The present invention relates to an apparatus for casting a metal which is suitable for casting a metal used in a field of dentistry, for example, a metal having a high melting point such as a titanium or the like. Further, the present invention relates to a method capable of executing a casting with a higher casting capacity by using the apparatus mentioned above.
Up to the present, a prosthetic appliance has been used at a time of repairing a decayed tooth or a dropout tooth, and the metal having a high melting point, for example, the titanium, a zirconium, a platinum or the like and an alloy thereof is used as a material constituting the prosthetic appliance for the dentistry. Among them, the titanium is particularly a very suitable material in view of a strength, a lightness, a corrosion resistance, a biocompatibility, a cost and the like, and is widely used.
Further, at a time of forming the prosthetic appliance for the dentistry by using the metal mentioned above, a casting mold in which a cavity portion having a desired shape is formed is used, and it is general to directly inject the metal mentioned above in a melting state into the cavity portion of the casing mold so as to mold, and thereafter break the casing mold so as to take out a cast product.
As a general apparatus for casting the metal which has been used, there is a structure in which a tiltable metal crucible 2 is arranged above a casting mold 3 in which a casting cavity 9 is formed, as shown in FIG. 2. The apparatus is structured such that a metal 4 mounted on an upper surface of the crucible 2 is arc-melted in an ambient atmosphere of inert gas (for example, an argon gas), the crucible 2 is tilted at a time when the metal 4 is completely melted, thereby pouring the molten metal into a casting port 5 of the casing mold 3, an opening and closing valve (an electric opening and closing valve) 14 is opened, whereby a pressurized gas flows into an interior portion of a casting chamber 1 from a pressurized gas supply source 13 at a pressure value set by a pressure adjusting device 17, and the interior portion of the casting chamber 1 is gas-pressurized, thereby executing a casting. In this apparatus, the crucible 2 moves so as to tilt to a lower side around a supporting shaft 6 (a supporting point), and stops at a position indicated by reference numeral 2xe2x80x2. In this case, the casting capacity of the apparatus for casting the metal is improved in proportion to the pressure value. In this case, as an electrode rod 10 in a cathode side of the apparatus shown in FIG. 2, a general tungsten electrode rod is used.
However, in the apparatus for casting the metal shown in FIG. 2, since the supporting shaft 6 in the crucible 2 arranged above the casting mold 3 is positioned in a far side from the casting port 5 of the casing mold 3, it is necessary to provide a clearance for preventing the crucible 2 after being tilted from being in contact with the casing mold 3, between the crucible 2 and the casting mold 3, so that the molten metal drops down along a distance larger than the clearance. Since the clearance is generally about 4 to 5 cm, the apparatus mentioned above has a problem that it is hard to drop down the metal in the melding state into the casting cavity 9 within the casting mold 3 with keeping a high temperature, and there is a limit to make the apparatus compact. Further, in the case of the apparatus having the structure mentioned above, since the molten metal drops down at a fixed width, there are problems that the molten metal attaches to a periphery of the casting port 5 and a dispersion is generated in view of the dropping position of the metal.
Further, in the case of this apparatus, since a distance between the metal and the electrode rod is changed (enlarged) when the crucible starts tilting, there is a problem that an arc discharge is immediately stopped and a proper overheat of the molten metal is not absolutely achieved, whereby it is hard to cast the molten metal having the high temperature into the casting mold 3.
Further, aside from this, in the case of the apparatus having the structure shown in FIG. 2, since a pressure value pertinent to the casting capacity is univocally determined by the pressure adjusting device 17, it is necessary to set a set pressure value of the pressure adjusting device 17 to a higher value in the case of intending to obtain a higher casting capacity, and accordingly, there is a problem that it is necessary to reinforce a pressure resisting structure of the casting chamber 1 more. Further, since the gas is supplied to the interior portion of the casting chamber 1 until getting to the pressure value set by the pressure adjusting device 17, there is a problem that a greater amount of gas is consumed in one casting step.
An object of the present invention is to provide an apparatus for a metal casting which can solve the problems mentioned above, and has a structure capable of casting a high temperature metal, in particular a metal having a high melting point for dentistry such as a titanium or the like, in a melting state due to an arc discharge without reducing a temperature.
Further, an another object of the present invention is to provide an apparatus for casting a metal which can use a casting chamber having a simple pressure resisting structure while obtaining a higher casting capacity by utilizing a pressurized gas, and can reduce an amount of consumption of the pressurized gas in the casting step.
Further, the other object of the present invention is to provide a method capable of executing a casting process with a higher casting capacity by using the apparatus mentioned above.
In order to achieve the structure suitable for casting the metal having the high melting point, in accordance with the present invention, there is provided an apparatus for casting a metal comprising:
a crucible 2 and a casting mold 3 provided in an interior portion of a casting chamber 1 capable of controlling an internal pressure;
an electrode rod 10 for melting a metal 4 mounted on the crucible 2 in accordance with an arc discharge, the electrode rod 10 being provided above the crucible 2;
the crucible 2 being tiltable around a supporting shaft 6 in such a manner as to pour the metal 4 melted on the crucible 2 into a casting port 5 of the casting mold 3;
the supporting shaft 6 being positioned in a side of an outflow end portion of the crucible 2 close to the charging port 5; and
a tilting means 7 for drawing up a non-outflow end portion to an upper side so as to tilt the crucible, the tilting means 7 being provided in a side of the non-outflow end portion of the crucible 2,
wherein the supporting shaft 6 is provided at a position at which a clearance between the metal 4 and a front end of the electrode rod 10 is kept substantially constant after the melting of the metal 4 in accordance with the arc discharge on the crucible 2 is started and the melting of the metal 4 makes progress and until the metal 4 in the melting state fluidizes and drops down due to the tilting of the crucible 2, and the arc discharge is controlled so that the arc discharge is carried over between the metal 4 in the melting state and the front end of the electrode rod 10 during a period that the crucible 2 is tilted and the metal 4 in the melting state fluidizes and drops down on the crucible 2.
Further, in accordance with the present invention, there is provided an apparatus for casting a metal having the structure mentioned above, wherein a pressure reduction pump 12 capable of making the interior portion of the casting chamber 1 in a pressure reduced state, and a pressurized gas supply source 13 supplying a pressurized gas to the interior portion of the casting chamber 1 are connected to the casting chamber 1, an inflow of the pressurized gas supplied from the pressurized gas supply source 13 into the casting chamber 1 is controlled by an opening and closing valve 14, the opening and closing valve 14 becomes in an open state at a time when a gas supply pressure P1 of the pressurized gas supply source 13 is larger than a gas pressure P2 required for casting the metal in the melting state into a casting mold cavity 9 of the casting mold 3 with no lack of casting and the metal 4 melted on the crucible 2 is poured into the casting port 5 of the casting mold 3 in accordance with the tilting of the crucible 2, and the inflow of the pressurized gas into the casting chamber 1 is shut off by the opening and closing valve 14 at a timing when the pressurized gas flows into the casting chamber 1 from the pressurized gas supply source 13 and an internal pressure of the casting chamber 1 gets to the gas pressure P2.
Further, in accordance with the present invention, there is provided a metal casting method of casting a metal by using an apparatus for casting a metal having a structure in which a crucible 2 and a casting mold 3 are provided in an interior portion of a casting chamber 1 capable of controlling an internal pressure, an electrode rod 10 for melting a metal 4 mounted on the crucible 2 in accordance with an arc discharge is provided above the crucible 2, the crucible 2 is tiltable around a supporting shaft 6 in such a manner as to pour the metal 4 melted on the crucible 2 into a casting port 5 of the casting mold 3, the supporting shaft 6 is positioned in a side of an outflow end portion of the crucible 2 close to the casting port 5, and is provided at a position at which a clearance between the metal 4 and a front end of the electrode rod 10 is kept substantially constant after the melting of the metal 4 in accordance with the arc discharge on the crucible 2 is started and the melting of the metal 4 makes progress and until the metal 4 in the melting state fluidizes and drops down due to the tilting of the crucible 2, and a tilting means 7 for drawing up a non-outflow end portion to an upper side so as to tilt the crucible is provided in a side of the non-outflow end portion of the crucible 2,
wherein an electric voltage is applied between the metal 4 and the electrode rod 10 so as to generate an arc discharge after mounting the metal 4 on the crucible 2, the crucible 2 is tilted at a timing that the metal 4 is melted so as to become in a state of capable of fluidizing, and the arc discharge is kept between the metal 4 in the melting state and the front end of the electrode rod 10 even during a period that the metal 4 in the melting state fluidizes on the crucible 2 so as to drop down at a time of pouring the metal 4 in the melting state into the casting port 5 of the casting mold 3.
Further, in accordance with the present invention, there is provided a method as recited in the above, wherein an apparatus having a structure in which a pressure reduction pump 12 capable of making the interior portion of the casting chamber 1 in a pressure reduced state, and a pressurized gas supply source 13 supplying a pressurized gas to the interior portion of the casting chamber 1 are connected to the casting chamber 1, and an inflow of the pressurized gas supplied from the pressurized gas supply source 13 into the casting chamber 1 is controlled by an opening and closing valve 14 is used as the apparatus for casting the metal, and in which a gas supply pressure P1 of the pressurized gas supply source 13 is made larger than a gas pressure P2 required for casting the metal in the melting state into a casting mold cavity 9 of the casting mold 3 with no lack of casting, the opening and closing valve 14 is controlled so as to be in an open state at a time when the metal 4 melted on the crucible 2 due to the tilting of the crucible 2 is poured into the casting port 5 of the casting mold 3, and so that the pressurized gas flows into the casting chamber 1 from the pressurized gas supply source 13, and the inflow of the pressurized gas into the casting chamber 1 is shut off by the opening and closing valve 14 at a timing when an internal pressure of the casting chamber 1 gets to the gas pressure P2.