JP2006167755A - Method and apparatus for reduction casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for reduction casting, which apparatus can make a reducing substance effectively react to molten metal without deteriorating the activity of the reducing substance. <P>SOLUTION: A casting apparatus 10 comprises a molten metal supplying bath 16 having a molten metal supplying cylinder 20, and a formed mold 12 having a gate 12b and a cavity 12a. When the molten metal 18 is supplied into the cavity 12a by pressurizing the molten metal 18 stored in the molten metal supplying bath 16, the molten metal is supplied into the cavity while reducing the oxidized film existing on the surface of the molten metal by making the reducing substance 26 react to the molten metal. The casting apparatus 10 further comprises an approaching and separating mechanism for relatively approaching and separating the molten metal supplying cylinder 20 and the gate 12b, a shielding means 22 for surrounding the outer periphery of the opening end side of the molten metal supplying cylinder 20 and the opening end side of the gate 12b and for gas-tightly shielding the portion between the molten metal supplying cylinder and the gate for the outside, and an introducing passage 24 which gas-tightly penetrates the shielding means 22 and introduces the reducing substance 26 into the space 23 surrounded by the shielding means 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reduction casting method and a reduction casting apparatus, and more particularly, to a reduction casting method and a reduction casting apparatus that perform casting by activating a reducing substance using thermal energy of a molten metal.

As a casting method that can be suitably used for casting aluminum or the like, the applicant of the present application can improve the fluidity of the molten metal by causing a reducing substance such as magnesium nitrogen compound (Mg ₃ N ₂ ) to act on the molten metal. Have proposed a reduction casting method that enables simple casting (Patent Document 1, etc.).
In this reduction casting method, as a main method of causing the reducing substance to act on the molten metal, a metal gas (for example, magnesium gas) and a reactive gas (for example, nitrogen gas) are individually introduced into the cavity, After generating the reducing substance, after injecting the molten metal into the cavity and causing the reducing substance to act on the molten metal, after generating the reducing substance by reacting the metal gas and the reactive gas in advance outside the mold There is a method in which a reducing substance is introduced into a cavity by a carrier gas or the like and molten metal is injected into the cavity to cause the reducing substance to act on the molten metal.

The reduction casting method is a method of reducing and casting an oxide film formed on the surface of the molten metal by causing a reducing substance to act on the molten metal. For example, an oxide film is formed on the surface of the molten metal like aluminum or an aluminum alloy. It can be suitably used for casting with a metal that is easily formed. The action of reducing the oxide film (Al ₂ O ₃ ) formed on the surface of the molten aluminum by the magnesium nitrogen compound (Mg ₃ N ₂ ), which is a reducing substance, is due to the following chemical reaction.
Mg ₃ N ₂ + Al ₂ O ₃ → Al + MgO + N ₂
Although MgO remains in the molten metal, since it is a trace amount, it does not affect the properties of the cast product. N ₂ gas is discharged out of the cavity.
According to the reduction casting method, the fluidity of the molten metal becomes good, the hot water circulation property becomes good, and it is possible to easily obtain a high-quality cast product free from hot water wrinkles and the like.

JP 2001-321918 A

  When the reduction casting method described above is applied to actual casting, it is important to make the reducing substance act effectively on the molten metal in order to achieve a suitable reduction casting. The reducing substance is active at high temperatures and has a suitable reducing action on the molten metal. For this reason, it is preferable that the reducing substance deposited in the cavity is kept at a high temperature in the cavity, or the reducing substance generated in the reaction furnace is introduced into the cavity at a high temperature and cast.

By the way, in the case of reduction casting, since the fluidity of the molten metal becomes good, it is possible to perform casting by lowering the mold temperature to about room temperature, thereby shortening the cycle time of casting and improving the production efficiency. It becomes possible. However, when the mold temperature is lowered, the reactivity of the reducing substance decreases and the molten metal rapidly solidifies in the cavity. Therefore, the oxide film on the molten metal surface is reduced by the reducing substance to ensure fluidity. However, there is a problem that it is difficult to adjust so as to ensure the filling property of the molten metal.
In addition, a high-temperature reactor is required to obtain a high-temperature reducible material, or the reductive material is introduced into the mold cavity at a high temperature, so it is necessary to consider the layout of the mold and the reactor. There was a problem that there was.

  Therefore, the present invention has been made to solve these problems, and the object of the present invention is to allow the reducing substance to effectively act on the molten metal without impairing the activity of the reducing substance, Accordingly, it is an object of the present invention to provide a reduction casting method and a reduction casting apparatus that enable suitable reduction casting.

In order to achieve the above object, the present invention comprises the following arrangement.
That is, by having a hot water tank provided with a hot water supply cylinder and a mold having a gate and a cavity communicating with the gate, pressurizing the molten metal stored in the hot water tank and / or reducing the pressure in the cavity A casting apparatus that fills and casts molten metal into the cavity while reducing the oxide film on the surface of the molten metal by applying a reducing substance to the molten metal when filling the molten metal into the cavity through the hot water supply pipe and the gate. A contact / separation mechanism for moving the hot water supply tube and the gate relative to each other, and surrounding an outer periphery of the open end side of the hot water supply tube and the open end side of the gate, and between the hot water supply tube and the gate. A shielding means for shielding airtightly, and an introduction path for airtightly penetrating the shielding means and for introducing a reducing substance into a space surrounded by the shielding means.

Further, the shielding means has one end side fixed to the gate side and the other end side fixed to the hot water tank side, and expands and contracts with the movement when moving relative to the gate of the hot water cylinder. It is a means.
Alternatively, the shielding means is shielding means in which one end side is fixed to the gate side and the other end side is fixed to the hot water tank side, and the hot water cylinder is provided movably with respect to the hot water tank and is connected to the gate. The liquid-tight connection is possible.

Further, the introduction path is provided to be airtightly slidable with respect to the shielding means so as to be able to advance and retreat within a space surrounded by the shielding means.
In addition, the introduction path includes an introduction path for introducing a reactive gas into a space surrounded by the shielding means, and an introduction path for introducing metal powder.

Further, the reduction casting method according to the present invention is a reduction casting method using the above reduction casting apparatus, the step of moving the hot water supply tube relative to the gate by the contact / separation mechanism, and the shielding means. A step of supplying a reducing substance from the introduction path into the enclosed space, a step of liquid-tightly coupling the hot water supply cylinder and the gate, pressurizing the molten metal stored in the hot water tank, and / or By reducing the pressure inside the cavity, the molten metal is filled into the cavity via the hot water supply cylinder and gate, and at that time, the reducing material is allowed to act on the molten metal to reduce the oxide film on the molten metal, and the molten metal is filled into the cavity. And a casting step.

In addition, the reducing substance introduced into the space surrounded by the shielding means is activated by the heat of the molten metal.
The reducing gas may be generated by reacting the reactive gas introduced into the space surrounded by the shielding means with the metal powder by the heat of the molten metal.
Further, a molten aluminum or aluminum alloy is used as the molten metal, and a magnesium nitrogen compound is used as the reducing substance.

  According to the reduction casting method and the reduction casting apparatus according to the present invention, as described above, after supplying the reducing substance to the hot water supply cylinder or the cavity of the mold, the molten metal is poured into the cavity from the hot water supply pipe and cast. The reducing substance is heated and activated by the heat of the molten metal in the hot water supply cylinder, and the oxide film formed on the surface of the molten metal injected into the cavity can be effectively reduced, and the fluidity of the molten metal is increased. This makes it possible to perform hot casting and to perform high-quality reduction casting. In addition, since the fluidity of the molten metal becomes good, it is possible to cast the molten metal at a high speed by lowering the mold temperature, which enables efficient and high quality casting. In addition, since the reducing substance is heated by the heat of the molten metal itself in the hot water supply cylinder, it is not necessary to prepare a separate heating furnace for heating the reducing substance, which can save energy and There are significant effects such as easy layout.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram showing the overall configuration of a casting apparatus 10 according to the present invention. The casting apparatus 10 of this embodiment is used for aluminum casting by LPD (low pressure die casting).
In FIG. 1, 12 is a mold, and 12 a is a cavity provided in the mold 12. Reference numeral 14 denotes a vacuum suction device provided in communication with the cavity 12a. Reference numeral 16 denotes a hot water supply tank for the molten metal 18, and reference numeral 20 denotes a hot water supply pipe for connecting the hot water supply tank 16 and the mold 12.
The hot water supply cylinder 20 moves up and down with respect to the hot water tank 16 by a contact / separation mechanism (not shown) including a rack and a pinion.

In the LPD device, the mold 12 is disposed above the hot water tank 16 and pressure is applied to the molten metal 18 in the hot water tank 16 so that the molten metal 18 stored in the hot water tank 16 via the hot water cylinder 20 is cavity. 12a is filled and cast. During the casting, as shown in FIG. 2, the hot water supply cylinder 20 is raised by a contact / separation mechanism (not shown), and the hot water supply cylinder 20 is in liquid-tight contact with (connected to) the gate 12b of the mold 12. The molten metal is injected into the cavity 12a. It is also possible to use a method in which vacuum suction is performed from the vacuum suction device 14, the inside of the cavity 12a is decompressed, and the molten metal 18 is filled into the cavity 12a from the hot water supply cylinder 20.

The characteristic feature of the casting apparatus 10 of the present embodiment is that the outer periphery of the open end side of the hot water supply cylinder 20 and the open end side of the gate 12b is enclosed, and the space between the hot water supply cylinder 20 and the gate 12b is airtight to the outside. A shielding means 22 for shielding, and an introduction path 24 that penetrates the shielding means 22 in an airtight manner and introduces a reducing substance (magnesium nitrogen compound: Mg ₃ N ₂ ) 26 into a space 23 surrounded by the shielding means 22. It is provided that the reducing substance supplied into the space 23 is cast by being heated by the heat of the molten metal 18.

The shielding means 22 has a cylindrical shape, and is fixed to the lower surface of the mold 12 so that one end side surrounds the gate 12b, and is fixed to the upper surface of the hot water tank 16 so that the other end side surrounds the hot water supply tube 20.
The introduction path 24 is provided so as to be slidable in an airtight manner with respect to the shielding means 22 so that the distal end side can move forward and backward in the space 23. The leading end side of the introduction path 24 is bent downward, and is provided so that the reducing substance can be ejected into the open end of the hot water supply cylinder 20 at the advanced position. When the hot water supply cylinder 20 rises, the introduction path 24 moves backward in the space 23 (see FIG. 2) so that the hot water supply pipe 20 does not get in the way.

Reference numeral 25 denotes an introduction path for introducing an inert gas such as argon gas into the space 23. The introduction path 25 is also slidable in an airtight manner with respect to the shielding means 22 so that the distal end side can advance and retreat in the space 23. A container 28 containing a reducing substance 26 communicates with the introduction path 24 via a pipe 27, and the container 28 is connected to an argon gas cylinder 34 via a valve 30 and a pipe 32. The introduction path 25 and the pipe 32 are connected by a pipe 36 via a valve 38.
In addition, a mechanism such as a cylinder device can be appropriately adopted as the advancing / retracting mechanism of the both introduction paths 24 and 25.

The casting operation using the casting apparatus 10 of the present embodiment is performed as follows.
First, the hot water supply cylinder 20 is lowered, and both the introduction paths 24 and 25 are in the forward position (FIG. 1). In this state, air is exhausted from the cavity 12 a by the vacuum suction device 14. At this time, the valve 38 is opened and argon gas is fed from the argon gas cylinder 34 into the hot water supply cylinder 20 through the introduction path 25. As a result, the inside of the hot water supply cylinder 20 and the cavity 12a are filled with argon gas, and the inside of the hot water supply cylinder 20 and the cavity 12a becomes a non-oxidizing atmosphere. It is possible to purge the hot water supply cylinder 20 and the air in the cavity 12a with argon gas without using the vacuum suction device 14, but it is more efficient to use the vacuum suction device 14.
After the hot water supply cylinder 20 and the cavity 12a are filled with argon gas, the valve 38 is closed.

Next, the reducing substance 26 is introduced into the hot water supply cylinder 20. That is, the valve 30 is opened, the reducing substance 26 is sent from the container 28 into the space 23 through the pipe 27 and the introduction path 24 using the argon gas pressure of the argon gas cylinder 34, and the argon gas pressure is used. It is injected into the hot water supply cylinder 20. The container 28 may contain the reducing substance 26 in an amount to be used in one injection using the argon gas pressure.
By injecting the reducing substance 26 into the hot water supply cylinder 20 using the argon gas pressure, the reducing substance 26 fills the inside of the hot water supply cylinder 20 and is also fed into the space 23 and the cavity 12a of the mold 12. Is done.

  By injecting the reducing substance 26 into the hot water supply cylinder 20 using the argon gas pressure, the reducing substance 26 becomes gaseous and fills the hot water supply pipe 20 and is stored in the hot water tank 16. It is easily heated by the heat of the molten metal 18. In addition, the reducing substance 26 fed into the hot water supply cylinder 20 enters the cavity 12 a of the mold 12. In the hot water tank 16, the molten aluminum 18 is heated to about 740 ° C.

  After the reducing substance 26 is injected from the container 28 to the hot water supply cylinder 20 using the argon gas pressure, the valve 30 is closed and the introduction paths 24 and 25 are moved backward. Next, the hot water supply cylinder 20 is raised, and the hot water supply cylinder 20 is liquid-tightly connected to the gate 12b as shown in FIG. In this state, a pressure is applied to the molten aluminum 18 stored in the hot water tank 16, the aluminum molten metal 18 is pushed up into the hot water supply cylinder 20, and the molten metal is introduced into the cavity 12a through the gate 12b.

As described above, the reducing substance (magnesium nitrogen compound: Mg ₃ N ₂ ) 26 supplied to the hot water supply cylinder 20 is heated in the hot water supply cylinder 20 by the heat of the molten aluminum 18 and is sufficiently activated. It has become. Therefore, the reducing substance 26 effectively acts on the molten aluminum 18 pushed up in the hot water supply cylinder 20, and the oxide film formed on the surface of the molten aluminum 18 can be effectively reduced. . As a result, the fluidity of the molten metal 18 filled in the cavity 12a from the hot water supply cylinder 20 becomes good, and the molten aluminum 18 is injected into the cavity 12a in a state of high fluidity.

A part of the reducing substance 26 supplied to the hot water supply cylinder 20 has a reducing action with the molten aluminum 18 in the hot water supply cylinder 20, but the rest is sent to the cavity 12 a so as to be pushed by the molten aluminum 18. Entered.
The reducing substance 26 previously fed into the cavity 12 a is activated by being heated by the heat of the molten aluminum 18, and the reducing substance 26 fed into the cavity 12 a together with the molten aluminum 18 from the hot water supply cylinder 20. Since the substance 26 is also in an activated state, when the cavity 12a is filled with the molten aluminum 18, the reducing action by the reducing substance 26 is sufficiently performed, and the fluidity of the molten aluminum 18 is sufficient. Thus, it is possible to fill the cavity 12a with the molten metal 18.

In the case of the casting apparatus 10 according to the present embodiment, the reducing substance (magnesium nitrogen compound: Mg ₃ N ₂ ) 26 is heated sufficiently in the hot water supply cylinder 20 immediately before the molten metal 18 is injected into the cavity 12a. Since it is in an activated state, it has a layout that functions most effectively as the action of the reducing substance 26 used for the purpose of improving the fluidity of the molten metal 18, and the reducing substance 26 is also used in the cavity 12 a. The reduction action of is effective.
Therefore, by providing the mold 12 as a coating-less and lowering the mold temperature by water cooling or applying a surface treatment with good thermal conductivity, a casting method capable of high-speed solidification without deteriorating the quality of the cast product is provided. It becomes possible.

  As described above, in the casting apparatus of the present embodiment, the reducing substance 26 is activated using the heat of the molten metal 18 stored in the hot water tank 16, and it is not necessary to use a special heat source, thus saving energy. This is also useful in that it can be achieved.

FIG. 3 is an explanatory view showing a second embodiment of the casting apparatus 10 according to the present invention. The same members as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the present embodiment, magnesium powder is introduced into the hot water supply cylinder 20 from the introduction path 25, and nitrogen gas as a reactive gas is introduced from the introduction path 24 to generate a reducing substance inside the hot water supply cylinder 20. I am doing so. In FIG. 3, 40 is an argon gas cylinder, 44 is a tank containing magnesium powder, and 47 is a nitrogen gas cylinder.

First, by opening the valve 43 and closing the valve 45, argon gas is introduced from the argon gas cylinder 40 through the pipes 41 and 42 and the introduction path 25 into the hot water supply cylinder 20 and the cavity 12 a. Next, by closing the valve 43 and opening the valve 45, the magnesium powder in the tank 44 is introduced into the hot water supply cylinder 20 through the pipe 46 and the introduction path 25 by being put on the argon gas flow. At the same time, the nitrogen gas is introduced into the hot water supply cylinder 20 from the nitrogen gas cylinder 47 through the pipe 48 and the introduction path 24 by opening the valve 49. Magnesium metal is sublimated at 700 ° C. to 850 ° C. to become magnesium gas. This magnesium gas reacts with the nitrogen gas to produce a magnesium nitrogen compound inside the hot water supply cylinder 20 and also flows into the cavity 12a.

In this way, after the magnesium nitrogen compound is generated in the hot water supply cylinder 20 and the cavity 12a, the hot water supply cylinder 20 is raised (FIG. 3), and the hot water supply cylinder 20 is connected to the gate 12b in a liquid-tight manner. In this state, pressure is applied to the molten aluminum 18 stored in the hot water tank 16, the molten aluminum 18 is pushed up into the hot water supply cylinder 20, and the molten metal is introduced into the cavity 12a through the gate 12b.

4 and 5 are explanatory views showing a third embodiment of the casting apparatus according to the present invention. In the present embodiment, as shown in FIG. 4, the shielding means 22 is configured by fitting a large number of cylindrical bodies. The shielding means 22 is formed in a cylindrical shape that can be expanded and contracted in the vertical direction by providing adjacent cylindrical bodies so that they can slide forward and backward.
In the present embodiment, the hot water tank 16 and the hot water supply cylinder 22 are fixedly provided, and the hot water tank 16 and the hot water supply cylinder 22 are provided so as to move toward and away from the gate 12b. The shielding means 22 expands and contracts along with this contact / separation movement. In addition, you may provide so that the shaping | molding die 12 side may contact / separate toward the hot-water supply tank 16 side, or you may provide so that both the shaping | molding die 12 and the hot-water supply tank 16 may be contacted / separated.
Other configurations are the same as those shown in FIG. 1 and FIG.

In the present embodiment, first, the hot water supply cylinder 20 is moved away from the gate 12b by a contact / separation mechanism (not shown). Therefore, the shielding means 22 extends.
Further, both the introduction paths 24 and 25 are moved forward, the vacuum suction device 14 is operated in the same manner as described above, and argon gas is introduced from the introduction path 25 into the space 23, the hot water supply cylinder 20, and further into the cavity 12 a. Next, the reducing substance 26 is introduced into the hot water supply cylinder 20 from the introduction path 24. Thereby, the reducing substance 26 is also filled in the hot water supply cylinder 20, the space 23, and the cavity 12a.

Next, as shown in FIG. 5, both introduction paths 24 and 25 are moved backward, the contact / separation mechanism is driven to bring the hot water supply cylinder 20 and the gate 12b closer relative to each other (the shielding means 22 is contracted), and contact. Let them be liquid-tightly connected. In this state, a pressure is applied to the molten aluminum 18 stored in the hot water tank 16, the aluminum molten metal 18 is pushed up into the hot water supply cylinder 20, and the molten metal is introduced into the cavity 12a through the gate 12b.

The reducing substance (magnesium nitrogen compound: Mg ₃ N ₂ ) 26 supplied to the hot water supply cylinder 20 is heated in the hot water supply cylinder 20 by the heat of the molten aluminum 18 and is in a sufficiently activated state. Therefore, the reducing substance 26 effectively acts on the molten aluminum 18 pushed up in the hot water supply cylinder 20, and the oxide film formed on the surface of the molten aluminum 18 can be effectively reduced. . As a result, the fluidity of the molten metal 18 filled in the cavity 12a from the hot water supply cylinder 20 becomes good, and the molten aluminum 18 is injected into the cavity 12a in a state of high fluidity.

A part of the reducing substance 26 supplied to the hot water supply cylinder 20 has a reducing action with the molten aluminum 18 in the hot water supply cylinder 20, but the rest is sent to the cavity 12 a so as to be pushed by the molten aluminum 18. Entered.
The reducing substance 26 previously fed into the cavity 12 a is activated by being heated by the heat of the molten aluminum 18, and the reducing substance 26 fed into the cavity 12 a together with the molten aluminum 18 from the hot water supply cylinder 20. Since the substance 26 is also in an activated state, when the cavity 12a is filled with the molten aluminum 18, the reducing action by the reducing substance 26 is sufficiently performed, and the fluidity of the molten aluminum 18 is sufficient. Thus, it is possible to fill the cavity 12a with the molten metal 18.

  Also in this embodiment, instead of injecting the reducing substance 26 into the hot water supply cylinder 20, magnesium powder and a reactive gas such as nitrogen gas are individually injected to reduce the reductivity in the cavity 12 a and the hot water supply cylinder 20. It is also possible to produce a substance and perform reduction casting.

It is explanatory drawing which shows the structure of 1st Embodiment of the reduction | restoration casting apparatus which concerns on this invention. It is explanatory drawing which shows the state which raised the hot-water supply pipe | tube. It is explanatory drawing which shows 2nd Embodiment of the casting apparatus which concerns on this invention. It is explanatory drawing of the shielding means provided in the 3rd Embodiment of the casting apparatus which concerns on this invention so that expansion-contraction was possible. It is explanatory drawing which shows the state which provided the shielding means of FIG. 4, and connected the hot-water supply pipe | tube and the gate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Casting apparatus 12 Mold 12a Cavity 12b Gate 14 Vacuum suction apparatus 16 Hot water tank 18 Molten metal 20 Hot water supply cylinder 22 Shielding means 23 Space 24 Introduction path 25 Introduction path 26 Reducing substance 34 Argon gas cylinder 40 Argon gas cylinder 46 Tank 47 Nitrogen gas cylinder

Claims (9)

A hot water supply tank having a hot water supply pipe and a mold having a gate and a cavity communicating with the gate, and pressurizing the molten metal stored in the hot water tank and / or depressurizing the inside of the cavity, thereby supplying hot water When filling the cavity with the molten metal through the cylinder and the gate, a casting apparatus for casting the molten metal in the cavity while reducing the oxide film on the surface of the molten metal by acting a reducing substance on the molten metal,
A contact / separation mechanism for moving the hot water supply tube and the gate relative to each other.
Shielding means that surrounds the outer periphery of the open end side of the hot water supply cylinder and the open end side of the gate, and shields the space between the hot water supply pipe and the gate from the outside.
A reduction casting apparatus characterized by comprising an introduction path for airtightly penetrating the shielding means and introducing a reducing substance into a space surrounded by the shielding means. The shield means is an extendable shield means having one end fixed to the gate side and the other end fixed to the hot water tank side, and expands and contracts with the movement when moving relative to the gate of the hot water cylinder. The reduction casting apparatus according to claim 1, wherein the reduction casting apparatus is provided. The shielding means is a shielding means in which one end side is fixed to the gate side and the other end side is fixed to the hot water tank side,
2. The reduction casting apparatus according to claim 1, wherein the hot water supply cylinder is provided movably with respect to the hot water supply tank and can be liquid-tightly connected to the gate. The said introduction path is provided so that it can slide airtightly with respect to the said shielding means so that it can advance and retreat within the space enclosed by the said shielding means. The reduction casting apparatus according to item. The said introduction path comprises the introduction path which introduce | transduces reactive gas in the space enclosed by the said shielding means, and the introduction path which introduces metal powder, The any one of Claims 1-4 characterized by the above-mentioned. The reduction casting apparatus as described. A reduction casting method using the reduction casting apparatus according to any one of claims 1 to 5,
A step of separating the hot water supply tube relative to the gate by the contact / separation mechanism;
Supplying a reducing substance from the introduction path into the space surrounded by the shielding means;
Next, a step of liquid-tightly coupling the hot water supply cylinder and the gate;
By pressurizing the molten metal stored in the hot water tank and / or depressurizing the cavity, the molten metal is filled into the cavity through the hot water cylinder and the gate, and the reducing substance is allowed to act on the molten metal at that time. And a step of casting the molten metal in the cavity while reducing the surface oxide film. The reduction casting method according to claim 6, wherein the reducing substance introduced into the space surrounded by the shielding means is activated by the heat of the molten metal. 7. The reduction casting method according to claim 6, wherein the reducing gas is generated by reacting the reactive gas introduced into the space surrounded by the shielding means with the metal powder by the heat of the molten metal.   9. The reduction casting method according to claim 6, wherein a molten aluminum or aluminum alloy is used as the molten metal, and a magnesium nitrogen compound is used as the reducing substance.

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