JP3604347B2 - Reduction casting method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reduction casting method for casting while reducing an oxide film formed on the surface of a molten metal.
[0002]
[Prior art]
There are various casting methods such as gravity casting (GDC), low pressure casting (LPDC), die casting (DC), squeeze (SC), and thixomold. In each of these methods, a molten metal is injected into a cavity of a molding die and molded into a predetermined shape. Among these casting methods, those in which an oxide film is easily formed on the surface of the molten metal, for example, in aluminum casting, the surface tension is increased by the oxide film formed on the surface of the molten metal. There is a problem that the weldability is reduced and casting defects such as unfilled molten metal and hot lines are generated.
[0003]
As a method for solving these problems, the present applicant has developed a reduction casting method for reducing and casting an oxide film formed on the surface of a molten metal. In the casting of aluminum, which is an example to which this reduction casting method is applied, a magnesium nitrogen compound (Mg ₃ N ₂ ) having a strong reducing property is generated using nitrogen gas and magnesium gas, and this magnesium nitrogen compound is melted into a molten aluminum. To reduce and cast the oxide film formed on the surface of the molten metal. By pouring the molten metal with the magnesium nitrogen compound precipitated on the surface of the cavity of the mold, when the molten metal comes into contact with the surface of the cavity, the oxide film on the surface of the molten metal is reduced and the surface tension of the molten metal is reduced, The fluidity and wettability of the molten metal are improved, and it is possible to produce a cast product having an excellent appearance without casting defects such as unfilled molten metal.
[0004]
[Problems to be solved by the invention]
The above reduction casting method is characterized in that an oxide film formed on the surface of a molten metal is reduced by causing a reducing compound such as a magnesium nitrogen compound to act on the molten metal. Since this reducing compound has a strong reducing property, it needs to be generated in a non-oxygen atmosphere. At the same time, however, there is a problem that the reducing compound easily reacts with the water present in the cavity of the mold, thereby losing the reducing property. The magnesium nitrogen compound easily reacts with water to become magnesium oxide, and when it becomes magnesium oxide, it loses its original reducing ability.
[0005]
Thus, when the reducing compound introduced into the cavity of the mold or the reducing compound generated in the cavity loses the reducing property, the function of casting by reducing the oxide film on the surface of the molten metal acts. And the required reduction casting cannot be performed. For example, when the humidity is not controlled in the working environment in the high humidity season, the reducing action of the reducing compound precipitated in the cavity does not work because the humidity also increases in the cavity of the mold, The required reduction casting may not be performed. As described above, when the reducing action by the reducing compound is not exerted, since there is no difference from the casting method by the ordinary heavy-weight casting method or the like, the advantage of the reduction casting method such as improvement of the molten metal flowability cannot be obtained. Problems arise.
[0006]
Therefore, the present invention has been made to solve these problems, and an object of the present invention is to prevent the reducing property of a reducing compound used for the purpose of utilizing a reducing action in reduction casting from being impaired. Another object of the present invention is to provide a reduction casting method capable of reliably reducing an oxide film on the surface of a molten metal, thereby enabling an effective reduction casting.
[0007]
[Means for Solving the Problems]
The present invention has the following configuration to achieve the above object.
That is, in a reduction casting method in which a molten metal is poured into a cavity of a molding die, and the molten metal is brought into contact with a reducing compound in the cavity of the molding die to cast an oxide film formed on the surface of the molten metal while reducing. After reducing the humidity in the cavity to at least 70%, a reducing compound is introduced into the cavity, and then the molten metal is poured into the cavity and cast.
Further, a dry gas that does not react with the reducing compound is introduced into the cavity to dehumidify the cavity, and then the reducing compound is introduced into the cavity.
Further, the method is characterized in that a molten metal of aluminum or an alloy thereof is used as the molten metal of the metal, and casting is performed by introducing magnesium nitrogen gas as a reducing compound into a mold.
[0008]
In a reduction casting method, a molten metal is poured into a cavity of a molding die, and the molten metal is brought into contact with a reducing compound in a cavity of the molding die to cast an oxide film formed on the surface of the molten metal while reducing. After reducing the humidity in the cavity to at least 70% or less, a metal gas and a reactive gas are introduced into the cavity to generate the reducing compound in the cavity, and then the molten metal is poured into the cavity. It is characterized by hot casting.
In addition, a dry gas that does not react with the reducing compound is introduced into the cavity to dehumidify the cavity, and then a reducing gas is generated in the cavity by introducing a metal gas and a reactive gas into the cavity. It is characterized by.
Further, a reactive gas is used as the dry gas.
In addition, a molten metal of aluminum or an alloy thereof is used as the molten metal of the metal, a magnesium gas is introduced as a metal gas into the molding die, and a nitrogen gas is introduced as a reactive gas to generate a reducing compound in the cavity and cast. It is characterized by.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view showing the overall configuration of a casting apparatus 10 in which the reduction casting method according to the present invention is applied to aluminum casting.
Reference numeral 12 denotes a molding die for pouring aluminum or an aluminum alloy to obtain a cast product. The mold 12 is provided with a gate 12a, a cavity 12b, a metal gas inlet 12c, a feeder unit 16, and an exhaust hole 25.
[0010]
The molding die 12 is connected to the nitrogen gas cylinder 20 by a pipe 22, and by opening a valve 24 of the pipe 22, nitrogen gas is injected into the cavity 12 b from the nitrogen gas inlet 12 d and the inside of the cavity 12 b is substantially changed to a nitrogen gas atmosphere. A non-oxygen atmosphere can be used. In this case, the inside of the cavity 12b can be dehumidified by using a dry gas as the nitrogen gas. Further, an air cylinder 18 may be connected to the nitrogen gas inlet 12d of the mold 12 via a pipe 22 to introduce dry air into the cavity 12b for dehumidifying the cavity 12b.
[0011]
The argon gas cylinder 19 is connected to a heating furnace 28 as a generator for generating a metal gas through a pipe 26, and an argon gas is injected into the heating furnace 28 by opening a valve 30 provided in the pipe 26. The inside of the heating furnace 28 is formed so as to be heatable by a heater 32, and the temperature in the furnace is set to 800 ° C. or higher at which magnesium powder sublimes in order to generate magnesium gas as a metal gas. The amount of argon gas injected into the heating furnace 28 can be adjusted by adjusting the valve 30.
[0012]
The argon gas cylinder 19 is connected to a tank 36 containing magnesium powder by a pipe 34 in which a valve 33 is interposed, and the tank 36 is connected to a pipe 26 downstream of the valve 30 by a pipe 38. . A valve 40 that controls the supply amount of magnesium powder to the heating furnace 28 is provided in the pipe 38. The heating furnace 28 is connected to the metal gas inlet 12c of the mold 12 through a pipe 42, and the magnesium gas gasified in the heating furnace 28 is introduced into the cavity 12b through the metal gas inlet 12c. You. The valve 45 interposed in the pipe 42 is for adjusting the supply amount of the metal gas to be injected into the cavity 12b of the molding die 12.
[0013]
The casting of aluminum using the casting apparatus 10 of the present embodiment is performed as follows.
First, the valve 24 is opened, nitrogen gas is injected into the cavity 12b of the mold 12 from the nitrogen gas cylinder 20 via the pipe 22, and the air in the cavity 12b is exhausted by the nitrogen gas. The air in the cavity 12b is exhausted from the exhaust hole 25 of the molding die 12, and the inside of the cavity 12b becomes a nitrogen gas atmosphere and becomes a substantially non-oxygen atmosphere.
The purpose of discharging the air in the cavity 12b with this nitrogen gas is to make the cavity 12b a non-oxygen atmosphere and to dehumidify the inside of the cavity 12b. For this reason, a dry gas is used as the nitrogen gas, and the inside of the cavity 12b is set to a non-oxygen atmosphere while dehumidifying.
[0014]
As a method of dehumidifying the inside of the cavity 12b, instead of using a dry gas of nitrogen gas, dry air is injected into the cavity 12b from the air cylinder 18 via the nitrogen gas inlet 12d to dehumidify the inside of the cavity 12b. Alternatively, nitrogen gas may be injected from the nitrogen gas cylinder 20 into the cavity 12b. By exhausting the air in the cavity 12b with the dry air and sufficiently dehumidifying the inside of the cavity 12b, the inside of the cavity 12b can be controlled to a predetermined humidity or less without using a dry gas as the nitrogen gas.
Alternatively, a gas that does not react with a reducing compound other than nitrogen gas, for example, a dry gas such as an argon gas, may be injected into the cavity 12b to make the inside of the cavity 12b non-oxygen and dehumidified. is there.
It is effective to set the environment in which the casting apparatus 10 is installed as a dehumidified environment, and to maintain the surrounding environment so that at least the humidity in the cavity 12b is 70% or less.
[0015]
On the other hand, while the air in the cavity 12b of the molding die 12 is being exhausted, the valve 30 is opened and argon gas is injected into the heating furnace 28 from the argon gas cylinder 19, and the inside of the heating furnace 28 is brought into an oxygen-free state. I do.
Next, the valve 30 is closed, the valve 40 is opened, and the magnesium powder in the tank 36 is fed into the heating furnace 28 together with the argon gas by the argon gas pressure. Since the heating furnace 28 is heated to a furnace temperature of 800 ° C. or more at which the magnesium powder sublimes, the magnesium powder sent to the heating furnace 28 is sublimated into magnesium gas.
[0016]
Next, the valve 40 is closed, the valve 30 and the valve 45 are opened, and a magnesium gas is injected into the cavity 12b from the metal gas inlet 12c of the mold 12 while adjusting the pressure and the flow rate of the argon gas.
After the magnesium gas is injected into the cavity 12b, the valve 45 is closed, the valve 24 is opened, and the nitrogen gas is injected into the cavity 12b from the nitrogen gas inlet 12d. By injecting the nitrogen gas into the mold 12, the magnesium gas and the nitrogen gas react in the cavity 12b to generate a magnesium nitrogen compound (Mg ₃ N ₂ ). The magnesium nitrogen compound precipitates as a powder on the inner wall surface of the cavity 12b.
[0017]
When the nitrogen gas is injected into the cavity 12b, the pressure and the flow rate of the nitrogen gas are appropriately adjusted. Nitrogen gas may be preheated so that the nitrogen gas and the magnesium gas easily react with each other and injected so that the temperature of the mold 12 does not decrease. The reaction time may be about 5 to 90 seconds (preferably about 15 to 60 seconds). Even if the reaction time is longer than 90 seconds, the mold temperature of the mold 12 decreases, and the reactivity tends to decrease.
[0018]
Magnesium nitride compound deposited on the inner wall surface of the cavity 12b of the mold 12 (Mg 3 _{N 2)} is a highly-reducible compound. In the casting apparatus 10 of the present embodiment, since the environment inside the cavity 12b is previously dehumidified, the magnesium nitrogen compound generated in the cavity 12b can be prevented from combining with the water in the cavity 12b, and the reduction of the magnesium nitrogen compound can be prevented. Nature can be maintained.
[0019]
FIG. 3 is a graph showing how the reactivity between a magnesium nitrogen compound and water changes with humidity. The magnesium nitrogen compound becomes more reactive with increasing humidity, and becomes less reactive with decreasing humidity. In the reduction casting method, the humidity that enables a suitable reduction casting is 70% or less, particularly preferably 65% or less. Therefore, when dehumidifying the inside of the cavity 12b, the humidity in the cavity 12b is preferably set to 70% or less, particularly preferably 65% or less.
[0020]
After the magnesium nitrogen compound is generated in the cavity 12b, the valve 24 is closed, and a molten aluminum is poured from the gate 12a of the molding die 12. The molten metal is injected into the cavity 12b from the gate 12a via the feeder unit 16. The injection of the molten metal is continued until the cavity 12b, the feeder 16 and the gate 12a are filled with the molten metal.
When the molten metal is poured, the molten aluminum is brought into contact with the magnesium nitrogen compound deposited on the inner wall surface of the cavity 12b, and the magnesium nitrogen compound deprives the oxide film on the surface of the molten metal of oxygen, so that the surface of the molten metal becomes pure. Reduced to aluminium.
Further, the oxygen remaining in the cavity 12b reacts with the magnesium nitrogen compound to become magnesium oxide or magnesium hydroxide and is taken into the molten metal. Magnesium oxide and the like thus produced are small and stable compounds, and therefore do not adversely affect the quality of the aluminum casting.
[0021]
The reduction casting method is a method in which oxygen is removed from the oxide film on the surface of the molten metal to form a pure metal surface while the cavity 12b is filled with the molten metal and cast. In the case of the present embodiment, a magnesium nitrogen compound is used. Takes oxygen from the oxide film on the surface of the molten aluminum and casts the surface of the molten metal as pure aluminum. Therefore, it is extremely important for effective reduction casting to dehumidify the interior of the cavity 12b in advance so that the moisture in the cavity does not impair the reducibility of the reducing compound.
Since casting can be performed without forming an oxide film on the surface of the molten metal, the surface tension of the molten metal can be prevented from being increased by the oxide film during the casting process, and the wettability, fluidity and flowability of the molten metal can be improved. Can be. As a result, it is possible to obtain a good cast product having excellent transferability (smoothness) with the inner wall surface of the cavity 12b and free of hot water wrinkles and the like.
[0022]
In addition, since the meltability of the molten metal becomes extremely good, there is no need to provide a large-volume feeder provided in a forming die by a conventional gravity casting method. This is because the molten metal has good meltability and fluidity, so that the entire interior of the cavity 12b can be quickly filled with the molten metal without using the riser action by the riser. Also in the case of the present embodiment, the volume of the feeder unit 16 is set to a limited volume. By reducing the volume of the feeder 16, the amount of the unnecessary portion after casting can be reduced, energy can be saved, and the operation of removing the unnecessary portion from the casting becomes easy. is there.
[0023]
FIG. 2 is an explanatory view showing the configuration of another embodiment of the casting apparatus 10 in which the reduction casting method according to the present invention is applied to aluminum casting.
In the present embodiment, the mold 12 is connected to the pouring tank 15, and the tenon 16 is pulled up, whereby a required amount of molten aluminum 50 is poured into the cavity 12 b from the pouring tank 15.
Reference numeral 20 denotes a nitrogen gas cylinder which is connected to the mold 12 via a pipe 22 and opens a valve 24 to introduce nitrogen gas into the mold 12 and discharge air from the mold 12. ing.
[0024]
In the present embodiment, the nitrogen gas cylinder 20 is a reducing compound that discharges air in the cavity 12b to make the inside of the cavity 12b a non-oxygen atmosphere, dehumidifies the inside of the cavity 12b, and generates outside the molding die 12. It has a function of transporting the magnesium nitrogen compound to the cavity 12b.
In order to dehumidify the inside of the cavity 12b, the air in the cavity 12b can be dehumidified by using a dry gas of nitrogen gas to discharge the air. Instead of using a dry gas of nitrogen gas, dry air is introduced into the cavity 12b from the air cylinder 18 via the nitrogen gas inlet 12d to dehumidify the cavity 12b, and then nitrogen is introduced into the cavity 12b from the nitrogen gas cylinder 20. Gas may be injected. Instead of using a dry gas of nitrogen gas, a dry gas that does not react with the reducing compound may be injected into the cavity 12b to dehumidify the inside of the cavity 12b with a non-oxygen atmosphere.
[0025]
The nitrogen gas cylinder 20 is also connected to a heating furnace 28 through a pipe 26, and a nitrogen gas can be introduced into the heating furnace 28 by opening a valve 30. The furnace temperature of the heating furnace 28 is set to 800 ° C. or higher at which the magnesium powder sublimes.
The nitrogen gas cylinder 20 is also connected via a pipe 34 to a tank 36 containing magnesium powder, and the tank 36 is connected by a pipe 38 to the pipe 26 downstream of the valve 30. A valve 40 is interposed in the pipe 38. The heating furnace 28 is connected to the mold 12 via a pipe 42 and a pipe 44 that penetrates the tenon 15 and communicates with the cavity 12 b of the mold 12.
[0026]
The casting of aluminum using the casting apparatus 10 of the present embodiment is performed as follows.
First, the valve 24 is opened, nitrogen gas is injected into the cavity 12b of the mold 12 from the nitrogen gas cylinder 20 via the pipe 22, and the air in the cavity 12b is exhausted by the nitrogen gas. As a result, the interior of the cavity 12b becomes substantially a non-oxygen atmosphere. By using a dry gas as the nitrogen gas, the inside of the cavity 12b is dehumidified to a humidity of 70% or less. Instead of using a dry gas of nitrogen gas, a dry gas that does not react with the reducing compound, for example, an argon gas is injected into the cavity 12b to make the inside of the cavity 12b a non-oxygen atmosphere and dehumidify the inside of the cavity 12b. be able to. Also in the case of the present embodiment, it is effective to set the environment in which the casting apparatus 10 is installed as a dehumidified environment, and to maintain the surrounding environment so that at least the humidity in the cavity 12b is 70% or less.
[0027]
Next, the valve 30 is opened, and nitrogen gas is introduced into the heating furnace 28.
Next, the valves 24 and 30 are closed, the valve 40 is opened, and the magnesium powder contained in the tank 36 is fed into the heating furnace 28 together with the nitrogen gas by the nitrogen gas pressure of the nitrogen gas cylinder 20. Since the heating furnace 28 is heated to a furnace temperature of 800 ° C. or more at which the magnesium powder sublimates, the magnesium powder sublimates and reacts with nitrogen gas, and a gaseous magnesium nitrogen compound (Mg ₃ N) is formed in the heating furnace 28. ₂ ) is generated.
[0028]
The valve 40 is closed, the valve 30 is opened, and the gaseous magnesium nitrogen compound generated in the heating furnace 28 is supplied to the cavity 12 b of the mold 12 via the pipe 42 and the pipe 44 by the nitrogen gas pressure of the nitrogen gas cylinder 20. inject. The magnesium nitrogen compound (Mg ₃ N ₂ ) injected into the cavity 12b precipitates as a powder on the inner surface of the cavity 12b.
[0029]
With the magnesium nitrogen compound precipitated on the inner surface of the cavity 12b, the tenon 15 is pulled up, so that the molten aluminum 50 in the pouring tank 14 is injected into the cavity 12b of the molding die 12.
In the cavity 12b, the molten aluminum and the magnesium nitrogen compound react on the surface of the cavity 12b, and the magnesium nitrogen compound removes oxygen from the oxide film on the surface of the molten aluminum and reduces it to pure aluminum. The oxygen remaining in the cavity 12b and the oxygen mixed in the aluminum melt become magnesium oxide or magnesium hydroxide and are taken into the melt. Since these magnesium oxides and the like are small amounts and stable compounds, they do not adversely affect the quality of aluminum castings.
[0030]
As described above, also in the case of the casting apparatus 10 shown in FIG. 2, the inside of the cavity 12b is dehumidified and the magnesium nitrogen compound as the reducing compound is introduced, so that the reducing property of the magnesium nitrogen compound is not impaired. The oxide film formed on the surface of the molten metal can be reliably reduced, and the surface of the molten metal can be suitably cast as pure aluminum. Thereby, it is possible to improve the wettability, fluidity, and flowability of the aluminum melt in the cavity 12b, to obtain a high-quality cast product having excellent transferability to the inner wall surface of the cavity 12b and no wrinkles or the like. Will be possible. Instead of sending a dry gas such as nitrogen gas into the cavity, the environment in which the casting apparatus is installed may be used as a dehumidifying environment, whereby the humidity in the cavity may be reduced to 70% or less. .
[0031]
【The invention's effect】
According to the reduction casting method according to the present invention, as described above, the reducing compound is introduced into the cavity in a state where the cavity of the mold is previously dehumidified, or the reducing compound is generated in the cavity. Thereby, it is possible to suppress the reducing compound from reacting with the water in the cavity, and it is possible to reliably maintain the reducing property of the reducing compound, and to perform a suitable reduction casting.
In addition, by using magnesium gas as the metal gas and nitrogen gas as the reactive gas, it is possible to obtain a remarkable effect that it can be suitably used for casting aluminum.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration example of a casting apparatus for casting by applying a reduction casting method according to the present invention.
FIG. 2 is an explanatory view showing another example of the configuration of a casting apparatus for casting by applying the reduction casting method according to the present invention.
FIG. 3 is a graph showing how the reactivity of a reducing compound changes with humidity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Casting apparatus 12 Mold 12a Gate 12b Cavity 12c Metal gas inlet 12d Nitrogen gas inlet 15 Pouring tank 16 Hot water unit 18 Air cylinder 19 Argon gas cylinder 20 Nitrogen gas cylinder 25 Exhaust hole 28 Heating furnace 36 Tank 50 Molten metal

Claims (7)

In a reduction casting method, a molten metal is poured into a cavity of a mold, and the molten metal is brought into contact with the reducing compound in the cavity of the mold to reduce the oxide film formed on the surface of the molten metal and cast.
At least after the humidity in the cavity is 70% or less,
Introducing a reducing compound into the cavity,
Next, the molten metal is poured into a cavity and cast. 2. The reduction casting method according to claim 1, wherein a dry gas that does not react with the reducing compound is introduced into the cavity to dehumidify the cavity, and then the reducing compound is introduced into the cavity. 3. The reduction casting method according to claim 1 or 2, wherein a molten metal of aluminum or an alloy thereof is used as the molten metal, and magnesium nitrogen gas is introduced as a reducing compound into the mold to perform casting. In a reduction casting method, a molten metal is poured into a cavity of a mold, and the molten metal is brought into contact with the reducing compound in the cavity of the mold to reduce the oxide film formed on the surface of the molten metal and cast.
At least after the humidity in the cavity is 70% or less,
The reducing compound is generated in the cavity by introducing a metal gas and a reactive gas into the cavity,
Next, the molten metal is poured into a cavity and cast. After introducing a dry gas that does not react with the reducing compound into the cavity and dehumidifying the inside of the cavity, introducing a metal gas and a reactive gas into the cavity to generate a reducing compound within the cavity. The reduction casting method according to claim 4, wherein The reduction casting method according to claim 5, wherein a reactive gas is used as the drying gas. Using aluminum or its alloy as the molten metal, introducing magnesium gas as the metal gas and nitrogen gas as the reactive gas into the mold to produce a reducing compound in the cavity and casting. The reduction casting method according to claim 4, 5 or 6, wherein:

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