
     Since the gas supplying means  50  is removably provided on the supplying means installing hole  25  that is formed in the large lid  20 , the gas supplying means  50  can, prior to feeding the melted metal into the storage space  11  of the ladle body  10 , be removed from the large lid  20  to check for solidified melted metal adhered to the gas supplying means  50 . Adhered solidified melted metal can be removed ahead of time, if observed. Thus, it is possible to prevent discharge failure from occurring during tapping of the melted metal at the local furnace for a die-casting machine, etc. 
     Although one embodiment of the present invention has been described herein, embodiments of the present invention are not limited thereto. As shown in  FIG. 3 , for example, a gas exhaust hole  53   c  that communicates interior with the exterior of the delivery pipe  53  can be formed on the upper portion of the delivery pipe  53 . According to this configuration, the pressurizing gas is supplied into the storage space  11  via the gas exhaust hole  53   c , and thus the molten metal surface S of the melted metal Z is efficiently pressurized, improving the discharge efficiency of the melted metal. 
     In the embodiment, bolts are used for detachably mounting the pressurizing gas supplying means  50  to the supplying means installing hole  25 . However, the structure is not limited to this, and a one-touch removable coupler may be used for installation, for example. 
     Further, in the present embodiment, the delivery pipe  53  may include a float  61 , a first regulating member  62 , and a second regulating member  63  ( FIG. 4  and  FIG. 5 ).  FIG. 4  is a partial enlarged cross-sectional view of the molten metal-transferring ladle  1 .  FIG. 5(   a ) is a cross-sectional view taken along the line A-A of  FIG. 5 , and  FIG. 5(   b ) is a cross-sectional view taken along the line B-B of  FIG. 5 . 
     The first regulating member  62  and the second regulating member  63  are located at regular intervals in the upper and lower portions of the delivery pipe  53 . The float  61 , which is movable inside the delivery pipe  53 , is contained between the first regulating member  62  and the second regulating member  63 . The first regulating member  62  and the second regulating member  63  are members that limit the movement of the float  61  in the delivery pipe  53 . As illustrated in  FIGS. 4 and 5(   a ), the first regulating member  62  includes at the center of a flat member a round-shaped through-hole  62   a  as seen in a plane view. As shown in  FIG. 5(   b ), the second regulating member  63  is a stick-type member located in the bottom of the delivery pipe  53 , and which partially blocks the flow of the delivery pipe. 
     The float  61  obstructs the delivery pipe  53  when it is in contact with the first regulating member  62 , whereas the float does not block the delivery pipe  53  when it is in contact with the second regulating member  63 . Examples of the float include a spherical member that is floatable in the melted metal contained in the storage space  11 . The float  61  formed of a spherical member is designed to have a diameter small enough to provide a space between the inside wall of the delivery pipe and the float, and larger than that of the through-hole  62   a  provided on the first regulating member  62 . The float  61  is preferably formed into a hollow spherical shape using fireproof materials such as ceramics. 
     In supplying the melted metal into a local furnace for a die-casting machine, a pressurizing gas guided to the connecting pipe  51  and the internal space  52   a  of the connect portion  52  is first directed to the delivery pipe  53 , and then passes through the space between the float  61  and the inner wall of the delivery pipe  53  via the through-hole  62   a  of the first regulating member  62 . The gas is finally released from the lower portion  53   b  of the delivery pipe  53 , thereby reaching the storage space  11 . 
     This configuration reliably prevents the entrance of the melted metal Z into the connecting pipe  51  or connect portion  52 , even when the molten metal surface S of the melted metal Z is greatly inclined relative to the molten metal-transferring ladle  1  when, for example, a truck loaded with a melted metal-containing ladle  1  hits a steep gradient. Hereinafter, details are provided with reference to  FIG. 6 .  FIG. 6  is a partial enlarged cross-sectional view showing a situation in which the molten metal surface S of the melted metal Z is greatly inclined relative to the molten metal-transferring ladle  1 . When the molten metal surface S of the melted metal Z is greatly inclined, the spherical float  61  moves upward in the delivery pipe  53  along with the liquid level change of the melted metal (as indicated by arrow C) to contact the first regulating member  62  that limits the upward movement of the float  61 . In this case, the outer surface of the spherical float  61  is in contact with the inner periphery of the through-hole  62   a  of the first regulating member  62 , which blocks the delivery pipe  53 . This prevents the entry of the melted metal Z, which enters the delivery pipe  53  from the bottom opening of the delivery pipe  53 , into the upper portion of the first regulating member  62 , thereby preventing the entry of the melted metal into the connect portion  52  or connecting pipe  51 , located in the upper portion of the first regulating member  62 . As a result, clogging of the connecting pipe  51  and internal space  52   a  of the connect portion  52 , due to the solidification of the melted metal Z, can be completely prevented, preventing introduction failure of the pressurizing gas into the storage space  11  caused by the clogging of the solidified melted metal Z in the connect portion  52  or connecting pipe  51 . 
     A float  61  of  FIGS. 4 to 6  has a spherical shape, but any shape, such as a cone shape, can be used. 
     The first regulating member  62  is a flat plate; however, as shown in  FIG. 7 , the first regulating member may have an inclined surface  62   b  wherein the undersurface of the flat plate inclines downwardly from an inner periphery of the through-hole to the outer surface of the flat plate member. When the molten metal surface of the melted metal is inclined greatly enough relative to the ladle to raise the float  61  in the delivery pipe  53 , this arrangement allows the outer surface of the float  61  to reliably adhere to the inner periphery of the through-hole  62   a , since the float  61  is guided to the through-hole  62   a  along the inclined surface  62   b  of the first regulating member  62 . As a result, the delivery pipe  53  can be completely blocked, and thus entry of the melted metal Z into the connect portion  52  or connecting pipe  51  can be reliably prevented. 
     In the embodiment of the invention, the pressurizing gas supplying means  50  includes the delivery pipe  53  ( FIG. 1 ); however, a discharging pipe  70  and a discharge hole protecting member  75  can be provided in place of the delivery pipe  53  ( FIG. 8 ). 
     The discharging pipe  70  includes a double circular tube  71  installed in the supplying means installing hole  25 . The double circular tube  71  serves as a discharge hole releasing a pressurizing gas into the storage space  11 . In the inner tube  72  and the outer tube  73  of the double circular tube  71 , long holes  72   a  and  73   a  passing through the inside and outside of the tube are disposed at four locations along the circumferential direction. These long holes  72   a  and  73   a  also serve as discharge holes for releasing a pressurizing gas to the storage space  11 . As shown in the cross-sectional view of  FIG. 9 , the long holes  72   a  and  73   a  each provided on the inner tube  72  and outer tube  73  are arranged in a single layer at regular intervals. The discharging pipe flange  74  is formed around the upper portion of the inner tube  72 , and the top portion of the outer tube  73  is fixed to the discharging pipe flange  74 . The discharging pipe flange  74  is structured to attach to the upper surface of the large lid  20  when the discharging pipe  70  is placed in the supplying means installing hole  25 . 
     A pressurizing gas guided to the connecting pipe  51  and the internal space  52   a  of the connect portion  52  is directed to the storage space  11  via one of the following three pathways: the lower portion of the inner tube  72  of the discharging pipe  70 ; the lower portion of the flow path between the inner wall of the outer tube  73  and the outer wall of the inner tube  72 ; or the long holes  72   a  and  73   a  each provided on the inner tube  72  and outer tube  73 . 
     The discharge hole protecting member  75  is located under the double circular tube  71 , and fixed to the outer surface of the outer tube  73  via a fixing member  76 . The discharge hole protecting member  75  inclines downward from the central part to the outside, and is almost in the shape of a straw hat. The member does not necessarily incline downwardly in a linear manner, but may incline downwardly in a curved manner, or the like. 
     Since the double circular tube  71  (discharge hole) is located above the discharge hole protecting member  75 , even if the melted metal Z splashes in the storage space  11  during transportation, the discharge hole protecting member  75  blocks the melted metal Z and prevents its adhesion to the discharge hole. As a result, clogging of the discharging pipe  70  caused by the solidified melted metal Z can be prevented, thereby reliably introducing a pressurizing gas into the storage space  11 . 
     Further, since the discharge hole protecting member  75  inclines downward from its central part to the outside, even if the melted metal Z splashes over the discharge hole protecting member  75 , the melted metal Z readily flows downward, preventing the collection of solidified melted metal on the member. 
     Since the long holes  72   a  and  73   a  are formed around the double circular tube, even if the lower portion of the discharging pipe  70  is clogged by solidified melted metal, inhibiting the introduction of the pressurizing gas into the storage space  11  via the aperture, the pressurizing gas can be guided to the storage space  11  via the long holes  72   a  and  73   a  formed on the inner tube  72  and outer tube  73 , thereby reliably pressurizing the inside of the storage space  11 . 
     Even if some of the long holes  72   a ,  73   a  are clogged by the splashed melted metal Z, the pressurizing gas can be supplied into the storage space  11  via other long holes  72   a  and  73   a.    
     Further, as shown in  FIG. 9 , since the long holes  72   a  and  73   a  disposed on the inner tube  75  and outer tube  76  are located on a single layer, even if the splashed melted metal Z passes through the long hole  73   a  on the outer tube  73  to the inner tube side  72 , adherence of the melted metal Z to the long hole  72   a  formed on the inner tube  72  can be prevented. Therefore, the long hole  72   a  on the inner tube  72  can avoid becoming clogged by the solidified melted metal Z. 
     In  FIG. 8 , the discharge hole protecting member  75  widens downward from the top to the outside; however, the member may also be in the form of a flat plate. 
     Further, in the present embodiment, the pressurizing gas supplying means  50  includes a delivery pipe  53  ( FIG. 1 ); however, as shown in  FIG. 10 , the means may be designed to accommodate a gas discharging portion  80  releasing a pressurizing gas to the storage space  11 , in place of the delivery pipe  53 . 
     The gas discharging portion  80  is a cylindrical member to be installed in the supplying means installing hole  25 , and is covered by a gas-permeable fireproof material  81 . A holding flange  82  is provided on the upper edge of the outer surface of the gas discharging portion  80 . The holding flange  82  is structured to attach to the upper surface of the large lid  20 , when the gas discharging portion  80  is installed in the supplying means installing hole  25 . A pressurizing gas guided to the connecting pipe  51  and the internal space  52   a  of the connect portion  52  permeates to the storage space  11  via the gas-permeable fire-resistant material  81  of the gas discharging portion  80 , thereby pressurizing the molten metal surface S of the melted metal Z. 
     Examples of the gas-permeable fire-resistant material  82  include an alumina, mullite (silica-alumina), silica, calcium silicate, and non-oxide-based porous sintered materials such as silicon carbide. 
     According to the arrangement above, even when a portion of the gas-permeable fire-resistant material  81  is clogged, the pressurizing gas can permeate through other parts of the material  81 , and can be reliably introduced into the storage space. Therefore, discharge failure of the melted metal Z can be prevented. 
     Because the storage space  11  is separated from the internal space  52   a  by the gas-permeable fire-resistant material  81 , even when the molten-metal surface S of the melted metal Z accommodated in the storage space  11  greatly inclines, the entry of the melted metal Z to the connect portion  52  and the connecting pipe  51  can be prevented. Therefore, it is possible to prevent the adherence of the solidified melted metal Z to the connect portion  52  and the connecting pipe inside  51 , which causes poor circulation of the pressurizing gas. 
     In an embodiment of the invention, the pressurizing gas supplying means  50  is removably set in the supplying means installing hole  25  via bolts ( FIG. 2 ); however, as shown in the partial enlarged cross-sectional view of  FIG. 12 , the pressurizing gas supplying means  50  may be removably set in the supplying means installing hole  25  using a supplying means installing device  90 . The supplying means installing device  90  includes an rotatable handle lever  91  to be held by an operator, and a pressurizing member  92  connected to the handle lever  91  via a linkage. The pressurizing gas supplying means  50  is detachably mounted to the supplying means installing hole  25  by applying or releasing the pressure on the supplying means, using the pressurizing member  92  along with the operation of the handle lever  91 . Examples of the supplying means installing device  90  include a toggle clamp, a cam clamp, etc. This structure enables the operator to easily lock or unlock the pressurizing gas supplying means  50  to the supplying means installing hole  25  by simply pulling the hand lever  91  down or up.  FIG. 12  shows that the connect portion  52  is integrally formed with the delivery pipe  53 , that a connecting pipe  51  is provided on the side of the connect portion  52 , and that the entire outer circumference of the connect portion  52  is in contact with the upper surface of the large lid  20  in the vicinity of the supplying means installing hole  25 . Further, sealing material such as packing can be used between the entire outer circumference of the connect portion  52  and the upper surface of the large lid  20  in the vicinity of the supplying means installing hole  25 . This reliably prevents pressurizing gas leakage from the space between the entire outer circumference of the connect portion  52  and the upper surface of the large lid  20 .