Patent Publication Number: US-6910521-B2

Title: Casting apparatus and molten metal feed apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a casting apparatus. 
   2. Description of the Related Art 
   In the field of die casting machines and other casting apparatuses, it is necessary to heat and melt metal from a solid state and feed the molten metal to the casting apparatus. As the method for heating and melting the metal, the technique of using induction heating to melt the metal and feeding that molten metal to the casting apparatus has been known. Induction heating is a method of heating metal for use for casting by inducing a current through the metal by electromagnetic induction and heating the metal by the Joule heat generated at that time. 
   On the other hand, a melted metal material is usually extremely high in temperature compared with the surroundings and is difficult to handle when feeding it to a casting apparatus. For example, with the method of scooping out melted metal material by a ladle to feed it to the casting machine, the metal material may solidify and oxidize. 
   As another method, for example, Japanese Unexamined Patent Publication (Kokai) No. 2001-239354 discloses a molten metal feed apparatus using induction heating to melt metal in a cylindrical furnace provided facing the cylinder of an injection apparatus and feeding that molten metal into a die casting machine. 
   The above molten metal feed apparatus is provided with an opening for ejecting the molten metal formed at the bottom of the cylindrical furnace into the cylinder and a lid for opening and closing the opening. By sliding the lid to open the opening, the molten metal in the cylindrical furnace flows into the cylinder by gravity. 
   This molten metal feed apparatus can feed the necessary amount of the molten metal into the injection apparatus without contact with air and can thereby maintain the quality of the molten metal. 
   With the molten metal feed apparatus disclosed in the above publication, however, there is a possibility of the molten metal in the furnace leaking out from the clearance formed between the opening and the lid closing that opening. If molten metal in the furnace leaks out, opening and closing of the lid will become difficult and the ladling quantity of the molten metal fed into the die casting machine may be dispersed. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a molten metal feed apparatus which can heat and melt the necessary amount of a metal material in a furnace to obtain molten metal and feed that molten metal into a casting apparatus by opening the furnace and which is free from leakage of the molten metal from the opening/closing part of the furnace. 
   Another object of the present invention is to provide a casting apparatus provided with the above molten metal feed apparatus. 
   According to a first aspect of the present invention, there is provided a molten metal feed apparatus for feeding molten metal to a casting apparatus provided with a holding vessel having an opening at its bottom and holding a metal material, a lid for closing the opening, a drive means for making the lid move with respect to the holding vessel to open or close the opening, and an induction heating coil for heating the metal material by induction of a current to the metal material in the holding vessel and generating a magnetic field applying to the molten metal a force preventing leakage of the molten metal in the holding vessel from between the opening and the lid. 
   According to a second aspect of the present invention, there is provided a casting apparatus having a molten metal feeding means for feeding a molten metal, the molten metal feeding means having a holding vessel having an opening at its bottom and holding a metal material, a lid for closing the opening, a drive means for making the lid move with respect to the holding vessel to open or close the opening, and an induction heating coil for heating the metal material by induction of a current to the metal material in the holding vessel and generating a magnetic field applying to the molten metal a force preventing leakage of the molten metal in the holding vessel from between the opening and the lid. 
   In the present invention, when an induction current flows through the molten metal in the holding vessel, an electromagnetic force acts on the molten metal due to the electromagnetic induction action between the induction current and the magnetic field from the induction heating coil. The opening at the bottom of the holding vessel is closed by the lid, but with just closing the opening by the lid, a clearance is formed between the opening and the lid and the molten metal may leak out by its own weight. The magnetic field generated by the induction heating coil heats the molten metal by induction. Further, the electromagnetic force acting on the molten metal in the holding vessel applies a force to the molten metal preventing leakage from between the opening and lid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein: 
       FIG. 1  is a sectional view of a molten metal feed apparatus according to an embodiment of the present invention; 
       FIG. 2  is a sectional view of the configuration of key parts of a die casting machine as an example of a casting apparatus according to the present invention; 
     FIG.  3 A and  FIG. 3B  are views of the structures of a holding vessel and induction heating coil; 
       FIG. 4  is a graph of the electromagnetic force acting on the molten metal by the electromagnetic induction action between the induction current flowing through the molten metal ML and the magnetic field generated by the induction heating coil and the liquid pressure of the molten metal; 
       FIG. 5  is a sectional view of an example of the state of molten metal in the holding vessel in the case of arranging an induction heating coil with a fixed diameter at the entire region at the outside of the holding vessel along the center axis without considering the shape of the induction heating coil; 
       FIG. 6  is a graph of the electromagnetic force acting on the molten metal and the liquid pressure of the molten metal in the case of the induction heating coil shown in  FIG. 5 ; 
     FIG.  7 A and  FIG. 7B  are sectional views of another example of an induction heating coil according to an embodiment of the present invention; 
     FIG.  8 A and  FIG. 8B  are views of another type of the holding vessel according to an embodiment of the present invention; 
       FIG. 9  is a sectional view of the state of allowing molten metal to fall by its own weight from the opening IS of the holding vessel and be fed into the sleeve; 
       FIG. 10  is a view of the configuration of a molten metal feed apparatus according to a second embodiment of the present invention; 
       FIG. 11  is a view of the configuration of a molten metal feed apparatus according to a third embodiment of the present invention; 
       FIG. 12  is a view of the state before insertion of an ingot into the holding vessel in a molten metal feed apparatus; 
       FIG. 13  is a view for explaining a procedure for feeding molten metal into a sleeve in a molten metal feed apparatus; 
       FIG. 14  is a view of the configuration of a molten metal feed apparatus according to a fourth embodiment of the present invention; 
       FIG. 15  is a view of a molten metal feed apparatus having another opening/closing mechanism; 
       FIG. 16  is a view of a molten metal feed apparatus having still another opening/closing mechanism; 
       FIG. 17  is a view of a molten metal feed apparatus having still another opening/closing mechanism; and 
       FIG. 18  is a sectional view of the configuration of a molten metal feed apparatus according to a fifth embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail below while referring to the attached figures. 
   First Embodiment 
     FIG. 1  is a sectional view of a molten metal feed apparatus according to an embodiment of the present invention. 
   The molten metal feed apparatus  1  shown in  FIG. 1  has a melting heater  2  and a material feed mechanism  51 . 
   The material feed mechanism  51  has a hopper  55 , a cylinder  52 , and a screw  53 . 
   The hopper  55  has a conical shape and can hold a metal material M inside it. The hopper  55  has a feeder  55   a  communicating with the inside of the cylinder  52  at its bottom end. 
   The metal material M fed into the hopper  55  is fed into the cylinder  52  through the feeder  55   a  by its own weight. 
   The metal material M stored in the hopper  55  is for example comprised of aluminum alloy or another metal in a spherical or elongated granular shape. 
   The cylinder  52  is comprised of a tubular member and is formed at part of its outside with a port  52   a  communicating with the feeder  55   a  of the hopper  55 . 
   The front end side of the cylinder  52  is connected to the top end of the later explained holding vessel  3 . The inside of the cylinder  52  and the inside of the holding vessel  3  are communicated with each other by this. 
   The screw  53  is provided rotatably inside the cylinder  52 . One end of the screw  53  is connected with an output shaft  54   a  of a motor  54  affixed to one end of the cylinder  52 . 
   When the screw  53  is made to turn in a predetermined direction by the rotation of the motor  54 , the metal material M fed from the hopper  55  to the inside of the cylinder  52  is transported in the direction of the arrow J shown in FIG.  1  and drops from the front end of the cylinder  52  to the inside of the holding vessel  3 . The amount of the metal material M transported to the holding vessel  3  (amount fed) is determined in accordance with the amount of rotation of the screw  53 . 
   The melting heater  2  has the holding vessel  3  arranged above a gate  70   h  of the sleeve  70  of the later explained die casting machine, an induction heating coil  10  arranged around the holding vessel  3 , and an opening/closing mechanism  21 . 
   The opening/closing mechanism  21  has a lid  22  and a cylinder apparatus  23 . 
   The lid  22  is a plate-shaped member able to close the opening  3   d  of the bottom (bottom end) of the holding vessel  3  by being moved to face the opening  3   d.    
   This cylinder apparatus  23  is provided with a piston rod  24  linked at its front end to the lid  22 . This piston rod  24  extends or contracts in the directions of the arrows D 1  and D 2  by for example compressed air or hydraulic power. By the piston rod  24  sliding in the directions D 1  and D 2 , the opening  3   d  of the bottom end of the holding vessel  3  is opened/closed by the lid  22 . 
     FIG. 2  is a sectional view of the configuration of key parts of a die casting machine as an example of a casting apparatus. 
   As shown in  FIG. 2 , the die casting machine  60  has a fixed die  90 , a movable die  80  provided to be able to be opened and closed with respect to the fixed die, a sleeve  70  comprised of a tubular member provided at the fixed mold  90 , and a plunger tip  72  fixed to the front end of a plunger rod  73  and fitting into the inner circumference of the sleeve  70 . 
   The sleeve  70  is communicated with a cavity Ca formed between the clamped fixed die  90  and movable die  80 . 
   In the state with the fixed die  90  and movable die  80  clamped by a not shown clamping mechanism, a predetermined amount of molten metal (metal material) ML is fed into the sleeve  70  through the gate  70   h  of the sleeve  70 . 
   Next, the molten metal ML in the sleeve  70  is injected into the cavity Ca formed between the fixed die  90  and the movable die  80  by the action of the plunger tip  72 . 
   After the molten metal ML filled in the cavity Ca solidifies, the movable die  80  is opened and the casting in the cavity Ca is ejected by ejection pins  91  provided at the movable die  80 . 
   FIG.  3 A and  FIG. 3B  are views of the structures of the holding vessel  3  and induction heating coil  10 , wherein  FIG. 3A  is a top view of the holding vessel  3  and  FIG. 3B  is a sectional view along the line A—A shown in FIG.  3 A. 
   As shown in FIG.  3 A and  FIG. 3B , the holding vessel  3  is comprised of a tubular member having a holding space  3   a  able to hold the metal material M. The holding vessel  3  is formed by a material such as austenitic stainless steel, copper, copper alloy, or another nonferromagnetic metal, or electrically insulating ceramic or another insulator material. Note that these materials are made nonferromagnetic. The reason for using such nonferromagnetic materials is to prevent magnetic flux from concentrating at the holding vessel  3  at the time of induction heating or to cause a larger electromagnetic force to act on the metal material M held in the holding vessel  3  by the induction heating coil  10 . 
   The opening  3   d  at the bottom end of the holding vessel  3 , as shown in  FIG. 3B , is closed by the lid  22 . At this time, the abutting face  22   s  of the lid  22  facing the bottom end face  3   e  of the holding vessel  3  is arranged to contact the bottom end face  3   e , but a clearance may form between the bottom end face  3   e  and abutting face  22   s.    
   The induction heating coil  10  is arranged around the holding vessel  3  concentrically with the center axis O of the holding vessel  3 . 
   The bottom end side of the induction heating coil  10  along the center axis O is positioned near the contact position of the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22 . 
   Further, the diameter d1 of the top end side of the induction heating coil  10  along the center axis O is the maximum diameter, while the diameter d 2  of the bottom end side is the minimum one. The diameter of the induction heating coil  10  gradually becomes smaller from the top end to the bottom end. 
   The induction heating coil  10  is for example supplied with tens of kHz or so of high frequency current. When the induction heating coil  10  is supplied with high frequency current, a magnetic field is generated. This magnetic field induces a current in the metal material M in the holding vessel  3 . If current flows through the metal material M, Joule heat results in the metal material heating up and melting. Due to this, the metal material M becomes the molten metal ML. 
   After the metal material M becomes the molten metal ML, the electromagnetic induction action between the induction current flowing through the molten metal ML and the magnetic field generated at the induction heating coil  10  cause an electromagnetic force to act on the molten metal ML. This electromagnetic force is mainly a force directed toward the center of the holding vessel  3 . 
   Here, the force acting on the molten metal ML melted by the induction heating coil  10  of the above shape will be explained referring to FIG.  4 . 
     FIG. 4  is a graph of the electromagnetic force F acting on the molten metal ML by the electromagnetic induction action between the induction current flowing through the molten metal ML and the magnetic field generated by the induction heating coil  10  and the liquid pressure P of the molten metal ML. 
   If the contact position of the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22  is made the reference height h 0 , the liquid pressure acting on the now liquid molten metal ML of the holding vessel  3  becomes the maximum at the reference height ho and becomes smaller toward the top side of the holding vessel  3 . 
   On the other hand, since the induction heating coil  10  has the above shape, the magnetic flux of the magnetic field generated at the inner circumference of the induction heating coil  10  becomes maximum at the bottom end side of the induction heating coil  10  and falls toward the top end side. 
   Therefore, the electromagnetic force F acting on the molten metal ML in the center axis direction of the holding vessel  3  due to the induction heating coil  10  becomes maximum near the reference height h 0  due to the shape of the induction heating coil  10  and becomes smaller toward the top side of the holding vessel  3 . 
   Accordingly, the molten metal M of the holding vessel  3  becomes the shape such as shown in FIG.  3 B. 
   The shape of the molten metal ML shown in  FIG. 3B  becomes close to a cylindrical shape with a diameter substantially equal from the bottom end to the top end. At the bottom end side of the holding vessel  3 , the inner circumferential surface of the holding vessel  3  and the molten metal ML are separated from each other. 
   That is, the molten metal ML in the holding vessel  3  is acted upon by a force keeping the height relatively low and preventing leakage from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22 . 
   Therefore, it is possible to prevent the molten metal ML from leaking out by its own weight from the holding vessel  3  in the state with the lid  22  closing the opening  3   d.    
   Here,  FIG. 5  is a sectional view of an example of the state of molten metal ML in the holding vessel  3  in the case of arranging an induction heating coil  300  with a fixed diameter d at the entire region at the outside of the holding vessel  3  along the center axis O without considering the shape of the induction heating coil. 
   As shown in  FIG. 5 , if the diameter d of the induction heating coil  300  is substantially constant, the electromagnetic force F acting on the molten metal ML in the center axis direction of the holding vessel  3  becomes a substantially constant value along the center axis direction as shown for example in FIG.  6 . 
   On the other hand, the liquid pressure P acting on the then liquid molten metal ML of the holding vessel  3  becomes maximum at the reference height h 0  and becomes smaller toward the top side of the holding vessel  3 . 
   Therefore, from the relationship between the electromagnetic force F and the liquid pressure P, the molten metal ML ends up shaped as shown in  FIG. 5  with a high height and flaring sides and the molten metal ML may leak out from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22 . It is therefore necessary to generate a stronger electromagnetic force to prevent this. 
   As explained above, by forming the induction heating coil  10  into a suitable shape, it is possible to prevent the molten metal ML from leaking by its own weight from the holding vessel  3  in the state with the lid  22  closing the opening  3   d  by a relatively small electromagnetic force. Further, by suitably selecting not only the shape of the induction heating coil  10 , but also the shape of the induction heating coil  10  and the arrangement of the induction heating coil  10  with respect to the holding vessel  3  or just the arrangement of the induction heating coil  10  with respect to the holding vessel  3 , it is possible to prevent the molten metal ML from leaking by its own weight from the holding vessel  3  in the state with the lid  22  closing the opening  3   d.    
   Note that to determine the shape or arrangement of the induction heating coil  10 , it is necessary to consider the relationships among the intensity of the magnetic field generated by the induction heating coil  10 , the amount of the metal material M fed into the holding vessel  3 , the height H of the induction heating coil  10  along the center axis O, etc. 
   Here, another example of an induction heating coil capable of preventing leakage of the molten metal ML from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22  will be explained with reference to FIG.  7 A and FIG.  7 B. 
   The induction heating coil  10 A shown in  FIG. 7A  is arranged at the outer circumference of the holding vessel  3  in the same way as the above induction heating coil  10 . Further, the induction heating coil  10 A is formed substantially equal in diameter d from the top end to the bottom end. The bottom end of the induction heating coil  10 A is arranged near the position where the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid abut. 
   The height H of the induction heating coil  10 A in the direction along its center axis O is limited to a predetermined value so that the electromagnetic force acts only below the molten metal ML in the holding vessel  3 . That is, the induction heating coil  10 A is arranged so that the electromagnetic force directed toward the center axis O concentrates and acts only at the bottom region of the molten metal ML in the holding vessel  3  relative to the amount of molten metal ML in the holding vessel  3 . Due to this, the height of the molten metal ML is suppressed and the liquid pressure of the bottom region becomes lower and balanced with the relatively low electromagnetic force. 
   By restricting the height H of the induction heating coil  10 A relative to the amount of the molten metal ML in the holding vessel  3 , as shown in  FIG. 7A , when the inner circumferential surface of the holding vessel  3  and the molten metal ML separate at the bottom end side of the holding vessel  3 , it becomes possible to prevent leakage of the molten metal ML from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22 . 
   The induction heating coil  10 B shown in  FIG. 7B  has a shape and arrangement similar to the induction heating coil  10 A shown in  FIG. 7A , but the bottom end of the induction heating coil  10 B is arranged further lower from the bottom end face  3   e  of the holding vessel  3 . 
   By arranging the bottom end of the induction heating coil  10 B further lower than the bottom end face  3   e  of the holding vessel  3  in this way, it is possible to increase the electromagnetic force directed to the center axis O at the position of the bottom end of the holding vessel  3  compared with the induction heating coil  10 A. As a result, compared with the induction heating coil  10 A, it becomes possible to prevent more reliably the leakage of the molten metal ML from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22 . 
   FIG.  8 A and  FIG. 8B  are views of another type of the holding vessel  3 , where  FIG. 8A  is a front view and  FIG. 8B  is a sectional view along the line C—C in FIG.  8 A. 
   When the holding vessel  3  is formed by a ferromagnetic material such as iron, an eddy current is generated in the circumferential direction of the holding vessel  3  by the magnetic field generated by the induction heating coil  10  and the possibility arises of the holding vessel  3  being heated. 
   Therefore, the holding vessel  3 A shown in FIG.  8 A and  FIG. 8B  is formed with a notch  3   k  at part of its surface along the center axis O. By forming this notch  3   k , the path of current in the circumferential direction of the holding vessel  3 A caused at the time of induction heating is cut and the holding vessel  3 A can be prevented from heating up. 
   Further, the notch  3   k  is for example filled with a ceramic or other insulating member Is. By this, it is possible to prevent the atmosphere from invading the holding vessel  3 A and possible to keep the inside of the holding vessel  3 A a nonoxidizing atmosphere. Note that when there is no problem even if the atmosphere invades the inside of the holding vessel  3 A, the insulating member Is need not be provided. 
   As another method for preventing heating of the holding vessel  3 , it may be considered to adjust the thickness TH of the holding vessel  3  shown in FIG.  3 A. 
   The depth of penetration δ of the eddy current generated at the holding vessel  3  can be found from a predetermined formula from the resistance ρ (Ω·m) of the holding vessel  3 , the magnetic permeability μ of the holding vessel  3 , and the frequency f (Hz) of the current applied to the induction heating coil  10 . 
   By making the thickness TH of the holding vessel  3  smaller than the depth of penetration δ of the eddy current, it is possible to prevent heating of the holding vessel  3 . 
   In the molten metal feed apparatus  1  of the above configuration, if heating and melting the metal material M in the holding vessel  3  and sliding the lid  22  in the direction D 1  as shown in  FIG. 9  after reaching a predetermined temperature, the molten metal ML will drop out from the opening  3   d  of the holding vessel  3   d  by its own weight and be fed to the sleeve  70  of the die casting machine through the gate  70   h.    
   As explained above, according to the present embodiment, when heating and melting the metal material M in the holding vessel  3  by induction heating to obtain the molten metal ML, by determining the shape and/or arrangement of the induction heating coil  10  to heat the metal material M by induction heating and enable generation of a magnetic field causing a force for preventing leakage of the molten metal ML from between the bottom end face  3   e  of the holding vessel  3  and the abutting face  22   s  of the lid  22  to act on the molten metal, it is possible to prevent leakage of the molten metal ML without any alteration in the opening/closing mechanism  21  of the holding vessel  3 . 
   Note that in the above embodiment, the explanation was given while mentioning several types of the induction heating coil  10 , but the present invention is not limited to these coils. It is also possible to combine the above types and possible to employ other types. 
   Second Embodiment 
     FIG. 10  is a view of the configuration of a molten metal feed apparatus according to a second embodiment of the present invention. Note that in  FIG. 10 , components the same as in the molten metal feed apparatus  1  of the first embodiment are assigned the same reference numerals. 
   In the first embodiment, the explanation was given with reference to an example of the material feed mechanism  51  for feeding a metal material in the solid state as the metal material feeding means of the present invention, but in the molten metal feed apparatus  200  according to this embodiment, the holding vessel  3  is fed not a metal material in a solid state, but a metal material in a liquid state, that is, the molten metal ML. The rest of the configuration is exactly the same as in the first embodiment explained above. 
   In  FIG. 10 , the melting furnace  401  holds molten metal ML obtained by melting for example aluminum. 
   Normally, with the melting furnace  401 , the aluminum can only be raised in temperature to about 750° C. Sometimes, however, it is desired to feed aluminum into a die casting machine at the state of an extremely high temperature of about 800° C. 
   In this case, a predetermined amount of the molten metal ML of aluminum in the melting furnace  401  is scooped up by a ladle  400  held by a not shown conveyance mechanism and conveyed to the holding vessel  3 . 
   In the holding vessel  3 , in the same way as in the above embodiment, the melt of the molten metal ML of aluminum is heated by induction heating to raise it in temperature. 
   By configuring the present embodiment in this way, it becomes possible to raise the temperature of the molten metal ML to one not possible in a melting furnace  401  and feed it to a die casting machine or other casting apparatus. 
   Note that the molten metal feed apparatus  200  according to the present embodiment can make use of the various modifications of the holding vessel  3  and induction heating coil  10  explained above. 
   Third Embodiment 
     FIG. 11  is a view of the configuration of a molten metal feed apparatus according to a third embodiment of the present invention. Note that in  FIG. 11 , components the same as the molten metal feed apparatus  1  according to the first embodiment are assigned the same reference numerals. 
   In the first and second embodiments, the case of feeding a granular state metal material or molten metal into the holding vessel  3  was explained, but in the present embodiment, the case of feeding metal in a solid state such as an ingot or billet into the holding vessel  3  will be explained. 
   The molten metal feed apparatus  301  shown in  FIG. 11  has an opening/closing mechanism  21 B. This opening/closing mechanism  21 B has a lid  22 B and an elevating cylinder  25  for raising and lowering the lid  22 B in the vertical directions shown by the arrows E 1  and E 2 . 
   The lid  22 B is linked with the piston rod  26  of the elevating cylinder  25  and can pivot in the direction of the arrows R 1  and R 2  about the axis  27  with respect to the piston rod  26  by an actuator  30 . 
     FIG. 12  is a view of the state before insertion of an ingot IG in the holding vessel  3  in the molten metal feed apparatus  301 . 
   The lid  22 B is lowered in the direction of the arrow E 2  and the ingot IG is placed on the lid  22 B held in a horizontal state. 
   When the lid  22 B is raised in the direction of the arrow E 1  from this state, as shown in  FIG. 11 , the lid  22 B abuts against the bottom end face  3   e  of the holding vessel  3 , whereby the opening  3   d  of the holding vessel  3  is closed. 
   In the state shown in  FIG. 11 , induction heating is used to heat and melt the ingot IG, then, as shown in  FIG. 13 , the lid  22 B is made to pivot in the direction of the arrow R 1  to open the opening  3   d  of the furnace  3  and thereby feed molten metal ML inside the sleeve  70 . 
   In this way, in the molten metal feed apparatus  301  of the present embodiment, the opening/closing mechanism  21 B opens and closes the opening  3   d  of the holding vessel  3  and performs the role of the metal material feeding means for feeding the ingot IG inside the holding vessel  3 . 
   According to the molten metal feed apparatus  301  of the present embodiment, a mass of metal material such as an ingot is fed into the holding vessel  3 , so the oxidation of the metal material can be suppressed so that the quality of the molten metal can be improved. Further, it becomes possible to make the volume of the metal material smaller. 
   Note that the molten metal feed apparatus  301  according to the present embodiment can make use of the various modifications of the holding vessel  3  and induction heating coil  10  explained above. 
   Fourth Embodiment 
     FIG. 14  to  FIG. 17  are views of the configuration of a molten metal feed apparatus according to a fourth embodiment of the present invention. 
   In the above embodiments, the explanation was made of a technique for preventing the molten metal ML in the holding vessel  3  from leaking from any clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  3 . 
   When melting a metal material by induction heating in the holding vessel  3 , however, from the viewpoint of suppression of oxidation of the metal, it is desirable to make the atmosphere in the holding vessel  3  an inert gas. 
   The larger the clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  2 , however, the longer the time required for replacement of the atmosphere and the greater the amount of inert gas required. 
   Further, if the clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  3  is large, if the induction heating stops due to a blackout or other reason while melting the metal material in the holding vessel  3  due to the induction heating, the molten metal may leak out from the clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  3 . 
   Therefore, it is desirable to make the clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  3  as small as possible. 
   In the present embodiment, a configuration enabling the clearance formed between the lid  22  and the bottom end face  3   e  of the holding vessel  3  to be reduced will be explained. 
   The molten metal feed apparatus  500  shown in  FIG. 14  differs from the molten metal feed apparatus  1  according to the first embodiment explained above only in the opening/closing mechanism  21 C. The rest of the configuration is the same. 
   In  FIG. 14 , the opening/closing mechanism  21 C has a lid  22 C and an actuator  30  for pivoting the lid  22 C about a shaft  27 . 
   The actuator  30  is for example configured by an electric motor and a transmission mechanism. 
   If driving the actuator  30  to make the lid  22 C pivot in the direction of the arrow R 2 , the abutting face  22 Cs of the lid  22 C abuts against the bottom end face  3   e  of the holding vessel  3 . 
   By maintaining a fixed output of the actuator  30  in the state with the abutting face  22 Cs of the lid  22 C abutting against the bottom end face  3   e  of the holding vessel  3  so as to press the abutting face  22 Cs of the lid  22 C against the bottom end face  3   e  of the holding vessel  3  by a predetermined force f, it is possible to reduce the clearance formed between the abutting face  22 Cs and the bottom end face  3   e.    
     FIG. 15  is a view of a molten metal feed apparatus having an opening/closing mechanism of another configuration. Note that the molten metal feed apparatus  501  shown in  FIG. 15  is the same in configuration as the molten metal feed apparatus  500  shown in  FIG. 14  except for the opening/closing mechanism. Further, components the same as the molten metal feed apparatus  500  shown in  FIG. 14  are assigned the same reference numerals. 
   The opening/closing mechanism  21 D shown in  FIG. 15  has a lid  22 D, an actuator  30  for making the lid  22 D pivot about the shaft  27 , a wedge member  32 , a cylinder apparatus  29 , and a guide member  31 . 
   The lid  22 D is provided at the opposite side to the abutting face  22 Ds with an inclined face  22 Da inclined by a predetermined angle with respect to the abutting face  22 Ds. 
   The wedge member  32  is movably supported by the guide member  31  in the horizontal direction shown by the arrows D 1  and D 2 . This wedge member  32  is provided with an inclined face  32   a  inclined relative to the inclined face  22 Da of the lid  22 D by the same angle as the inclined face  22 Da at the surface opposite to the surface supported by the guide member  31 . 
   The guide member  31 , while not shown, is arranged parallel at the two sides below the holding vessel  3  so as not to obstruct the path of feed of the molten metal ML ejected from the opening  3   d  of the holding vessel  3  to the sleeve  70 . 
   The cylinder apparatus  29  is provided with a piston rod  28  extending and contracting in the directions of the arrows D 1  and D 2 . The front end of the piston rod  28  is linked with the wedge member  32 . The cylinder apparatus  29  moves the wedge member  32  in the directions of the arrows D 1  and D 2  by extension and contraction of the piston rod  28  in the directions of the arrows D 1  and D 2 . 
   If driving the actuator  30  to make the lid  22 D pivot in the direction of the arrow R 2 , the abutting face  22 Ds of the lid  22 D abuts against the bottom end face  3   e  of the holding vessel  3 . 
   If making the wedge member  32  move in the direction of the arrow D 1  from this state, the inclined face  32   a  of the wedge member  32  and the inclined face  22 Da of the lid  22 D will strike each other. Further, the wedge member  32  will be made to advance in the direction of the arrow D 1  and the wedge member  32  will be pressed by a force f 2 . 
   The force f 2  pressing the wedge member  32  is converted to the force f 3  pressing the lid  22 D toward the bottom end face  3   e  of the holding vessel  3 . At this time, the force f 3  is amplified by the force f 2  by the wedge effect. 
   Due to this, it is possible to press the lid  22 D toward the bottom end face  3   e  of the holding vessel  3  by a large force and possible to reduce the clearance formed between the abutting face  22 Ds and the bottom end face  3   e . That is, in the configuration of the opening/closing mechanism shown in  FIG. 14 , it is necessary to have the actuator  30  generate a large force, but in this example, it is possible to convert the output of the cylinder apparatus  29  to a large force by the wedge effect, so it is not necessary to have the actuator  30  generate a large force. 
     FIG. 16  is a view of a molten metal feed apparatus having still another opening/closing mechanism. Note that the molten metal feed apparatus  502  shown in  FIG. 16  is the same in configuration as the molten metal feed apparatus  500  shown in  FIG. 14  except for the opening/closing mechanism. 
   The opening/closing mechanism  21 E shown in  FIG. 16  has a lid  22 E, a cylinder apparatus  23 , and a guide member  35 . 
   The lid  22 E is supported by the guide member  35  movably in the horizontal direction shown by the arrows D 1  and D 2 . 
   The abutting face  22 Es of the lid  22 E does not perpendicularly intersect the center axis O of the holding vessel  3 , but is inclined with respect to the plane perpendicularly intersecting the center axis O by a predetermined angle. 
   On the other hand, the bottom end face  3   e  of the holding vessel  3  does not perpendicularly intersect the center axis O of the holding vessel  3 , but is inclined with respect to the plane perpendicularly intersecting the center axis O by a predetermined angle. 
   The cylinder apparatus  23  makes the lid  22  move in the directions of the arrows D 1  and D 2  by extension and contraction of the piston rod  24  in the directions of the arrows D 1  and D 2 . 
   The guide member  35 , while not shown, is arranged parallel at the two sides below the holding vessel  3  so as not to obstruct the path of feed of the molten metal ML ejected from the opening  3   d  of the holding vessel  3  to the sleeve  70 . 
   If using the cylinder apparatus  23  to make the lid  22 E move in the direction of the arrow D 2 , the abutting face  22 Es of the lid  22 E will abut against the bottom end face  3   e  of the holding vessel  3 , whereby the opening  3   d  of the holding vessel  3  will be closed by the lid  22 E. 
   If further pressing the lid  22 E in the direction of the arrow D 2  by the force f 2  in this state, due to the wedge effect between the bottom end face  3   e  and the abutting face  22 Es, the force f 2  is converted to a force f 3  pressing the lid  22 E against the bottom end face  3   e  of the holding vessel  3 . Due to this, it is possible to press the lid  22 E against the bottom end face  3   e  of the holding vessel  3  by a large force and possible to reduce the clearance formed between the abutting face  22 Es and the bottom end face  3   e.    
   In this example, the drive force of the actuator for opening and closing the lid  22 E with respect to the opening  3   d  of the holding vessel, that is, the cylinder apparatus  23 , is utilized to reduce the clearance formed between the abutting face  22 Es and the bottom end face  3   e , so it is not necessary to provide a separate actuator for pressing the lid  22 E against the holding vessel  3 . 
     FIG. 17  is a view of a molten metal feed apparatus having still another opening/closing mechanism. Note that the molten metal feed apparatus  503  shown in  FIG. 17  is the same in configuration as the molten metal feed apparatus  500  shown in  FIG. 14  except for the opening/closing mechanism. 
   The opening/closing mechanism  21 F shown in  FIG. 17  is provided with a lid  22 F and a cylinder apparatus  38 . 
   The cylinder apparatus  38  is provided with a piston rod  39  extending and contracting in the directions of the arrows G 1  and G 2 . The front end of the piston rod  39  is fixed to the lid  22 F. 
   The directions G 1  and G 2  of extension and contraction of the piston rod  39  are not parallel to the bottom end face  3   e  of the holding vessel  3 , but are inclined by a predetermined angle θ with respect to the bottom end face  3   e.    
   The lid  22 F is fixed to the piston rod  39  so that the abutting face  22 Fs becomes parallel to the bottom end face  3   e  of the holding vessel  3 . 
   If extending the piston rod  39  to make the abutting face  22 Fs of the lid  22 F abut against the bottom end face  3   e  of the holding vessel  3  and press the abutting face  22 Fs against the bottom end face  3   e , due to the wedge effect, the lid  22 F is pressed against the bottom end face  3   e  of the holding vessel  3  by a larger force than the output of the cylinder apparatus  38 . 
   Note that the molten metal feed apparatuses  500  to  503  shown in  FIG. 14  to  FIG. 17  were explained with reference to the case of provision of the material feed mechanism  15  as a metal material feeding means, but it is also possible to use the metal material feeding means explained in the second embodiment for the molten metal feed apparatuses  500  to  503 . 
   Further, the molten metal feed apparatuses  500  to  503  according to the present embodiment can make use of the various modifications of the holding vessel  3  and induction heating coil  10  explained above. 
   Fifth Embodiment 
     FIG. 18  is a sectional view of the configuration of a molten metal feed apparatus according to a fifth embodiment of the present invention. Note that in  FIG. 18 , components the same as in the above components are assigned the same reference numerals. Further, the configurations of the holding vessel  3  and induction heating coil  10  are similar to those of the above embodiments. 
   In the molten metal feed apparatus according to the above embodiments, the magnetic flux generated by the induction heating coil  10  passes through the lid  22 . When the material forming the lid  22  is iron or another ferromagnetic material, passage of magnetic flux results in an eddy current in the lid  22 , whereby the lid  22  is heated. That is, part of the energy used for the induction heating is used for heating the lid  22 , so an energy loss occurs. 
   Further, if the lid  22  continues being heated by the eddy current, the temperature of the lid  22  will rise too much and damage may occur. 
   In the present embodiment, a configuration enabling the energy loss due to the lid  22  to be prevented and heating of the lid  22  to be stopped will be explained. 
   In  FIG. 18 , the opening/closing mechanism  21 G has a contact member  601 , an elastic member  602 , a flange member  603 , a tubular member  604 , and an actuator  610 . 
   The contact member  601 , elastic member  602 , flange member  603 , and tubular member  604  form the lid of the present invention. 
   The actuator  610  pivots the holding member  605  in the directions of the arrows R 1  and R 2 . 
   The contact member  601  is a disk-shaped member arranged at a position coming into direct contact with the molten metal ML in the holding vessel  3 . The outer circumferential surface of the contact member  601  forms a taper face  601   t  inclined at a predetermined angle. 
   The tubular member  604  is comprised of a cylindrically shaped member. The inner circumferential surface at the top end side forms a taper face  604   t  for supporting the taper face  601   t  of the contact member  601 . The tubular member  604  fits at its outer circumference into a circular hole  605   a  formed in the holding member  605 . 
   The flange member  603  is provided with a projection  603   a  to be inserted into the inner circumference of the tubular member  604 . The outer circumference is fastened to the holding member  605  by bolts  608 . The top face of the projection  603   a  of the flange member  603  becomes the support face  603   b  supporting the bottom face side of the contact member  601  through the elastic member  602 . 
   The elastic member  602  is comprised of a disk-shaped member and is sandwiched between the bottom face of the contact member  601  and the support face  603   b  of the flange member  603 . The elastic member  602  is formed by a material elastically deformable when acted on by a compression force from the bottom face of the contact member  601  and the support face  603   b  of the flange member  603 . Specifically, it is formed by bulk fiber paper etc. 
   The holding member  605  is formed, at the outer circumference of the circular hole  605   a  into which the tubular member  604  is fit, with a not shown notch so as to cut the path of the induction current arising due to the magnetic field occurring in the induction heating coil  10 . 
   In the present embodiment, to prevent heating of the lid due to the eddy current at the time of induction heating, the lid is formed not from a ferromagnetic material such as iron, but from a metal not a ferromagnetic material such as austenitic stainless steel or copper or an insulator such as a ceramic (these being referred to as “nonferromagnetic materials”). 
   Specifically, the material forming the holding member  605  is made for example copper and the materials forming the contact member  601 , flange member  603 , and tubular member  604  are made for example ceramic materials. 
   Further, the contact member  601  comes directly into contact with the molten metal ML, so a large amount of heat is conducted in a short time. Therefore, the contact member  601  is formed by a material stable at a high temperature and tough against thermal shock. Specifically, for example, silicon nitride (Si 3 N 4 ), silicon aluminum oxynitride (Si 3 N 4 —Al 2 O 3 ), boronitride (BN), aluminum titanate (TiO 2 —Al 2 O 3 ), or another ceramic material may be mentioned. 
   Further, the contact member  601  can be damaged by the heat stress if the temperature difference becomes large inside the contact member  601 , so it is preferable to reduce the heat capacity of the contact member  601  as much as possible. Therefore, the contact member  601  is made a plate shape and its thickness is determined considering the heat conductivity and the toughness with respect to the internal stress due to heat of the material forming the contact member  601 . Specifically, when melting aluminum, magnesium, or other metal and using a ceramic material for the material forming the contact member  601 , considering the fact that the melting temperature of aluminum or magnesium is about 700° C., the thickness of the contact member  601  is preferably about 3 to 8 mm. If a thickness over this, a large temperature difference will arise between the surface of the contact member  601  at the side contacting the molten metal ML and the surface at the opposite side, cracks will occur in the direction along the surface of the contact member  601 , and use will become impossible. Further, if too thin, the member will easily break. Therefore, the thickness is preferably made at least 3 mm. 
   In the molten metal feed apparatus  600  of the above configuration, if melting the metal material by induction heating inside the holding vessel  3 , the contact member  601  becomes extremely high in temperature due to direct contact with the molten metal ML and expands to the heat. 
   The heat expansion of the contact member  601  in the radial direction is absorbed by the contact member  601  moving downward due to the interaction between the taper face  601   t  of the contact member  601  and the taper face  604   t  of the tubular member  604  and striking the elastic member  602 . 
   The heat expansion of the contact member  601  in the thickness direction is absorbed by the contact member  601  pressing against the elastic member  602  as it is. 
   Therefore, the contact member  601  is resistant to damage by heat stress. 
   As explained above, according to the molten metal feed apparatus  600  of the present embodiment, by suitably selecting the material of the lid not requiring heating, it is possible to suppress energy loss at the time of induction heating, possible to suppress heating of the lid, and possible to extend the life of the lid. 
   Further, by configuring the lid by a plurality of members, in particularly by configuring the portion coming into direct contact with the molten metal ML by the contact member  601  and adopting a structure able to absorb the heat expansion of the contact member  601 , it becomes possible to greatly extend the life of the most likely to break contact member  601 . 
   Note that in the present embodiment, the holding vessel  3 , the contact member  601 , the tubular member  604 , the flange member  603 , and the elastic member  602  were made circular in sectional shape in the horizontal direction, but the sectional shape of these members in the horizontal direction may be made any shape (for example, squares) and gradients may be given to the surfaces where the contact member  601  and tubular member  604  contact each other. 
   Further, in the present embodiment, an elastic member  602  was used for absorbing the heat expansion of the contact member  601 . When using a ceramic material for the contact member  601 , however, the heat expansion rate is not that large, so it is also possible not to use an elastic member  602  and to select a material able to absorb the expansion of the contact member  601  for the ceramic material used as the material forming the flange member  603 . 
   Further, the molten metal feed apparatus  600  according to the present embodiment was not provided with a metal material feeding means for feeding the metal material to the holding vessel, but the molten metal feed apparatus  600  may also be made a molten metal feed apparatus using a metal material feeding means as explained in the first to third embodiments. 
   Further, the molten metal feed apparatus  600  according to the present embodiment can make use of the various modifications of the holding vessel  3  and induction heating coil  10  explained above. 
   Further, it is possible to press the lid of the molten metal feed apparatus  600  according to the present embodiment against the bottom end face of the holding vessel  3  by applying the technique explained with reference to the fourth embodiment. 
   While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. 
   In the above embodiments, the explanation was given with reference to an example of a die casting machine as a casting apparatus fed the molten metal from the molten metal feed apparatus of the present invention, but the invention is not limited to this. For example, it can also be applied to a casting apparatus using sand casting or gravity die casting or another casting method. 
   Further, the molten metal feed apparatuses of the above embodiments were explained with reference to the case of the metal material to be melted being mainly aluminum, but it is also possible to heat and melt high melting point metals such as magnesium and titanium by making the inside of the holding vessel an inert gas atmosphere.