JP3589615B2 - Reduction casting method and reduction casting mold - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reduction casting method and a reduction casting mold, and more particularly to a reduction casting method and a reduction casting mold for casting while reducing an oxide film on a molten metal surface with a reducing compound.
[0002]
[Prior art]
Among the casting methods, aluminum casting methods include gravity casting (GDC), low pressure casting (LPDC), die casting (DC), squeeze (SC), and thixomold. In each of these casting methods, a molten aluminum is poured into a cavity of a mold to perform casting.
In general, aluminum or an alloy thereof has a property of easily forming an oxide film. Therefore, in the aluminum casting process, an oxide film is easily formed on the surface of a molten aluminum. As a result, the surface tension of the molten aluminum increases, and the fluidity, melting and welding properties of the molten aluminum decrease, and various casting defects occur. For this reason, various improvements and techniques have been studied regarding the use of a mold coating agent, a method for injecting a molten metal into a mold, and an injection speed and pressure for injecting the molten metal.
[0003]
For example, in the area of GDC or LPDC, a method of applying an adiabatic release agent, a method of arranging a gate, and the like in a GDC or LPDC region as a countermeasure against a molten metal run-out due to the growth of an oxide film formed on a molten metal surface, a hot water wrinkle, a hot water boundary, and the like. In addition, in the DC region, high-pressure short-time filling is performed by the filling speed, pressure, gate arrangement, overflow taking, etc. of the aluminum melt in the DC area. ing. In the area of SC or the like, the oxide film on the surface of the molten aluminum is forcibly destroyed and fused by applying high pressure in the area of GDC.
[0004]
However, the conventional aluminum casting method has advantages and disadvantages, and in particular, it is extremely difficult to eliminate hot water wrinkles, hot water boundaries and minute unfilling that occur in cast products due to the oxide film on the surface of the molten aluminum. there were. For this reason, among aluminum castings, aluminum products that are problematic in surface stress, notch, etc., especially aluminum structures used in aircraft, automobiles, etc., have variations in reliability, and therefore, fluorescent A 100% inspection by flaw detection or the like, or an aluminum cast product obtained by casting is subjected to surface processing to be a final product, which has led to an increase in cost of the aluminum product.
The inventor of the present invention has previously disclosed Japanese Patent Application No. 11-91445 in order to eliminate wrinkles and the like of a cast product caused by an oxide film on the surface of a molten metal, which was difficult to solve by such a conventional casting method. In the specification, a reduction casting method is proposed in which an oxide film on a surface of a molten aluminum injected into a cavity of a mold is reduced and cast by a reducing compound generated by a reaction between a metal gas and a reactive gas. did.
[0005]
[Problems to be solved by the invention]
According to the reduction casting method proposed earlier by the present inventors, the reducing compound present in the cavity of the mold deprives the oxide film on the surface of the molten aluminum of oxygen of pure aluminum, resulting in pure aluminum. The surface tension can be reduced to improve the fluidity, the hot-dipability, and the wettability with the inner wall surface of the cavity, and the wrinkles and the like generated due to the oxide film can be eliminated. .
However, in the reduction casting method proposed earlier, a reducing compound generated by previously reacting a metal gas and a reactive gas in a reaction tank provided outside the mold is injected into the cavity. For this reason, it turned out that the supply pipe for supplying the reducing compound from the reaction tank into the cavity is easily blocked by the reducing compound, and the casting efficiency tends to be reduced due to the cleaning of the closed supply pipe.
Accordingly, an object of the present invention is to provide a reduction casting method and a casting method capable of preventing a supply pipe into a cavity from being clogged and improving casting efficiency when casting while reducing an oxide film on a molten metal surface with a reducing compound. An object of the present invention is to provide a reduction casting mold.
[0006]
[Means for Solving the Problems]
As a result of repeated investigations to solve the above-described problems, the present inventors separately supply a metal gas and a reactive gas into a cavity of a mold, and react the two in the cavity to generate a reducing compound. Thus, the present inventors have found that the blockage of the supply pipe into the cavity can be prevented, and arrived at the present invention.
That is, according to the present invention, when casting a cast product by injecting a molten metal into a mold cavity, a metal compound and a reactive gas are reacted in the cavity of the mold to generate a reducing compound. In order to achieve this, the mold has a molten metal injection hole for injecting molten metal into the cavity, a metal gas injection hole for injecting the metal gas, and a gas injection hole for injecting the reactive gas. Using a metal gas injected into the cavity from each of the metal gas injection hole and the gas injection hole and a reactive gas to generate a reducing compound, the reducing compound adheres to the inner wall surface Wherein the molten metal is injected into the cavity through the molten metal injection hole, and casting is performed while reducing an oxide film on the surface of the molten metal with a reducing compound.
Further, the present invention is directed to a reduction casting for reducing and casting an oxide film on a surface of a molten metal injected into the cavity by a reducing compound generated by a reaction between a metal gas and a reactive gas injected into the cavity. the die, the molten metal injection hole for injecting the dissolved water in the cavity, the metal gas injection hole for injecting the metal gas, and the gas injection holes for injecting the reactive gases, formed individually on the mold It is also a molding die for reduction casting characterized by being performed.
[0007]
In the present invention, by exposing the metal material forming the mold to the inner wall surface of the cavity, the inner wall surface of the cavity can be made substantially non-reactive with the reducing compound, and before the injection of the molten metal. A situation in which the reducing compound is oxidized or the like can be prevented. Similarly, when injecting each of the metal gas and the reactive gas into the cavity, the inside of the cavity is made substantially a non-oxygen atmosphere. Can be prevented.
By using gaseous magnesium and nitrogen gas as such a metal gas and a reactive gas and generating a magnesium nitrogen compound (Mg ₃ N ₂ ) as a reducing compound, the handling of the metal gas and the reactive gas is facilitated. be able to.
Also, by connecting the metal gas injection hole to a metal gas generator that generates a metal gas, the metal gas can be easily injected into the cavity of the mold.
Further, the metal gas injection hole and / or the gas injection hole can also serve as the discharge hole for discharging the gas in the cavity when the molten aluminum is injected into the cavity, thereby forming a new discharge hole. The molten aluminum can be easily injected into the cavity without forming the mold.
In the present invention, the term “aluminum” includes not only pure aluminum but also an aluminum alloy containing aluminum as a base material, for example, silicon, magnesium, copper, nickel, tin, or the like.
[0008]
The reducing compound employed in the present invention, which is a reaction product of a metal gas and a reactive gas, is usually difficult to exist in the form as it is in the atmosphere. Not fully clarified.
In this regard, in the present invention, the metal gas and the reactive gas, which can exist in the form as they are even in the atmosphere, are supplied into the cavity of the mold via separate paths and injection holes, and are reacted in the cavity to reduce The compound is produced. For this reason, it is possible to prevent the supply pipes of the metal gas and the reactive gas from being clogged by using a metal gas and a reactive gas for which measures to block the supply pipes are known or which may not be required. As a result, a decrease in casting efficiency due to blockage of the supply pipe into the cavity of the molding die can be prevented, and casting efficiency can be improved.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
An example in which the reduction casting method according to the present invention is applied to an aluminum casting method will be described. FIG. 1 shows an example of a casting apparatus for carrying out such an aluminum casting method. A molding die 12 provided in the casting apparatus 10 shown in FIG. 1 is connected to a pouring tank 14 in which a molten aluminum 18 is stored, and has a molten metal injection hole 11 in which the molten aluminum 18 is poured into a cavity 12a. ing.
A tenon 16 is inserted into the molten metal injection hole 11 so as to be movable in the vertical direction. By pulling up the tenon 16, a required amount of aluminum molten metal 18 is poured from the pouring tank 14 into the cavity 12 a.
In the molding die 12 shown in FIG. 1, an inner wall surface of the cavity 12a is formed by exposing a metal surface of a metal forming the molding die 12.
[0010]
The molding die 12 is connected to the nitrogen gas cylinder 20 by a pipe 22, and by opening a valve 24, a nitrogen gas as a reactive gas is injected into the cavity 12 a and the interior of the cavity 12 a is substantially changed to a nitrogen gas atmosphere. A non-oxygen atmosphere can be used.
The argon gas cylinder 25 is connected to a heating furnace 28 as a generator for generating a metal gas through a pipe 26, and the argon gas can be injected into the heating furnace 28 by opening a valve 30. 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 more at which magnesium powder sublimates in order to generate magnesium gas as a metal gas described later.
[0011]
The argon gas cylinder 25 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. I have. This pipe 38 is also provided with a valve 40. The heating furnace 28 is connected to the cavity 12 a of the mold 12 through a pipe 44 that penetrates the pipe 42 and the tenon 16 and communicates with the cavity of the mold 12. The pipe 42 is provided with a valve 45.
Further, a pressure reducing pipe 17 connected to a vacuum generator (not shown) such as a vacuum pump is connected to the cavity 12a of the mold 12 so as to reduce the pressure inside the cavity 12a. The pressure reducing pipe 17 is also provided with a valve 19.
[0012]
As shown in FIG. 1, the mold 12 has a metal gas injection hole 44a for injecting a magnesium gas into the cavity 12a, a nitrogen gas in the cavity 12a, in addition to the molten metal injection hole 11 into which the molten aluminum 18 is poured. And a pressure reducing hole 17a for reducing the pressure inside the cavity 12a. By using one of the holes as an exhaust hole for exhausting the gas in the cavity 12 when the molten aluminum 18 is poured into the cavity 12a, the molten aluminum 18 can be smoothly poured. it can. The hole that also serves as the exhaust hole is preferably one of the metal gas injection hole 44a and the nitrogen gas injection hole 22a, and it is particularly preferable that the nitrogen gas injection hole 22a also serves as the exhaust hole. .
FIGS. 2A and 2B show the structure of the nitrogen gas injection hole 22a and the decompression hole 17a. As shown in FIG. 2 (a), the connection ports 13 of these holes are formed as tapered holes that extend outward on the outer wall of the molding die 12, and a connection plug ( (Not shown) is detachably contacted. The connection port 13 communicates with the cavity 12a through the passages 15, 15,... Shown in FIG.
[0013]
In the present invention, the molding die 12 shown in FIG. 3A can be used instead of the molding die 12 shown in FIG. In the mold 12 shown in FIG. 3A, a tenon 16 is inserted movably in a vertical direction into a molten metal inlet 11a constituting a molten metal injection hole 11 into which a molten aluminum 18 is poured into a cavity 12a. . The The water inlet 11a and the cavity 12a is communicated with the water injection passage 11b, by raising the tenon (plug) 16, molten aluminum 18 in the molten metal bath 14, hot water inlet 11a or et water injection path 11b And is injected into the cavity 12a. A metal gas injection hole 44a is connected in the middle of the hot water injection path 11b.
Further, headers 23a and 23b are formed in the molding die 12 with the cavity 12a interposed therebetween, and a nitrogen gas injection hole 22a for injecting nitrogen gas into the cavity 12a and / or a decompression hole 17a are connected to the headers 23a and 23b. ing. The headers 23a, 23b and the cavity 12a are connected by passages 15, 15,... Shown in FIG.
In the mold 12 shown in FIG. 3A, the metal gas injection hole 44a, the nitrogen gas injection hole 22a, and one of the pressure reducing holes 17a are used for pouring the molten aluminum 18 into the cavity 12a. It is preferable that the function of an exhaust hole for exhausting gas in the cavity 12 is also used, and it is particularly preferable that the nitrogen gas injection hole 22a also serves as an exhaust hole.
When the molten aluminum 18 is poured into the cavity 12a, an exhaust hole for exhausting the gas in the cavity 12 may be newly formed in the molding die 12.
[0014]
When performing aluminum casting by the casting apparatus 10 shown in FIG. 1, first, the valve 24 is opened, nitrogen gas is injected into the cavity 12 a of the mold 12 from the nitrogen gas cylinder 20 via the pipe 22, Purge air with nitrogen gas. The air in the cavity 12a is discharged from an air vent hole (not shown) in the upper part of the mold, and the inside of the cavity 12a can be made to have a nitrogen gas atmosphere and a substantially non-oxygen atmosphere. Thereafter, the valve 24 is closed once.
[0015]
While the air in the cavity 12a of the molding die 12 is being purged, the valve 30 is opened and an argon gas is injected into the heating furnace 28 from the argon gas cylinder 20 to make the inside of the heating furnace 28 oxygen-free.
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. The heating furnace 28 is heated by the heater 32 to a furnace temperature of 800 ° C. or higher at which the magnesium powder sublimes. For this reason, the magnesium powder sent into 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 magnesium gas is injected into the cavity 12a through the pipes 42 and 44 while adjusting the argon gas pressure and the flow rate.
After injecting the magnesium gas into the cavity 12a, the valve 45 is closed and the valve 24 is opened to inject the nitrogen gas into the mold. As described above, by injecting the nitrogen gas into the molding die 12, the magnesium gas and the nitrogen gas react in the cavity 12a to generate a magnesium nitrogen compound (Mg ₃ N ₂ ). This magnesium nitrogen compound precipitates as a powder on the inner wall surface of the cavity 12a.
When the nitrogen gas is injected into the cavity 12a, the pressure and the flow rate of the nitrogen gas are appropriately adjusted. It is also preferable to inject the nitrogen gas by preheating so that the nitrogen gas and the magnesium gas react easily 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.
[0017]
Here, the magnesium nitrogen compound is a reducing compound, and if oxygen is present in the cavity 12a, it is oxidized to magnesium oxide (MgO), so it is important to discharge oxygen in the cavity 12a as much as possible. It is.
For this reason, when purging the air in the cavity 12a, a vacuum generating device such as a vacuum pump is driven to open the valve 19, and the inside of the cavity 12a is depressurized through the depressurizing pipe 17, and then the valve 19 is turned on. After closing, it is preferable to inject nitrogen gas into the cavity 12a of the mold 12 by opening the valve 24.
In addition, the magnesium nitrogen compound generated in the cavity 12a often floats in the cavity 12a in the form of fine particles. For this reason, it is also preferable that the magnesium nitrogen compound be positively adhered to the inner wall surface of the cavity 12a by opening the valve 19 again and reducing the pressure inside the cavity 12a through the pressure reducing pipe 17.
[0018]
With the magnesium nitrogen compound attached to the inner wall surface of the cavity 12a, the tenon 16 is pulled up, and the molten aluminum 18 in the pouring tank 14 is injected into the cavity 12a.
The molten aluminum poured into the cavity 12a comes into contact with the magnesium-nitrogen compound attached to the inner wall surface of the cavity 12a, and the magnesium-nitrogen compound deprives the oxide film on the surface of the molten aluminum of oxygen of the molten aluminum. The surface is reduced to pure aluminum.
Oxygen remaining in the cavity 12a 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 produced in this manner are small and stable compounds and do not adversely affect the quality of the resulting aluminum casting.
[0019]
As described above, since the magnesium nitrogen compound removes oxygen from the oxide film on the surface of the molten aluminum to form pure aluminum, casting can be performed without forming an oxide film on the surface of the molten metal. For this reason, it is possible to prevent the surface tension of the molten aluminum from increasing due to the oxide film during the casting process, and it is possible to improve the wettability, fluidity, and flowability of the molten aluminum. As a result, it is possible to obtain a good aluminum cast product which is excellent in the transferability (smoothness) determined with the inner wall surface of the cavity 12a and does not cause hot water wrinkles or the like.
[0020]
In the present invention, it is necessary that the magnesium nitrogen compound attached to the surface of the cavity 12a of the mold 12 has a reducing property. Therefore, the metal material forming the mold 12 is exposed on the inner wall surface of the cavity 12a of the mold 12 shown in FIGS. Usually, the metal material forming the mold 12 is non-reactive with the magnesium nitrogen compound generated in the cavity 12a in the temperature range of the aluminum casting process.
Here, when an oxide-based heat-insulating agent or mold release agent, which is generally used as a treatment of the inner wall surface of the cavity, is applied to the inner wall surface of the cavity 12a during aluminum casting, magnesium The nitrogen compound reacts with an oxygen group such as a heat insulating agent and loses a reducing function. For this reason, the inner wall surface of the cavity 12a is formed of a material that is non-reactive with a reducing compound such as a magnesium nitrogen compound.
Therefore, when coating the inner wall surface of the cavity 12a of the molding die 12, it is preferable to coat with a non-oxide material such as graphite. Further, the inner wall surface of the cavity 12 which has been subjected to a heat treatment (forming process of iron tetroxide) or a nitriding treatment may be used.
[0021]
In the above description, nitrogen gas is injected into the cavity 12a from the nitrogen gas cylinder 20 in order to purge air in the cavity 12a of the molding die 12, but purged with an inert gas such as argon gas instead of nitrogen gas. May be.
In this case, when the argon gas is injected into the heating furnace 28 and the inside of the heating furnace 28 is made oxygen-free, the valve 45 is opened, and the argon gas injected into the heating furnace 28 is introduced into the cavity 12 a of the mold 12. This can be done by injection.
[0022]
Although the casting apparatus shown in FIGS. 1 and 2 performs aluminum casting by gravity casting, the present invention can be applied to a conventional aluminum casting method. For example, the casting apparatus shown in FIG. 4 performs aluminum casting by a pressure casting method. In the casting apparatus shown in FIG. 4, the forming die 12 includes an upper forming die 50 and a pressing die 51. The molding die 12 shown in FIG. 4 has higher airtightness than the molding die used in the gravity casting method shown in FIGS.
In the casting apparatus 10 shown in FIG. 4, a pipe 53 is branched in the middle of a pipe 22 connecting the nitrogen gas cylinder 20 and the cavity 12a of the molding die 12, and a vacuum pump 52 is connected. A valve 54 is provided in the middle of the pipe 22. Further, the inside and outside of the molding die 12 are connected by a pipe 55, and the pipe 55 is provided with a valve 56.
[0023]
When casting using the casting apparatus 10 shown in FIG. 4, first, the valves 24 and 56 are closed, the valve 54 is opened, and the vacuum pump 52 is driven to reduce the pressure inside the cavity 12a of the mold 12. Due to such reduced pressure, the inside of the cavity 12a can be made substantially non-oxygen.
Further, after injecting argon gas from the argon gas cylinder 25 into the heating furnace 28, the valve 33 is opened to inject argon gas into the tank 36, and the magnesium powder is sent from the tank 36 to the heating furnace 28 to sublime the magnesium powder. Generates magnesium gas. The generated magnesium gas is injected into the cavity 12a of the mold 12 with argon gas by opening the valve 45 with the valves 54 and 56 closed.
Next, the valve 45 is closed, the valves 24 and 54 are opened, and nitrogen gas is injected from the nitrogen gas cylinder 20 into the cavity 12a. In the cavity 12a, the injected magnesium gas reacts with the nitrogen gas, and powder of a magnesium nitrogen compound is generated on the inner wall surface of the cavity 12a.
[0024]
In this manner, the molten aluminum is injected into the cavity 12a by pushing up the pressing mold 51 with the powder of the magnesium nitrogen compound adhered to the inner wall surface of the cavity 12a.
At this time, since the magnesium nitrogen compound adheres to the inner wall surface of the cavity 12a, casting can be performed while preventing an oxide film from being formed on the surface of the molten aluminum by the same action as described above. As a result, a good quality aluminum casting can be obtained.
In the mold 12 shown in FIG. 4, the inner wall surface of the cavity 12a is heat-treated to form a treated film 12b made of iron tetroxide. Since iron tetroxide has no reactivity with the magnesium nitrogen compound, the treatment film 12b does not impair the function of reducing the magnesium nitrogen compound.
As the treatment of the inner wall surface of the cavity 12a, a nitriding treatment can also be mentioned.
Further, in the casting apparatus 10 shown in FIG. 4, at the time of pouring the molten aluminum or at the time of pressure casting, the valve 56 is opened to facilitate the pouring of the molten aluminum.
In the above description, a method of casting aluminum and / or an alloy thereof has been exemplified. However, the present invention is also applicable to a method of casting magnesium, iron, and / or an alloy thereof.
[0025]
【The invention's effect】
According to the present invention, a supply pipe for supplying a metal gas and a reactive gas, which can exist in an intact form in the atmosphere, into a cavity of a molding die via separate paths and injection holes, and supplying the supply gas into the cavity. As a result of preventing the blockage, aluminum casting can be continuously performed for a long time, and aluminum casting can be industrially performed.
Moreover, since the obtained aluminum casting has extremely few defects such as hot water wrinkles, hot water borders and minute unfilled, the reliability of the aluminum product can be improved, and the aluminum product used in aircraft, automobiles and the like can be used. Inspection and the like of the structure can be eliminated or simplified.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a casting apparatus used in a reduction casting method according to the present invention.
FIG. 2 is a partial cross-sectional view showing a structure of a connection port provided in the molding die shown in FIG.
FIG. 3 is a cross-sectional view and a partial cross-sectional view showing another example of the mold shown in FIG.
FIG. 4 is a schematic view showing another example of a casting apparatus employed in the reduction casting method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Casting apparatus 12 Mold 12a Cavity 12b Treatment film 14 Pouring tank 17a Decompression hole 18 Aluminum melt 20 Nitrogen gas cylinder 22a Nitrogen gas injection hole 25 Argon gas cylinder 28 Heating furnace 32, 32a Heater 36 Tank 44 Pipe 44a Metal gas injection hole 50 Forming Mold 51 Press molding mold 52 Vacuum pump

Claims (8)

When casting a cast product by injecting a molten metal into the cavity of the mold,
In order to generate a reducing compound by reacting a metal gas and a reactive gas in a cavity of the mold , a metal injection hole for injecting a molten metal into the cavity and a metal for injecting the metal gas are used as the mold. Gas injection holes, and using a mold in which gas injection holes for injecting the reactive gas are individually formed,
After reacting the metal gas and the reactive gas injected into the cavity from each of the metal gas injection hole and the gas injection hole to generate a reducing compound,
A reduction casting method comprising: injecting a molten metal from a molten metal injection hole into a cavity in which the reducing compound is attached to an inner wall surface; and casting while reducing an oxide film on the surface of the molten metal by the reducing compound. 2. The reduction casting method according to claim 1, wherein when injecting each of the metal gas and the reactive gas into the cavity, the interior of the cavity is made substantially a non-oxygen atmosphere. As molten metal, with molten aluminum, and the metal gas and reactive gas, magnesium nitrogen compound as the reducing compound with magnesium gas and the nitrogen gas (Mg ₃ N ₂₎ to generate the first aspect or Item 3. The reduction casting method according to Item 2. A reduction casting mold for reducing and casting an oxide film on the surface of a molten metal injected into the cavity by a reducing compound generated by a reaction between a metal gas and a reactive gas injected into the cavity,
Wherein the molten metal injection hole for injecting the dissolved water in the cavity, the metal gas injection hole for injecting the metal gas and that the gas injection hole for injecting the reactive gas is formed individually on the mold Mold for reduction casting. The mold for reduction casting according to claim 4, wherein the metal gas injection hole is connected to a metal gas generator that generates a metal gas. The mold for reduction casting according to claim 4 or 5, wherein the metal gas injection hole and / or the gas injection hole is also a discharge hole for discharging gas in the cavity when a metal melt is injected into the cavity. . The mold for reduction casting according to any one of claims 5 to 6, wherein a metal material forming the mold is exposed on an inner wall surface of the cavity. The molten metal injection hole for injecting the molten metal into the cavity is a molten metal injection hole for injecting the molten aluminum into the cavity, and the metal gas injection hole for injecting the metal gas is magnesium gas for injecting metal gaseous magnesium. The molding die for reduction casting according to any one of claims 4 to 7, wherein the injection hole and the gas injection hole for injecting the reactive gas are nitrogen gas injection holes for injecting nitrogen gas.

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