JP2003275857A - Low-pressure casting method for grain dispersion aluminum alloy material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high quality cast product having uniformly dispersed grains therein by uniformly dispersing ceramic grains in molten metal, in a low pressure casting method for aluminum alloy having dispersed ceramic grains. <P>SOLUTION: In the low pressure casting method which introduces the molten metal into a sprue in a metallic mold through a stoke by pressing, a casting apparatus with a gas introducing passage with a valve for introducing the gas into the inner part of the sprue in the metallic mold from the outer part, is used and the molten metal in the stoke is once pushed out into a molten metal holding vessel from the lower part of this stoke by introducing pressing gas from the gas introducing passage while maintaining airtightness in the metallic mold before pouring the molten metal. Thereafter, the molten metal is poured into the metallic mold through the stoke by closing the valve in the gas introducing passage and also, cast while exhausting the gas in the metallic mold through and exhausting passage, such as a vent hole, arranged in the metallic mold. It is preferable that inert gas is used as pressure gas and preheated to 500-700°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low pressure casting method for a particle-dispersed alloy material such as an aluminum alloy having ceramic particles dispersed therein.

[0002]

2. Description of the Related Art Casting products of aluminum alloys in which ceramic particles (particle size: 3 to 50 microns) are dispersed are widely used as mechanical parts such as brake discs and structural parts. The conventional method generally used as a casting method for this kind of aluminum alloy is gravity casting, which is a method in which the molten metal is stirred in a melting furnace or a holding furnace, scooped with a ladle to take out the molten metal, and casting.

By the way, in the aluminum-based particle-dispersed alloy material, since the dispersed particles and the alloy have different specific gravities, the particles are precipitated or floated when left standing. Therefore, in the conventional gravity casting method, the molten metal is stirred in a melting furnace or a holding furnace and scooped with a ladle to take out the molten metal. Also,
In the case of the low pressure casting method, the amount of particles may vary depending on the location. Especially when the casting operation is stopped for a long time, in the case of a material whose specific gravity is heavier than the alloy, a part where no particles exist is generated. There was a problem.

[0004]

In general, particles have a specific gravity different from that of alloys, and therefore, if they are not stirred, they will float or precipitate to separate. Therefore, conventionally, when performing low pressure casting with a particle dispersion strengthened alloy material, the holding furnace is agitated by a stirrer to evenly disperse particles with different specific gravities, but in a stoke that does not reach stirring , Particle precipitation or floating separation occurred. Further, when the specific gravity of the particles was larger than that of the molten alloy, the amount of particles in the molten metal remaining in the holding furnace after the low pressure casting was larger than the predetermined amount. Furthermore, in the product in which the low pressure casting was once interrupted and then cast again, there was a particle missing portion where no particles existed. An object of the present invention is to solve the above-mentioned problems in the conventional low pressure casting method.

[0005]

In order to solve the above problems, the present invention provides the following method. That is, the low-pressure casting method of the particle-dispersed aluminum alloy material according to the present invention is a low-pressure casting method in which the molten metal is introduced into the gate of the mold through stalk by pressurizing the melt, and a gas is introduced from the outside into the gate of the mold. Using a casting device provided with a gas introduction path with a valve, by introducing a pressurized gas from the gas introduction path while maintaining the airtightness of the mold before pouring, the molten metal in the stalk is moved to the lower end of the stalk. After extruding once into the molten metal holding container, the valve of the gas introduction path is closed, the molten metal is poured into the mold through the stalk, and the gas in the mold is vented to the mold. It is characterized by casting while discharging through the exhaust passage.

The gas introduced from the outside is nitrogen gas,
It is preferable to use an inert gas such as argon gas. Further, this gas is preferably heated in advance to a high temperature (for example, 500 to 700 ° C.) in order to prevent the molten metal from being cooled. The pressure of this gas is set so that the molten metal in the stalk is pushed down to the lower end of the stalk.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. FIG. 1 is a vertical cross-sectional view showing an example of a low-pressure casting apparatus of the present invention. This low-pressure casting apparatus 100 includes a die 1 composed of an upper die 1a and a lower die 1b, a crucible 3, an outer casing 4 and a heater 10. The holding furnace configured by A spout 2 is provided on the lower die 1b. On the other hand, the crucible 3 of the holding furnace containing the particle-dispersed aluminum alloy melt M is housed in an outer box 4, and a stalk 5 is inserted in the melt.

A flange 4b is provided on the upper end of the rising portion 4a of the outer box 4, and a through hole 30a having the same diameter as the inner diameter of the stalk 5 is formed in the center between the flange 4b and the lower mold 1b.
The ring member 30 provided with is provided. The upper end of the stalk 5 is attached to the ring member 30 by the packing 7
And the packing 7 is also interposed between the ring member 30 and the lower mold 1b.

On the other hand, a seal packing 27 is provided on the mating surface of the upper die 1a and the lower die 1b of the die 1, and the upper die 1a.
There are provided a plurality of vent holes 40 facing the cavity and a plurality of exhaust pipes 42 communicating from the vent holes to the outside of the mold. The plurality of exhaust pipes 42 are aggregated into one exhaust main pipe 43, and an exhaust valve 45 is provided in the exhaust main pipe 43. Vent hole 40
Is a known one that is usually provided for discharging the air remaining in the mold during pouring.

A heater 10 for heating the molten metal is provided around the crucible 3 in the outer box 4, and a stirring blade 12 of a stirring device 11 with an electric motor is inserted in the crucible 3. The outer box 4 is provided with a pipe 15 with a valve 15a for supplying compressed gas for pressurization (air in the illustrated example) and an exhaust pipe 16 with a valve 16a for exhausting the gas in the outer box. These crucible 3, outer case 4, heater 10, etc.
Configure a holding furnace.

The low pressure casting apparatus 100 includes the mold 1
The ring member 30 between the gate 2 and the stalk 5 is provided with a gas passage 20 to which a pipe 21 from an external inert gas source (not shown) is connected. The pipe 21 is provided with a valve 21a for opening and closing the pipe. The gas passage 20 serves as a passage for a gas that introduces an inert gas from the outside into the vicinity of the sprue. The gas passage 20 is provided with a valve 22 that opens and closes the passage. Valve 2
In the illustrated example, 2 is opened and closed by expansion and contraction of the pneumatic cylinder 25, and the tip end surface is flush with the inner surface of the sprue 2 of the lower mold 1b in the closed state, and in the open state, it projects into the sprue 2 and its circle A gap is formed between the peripheral portion and the inner wall of the gas passage 20. The valve 22 is provided at the tip of a rod connected to the pneumatic cylinder, and is moved back and forth by the cylinder to open and close the gas passage. However, this valve may be opened or closed electrically or hydraulically. .

When casting a particle-dispersed aluminum alloy using this low-pressure casting apparatus, the exhaust valve 16a is closed and the pressurizing valve 15a is opened while the molten metal M in the crucible 3 is agitated and equalized. , Compressed air is supplied into the outer box 4. At this time, the exhaust valve 45 is left open. When the compressed air is supplied, the molten metal in the crucible 3 is pressurized, so that the molten metal rises through the stalk 5 and is introduced into the mold 1. At this time, since the gas passage 20 for supplying the inert gas is closed by the valve 22, the molten metal does not enter the gas passage. Similar to the above-mentioned conventional technique, the pressure is highest and the molten metal is solidified in the mold.

When the solidification is completed, the pressurizing valve 15a is closed to stop the pressurization by the compressed air, and the exhaust valve 16a is opened to release the pressure. Then, a negative pressure is generated in the vicinity of the sprue, and outside air enters through the gap of the packing 7 or the like.
The molten metal therein gradually descends and is separated from the cast molded product. The cast product from which the molten metal has separated is raised from the upper mold 1a and taken out of the mold, and the casting process is started.

In the present invention, when the previous casting is completed and the next casting is started, the pressurized gas is introduced from the outside through the gas passage 20 to the vicinity of the gate. At this time, the valve 45 of the exhaust pipe of the mold is closed and kept in a sealed state. With this pressurized gas, as shown in FIG. 2, the molten metal in the stalk 5 is pushed down to the lower end of the stalk 5, and is pushed out into the crucible 3. Since the molten metal in the crucible 3 is agitated by the agitation blade 12, the extruded molten metal is also subjected to the agitating effect, and the particles are evenly dispersed. After maintaining this state for a predetermined time (several seconds to several tens of seconds), when the valve 21 of the gas passage 20 is closed and the valve 45 of the exhaust pipe is opened, the gas in the stalk 5 is exhausted through the mold. The molten metal in the crucible 3 enters the stalk 5 again and is introduced into the mold through the stalk 5. The valve 45 of the exhaust pipe is closed only when the pressurized gas is introduced, and is always opened. Also, opening the valve 22 for pressurized gas is
Only when introducing pressurized gas, keep closed at other times.

Since the molten metal for the next casting is the one stirred in the crucible 3, the particles are evenly dispersed.
Therefore, it is possible to obtain a high-quality cast product in which particles are evenly dispersed. In the conventional low-pressure casting method, the molten metal remains in the stoke 5 where the stirring effect does not reach even after the previous casting is completed, and is introduced into the mold in the next casting as it is,
Although problems such as particle omission occurred, in the present invention, as described above, since the molten metal in the stalk 5 is once pushed into the crucible after completion of one casting, a uniform particle dispersion state is obtained due to the stirring effect. Is obtained.

Next, FIG. 3 shows an embodiment slightly different from the above. In this embodiment, the vent hole 40 and the exhaust pipes 42 and 43 as described above are not provided, and the gap 47 between the mating surfaces of the split molds is used. The air in the mold is exhausted through. In this method, if the gap 47 between the molds is too large, the pressurized gas escapes from there and a sufficient pressure effect cannot be obtained, so it is preferable to make the gap as small as possible.
If possible, it is desirable to change to the venthole method.
Other parts are the same as those in the above embodiment.

FIG. 4 shows a further different embodiment. This embodiment is an example in which the vent hole 40 is provided in a split type. In this case, the divided surfaces of the mold are partially brought into close contact with each other so that there is no gap communicating with the outside at this portion 48. Other parts are the same as above.

Further, the valve 2 provided at the sprue part
2 and the pressurized gas passage 20 may not be provided, and the pressurized gas may be introduced from the outside through the vent hole 40, the exhaust pipe 42, etc. provided in the mold. In any case, this pressurized gas may be one that can push out most of the molten metal in the stalk into the crucible after casting.

From the standpoint of preventing oxidation, it is preferable to use an inert gas such as nitrogen gas or argon gas as the pressurized gas. Further, it is preferable that the pressurized gas is preheated to 500 to 700 ° C. so as not to cool the molten metal. Furthermore, it is preferable that the pressure of the pressurized gas is set to a pressure corresponding to the differential pressure with which the molten metal in the stalk 5 can be pushed out. In the above description, the entire amount of the molten metal in the stalk 5 is extruded each time casting is completed, but a small amount of the molten metal may remain in the stalk depending on the case. Further, when the casting cycle is short, it is not always necessary to extrude the molten metal in the stalk with the pressurized gas each time one casting is performed, and the molten metal may be extruded once in every two or more castings.

[0020]

As described above, according to the present invention, the molten metal remaining in the stalk after the previous casting is once extruded into the stirring crucible and then introduced again into the stalk to perform casting. Therefore, it is possible to maintain the dispersed state of the particles in a good condition, and it is possible to prevent the generation of defective products such as missing particles.

[Brief description of drawings]

FIG. 1 is a sectional view showing a low pressure casting apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a state where molten metal in a stalk is extruded.

FIG. 3 is a sectional view showing a low pressure casting apparatus different from the above.

FIG. 4 is a sectional view showing still another low-pressure casting apparatus.

[Explanation of symbols]

1 mold 2 gate 3 crucible 4 outer box 5 Stoke 12 stirring blades 20 Gas passage for pressurization 22 Pressurized gas valve 30 Ring member 100 low pressure casting equipment 200 Low pressure casting equipment 300 low pressure casting equipment

Claims (5)

[Claims] 1. A low pressure casting method in which molten metal is introduced into a gate of a mold through a stalk by pressurizing the molten metal, and a casting apparatus provided with a gas inlet passage with a valve for introducing gas from the outside into the gate of the die. Using, by introducing a pressurized gas from the gas introduction path in a state of maintaining the airtightness of the mold before pouring, once the molten metal in the stalk is extruded from the lower end of the stalk into the molten metal holding container, The valve of the gas introduction path is closed, the molten metal is poured into the mold through a stalk, and the gas in the mold is discharged while being discharged through an exhaust passage such as a vent hole provided in the mold. Low-pressure casting method for particle-dispersed aluminum alloy materials. 2. The exhaust passage is a plurality of vent holes,
Each of the vent holes is connected to a pipe, and a valve that opens and closes all the pipes is provided at a place where these pipes are gathered. A packing that keeps the mold airtight is provided on the mating surface of the mold. The low pressure casting method of the particle-dispersed aluminum alloy material according to claim 1. 3. The low pressure casting method for a particle-dispersed aluminum alloy material according to claim 1, wherein the gas introduced from the outside is an inert gas. 4. The low pressure casting method for a particle-dispersed aluminum alloy material according to claim 1, wherein the gas introduced from the outside is heated. 5. The particle-dispersed aluminum alloy material according to claim 1, wherein the pressure of the gas introduced from the outside is set so that the molten metal in the stalk is pushed down to the lower end of the stalk. Low pressure casting method.