JPH0985421A - Reduced pressure casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the fluidity of molten metal and to cast a casting without defect caused by the entrapment of gas by connecting a reduced pressure suction hole with hollow parts communicated with the outer part through core print parts and casting while reducing the pressure in a core and a cavity. SOLUTION: In the core print parts 17 of a permeable mold 1, the hollow parts 10 opened toward a bottom surface are arranged, and in the core 8, core hollow parts 9 communicated with the hollow parts 10 are arranged. It is desirable to execute coating for preventing the suction of the generating gas in the inner surface of the permeable mold 1 forming the cavity. A pressure reducing device 12 has a reduced pressure suction hole 13 closely contacting with a vacuum pump 14, pressure reduced degree control means 15 and the hollow parts 10. The pressure in the cavity is reduced and cast by using these devices to improve the fluidity of the molten metal and to prevent mis-running, cold shut and the defect of surface fold, etc., by removing the generated gas. Therefore, a thin casting having complicate shape can be cast.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cavity, a core,
The present invention relates to a vacuum casting method in which a breathable mold having a gate and a weir is depressurized to be cast, and particularly, castings such as thin stainless cast steel and heat-resistant cast steel having a complicated shape are unwound, melted, blown, and wrinkled. The present invention relates to a reduced-pressure casting method for producing soundly without casting defects.

[0002]

2. Description of the Related Art A thin casting having a wall thickness of 5 mm or less is easily solidified when molten metal is poured and comes into contact with a mold, and even if it is not solidified, the viscosity is large. As a result, the fluidity becomes poor, and it is apt to cause improper rotation and defects in the hot water. Further, when casting a thin-walled casting having a complicated shape, it is particularly easy to entrain gas generated from air or a mold in the molten metal, blown by the casting after solidification, and gas defects such as wrinkles are likely to occur. . Therefore, it has been difficult to cast a thin casting having a complicated shape and a wall thickness of 5 mm or less with a material having a poor fluidity of the molten metal such as stainless cast steel and heat resistant cast steel.

The applicant of the present invention has previously disclosed Japanese Patent Laid-Open No. 59-229257.
As a publication, a vacuum casting mold structure having an embedded core (the core may be hollow or solid) is disclosed.
In this method, the product part mold space (cavity) is depressurized through the mold and through the depressurizing hole and the core provided in the mold. The mold and the product part mold space (cavity) formed in the mold share the boundary, and since the decompression hole is provided in this mold, the product part mold space (cavity) is a gas from the mold. There is a case where the desired decompression effect cannot be expected by freely sucking in.

The applicant of the present invention, in Japanese Patent Laid-Open No. 6-55255, has a sand mold (core embedded) having a cavity, a sprue and a riser or a skein, and a pressure reducing device, and the weir part of the sand mold. With a feeder or skein provided at a position distant from, a hole portion communicating with the outside is provided in the vicinity of the feeder or skein, and the decompression device has a suction port in contact with the hole portion, A method and an apparatus for manufacturing a cast steel cast product by a sand mold in which casting is performed while depressurizing the inside of the cavity by depressurizing from the suction port that is in contact with a hole portion, have been proposed. In this proposal, since the depressurization of the cavity is performed through the riser or the hank, the generated gas is sucked indirectly from the core-embedded cavity. Is
In some cases, the depressurizing effect may be slightly small, and for the shape of the cavity containing the core with such a thin complex shape, further improvement by the direct suction method from the core part was expected.

Therefore, the object of the present invention is to solve the above-mentioned conventional problems and improve the fluidity of the molten metal even in a thin stainless cast steel or heat-resistant cast steel having a complicated shape and partially having a wall thickness of 5 mm or less. It does not turn around
To provide a reduced-pressure casting method capable of producing a sound casting without generating gas defects such as wrinkles by being blown into a casting after solidification by reducing entrainment of gas generated from air or a mold in a molten metal. Is.

[0006]

As a result of earnest research in view of the above-mentioned object, the inventors of the present invention have provided a hole in the core skirting part in a breathable mold, and have a decompressor to remove the hole from the hole. By casting with reduced pressure inside the child and cavity, even in castings such as thin-walled stainless cast steel and heat-resistant cast steel that have a core and have a complicated shape, it is possible to prevent improper rotation, defects in the molten metal, etc. The present invention was conceived in the present invention by finding that a sound casting can be obtained without being blown into a casting after solidification without causing gas defects such as wrinkles.

That is, the vacuum casting method of the present invention is a vacuum casting method in which a molten metal is cast by depressurizing a breathable mold having a cavity, a core, a sprue and a weir, and forming a cavity in the breathable mold. A core is embedded in the part, a hole portion communicating with the outside is provided in the core skirting portion of the core, and a vacuum pump and a pressure reducing suction port of a pressure reducing device having a pressure reducing degree control means are connected to the hole portion. Then, casting is performed while depressurizing the inside of the core and the cavity through the hole portion by the depressurizing device.

Then, a core hollow portion communicating with the hole portion provided in the core skirting portion is provided in the core, and the reduced pressure value of the hole portion is made larger than the reduced pressure value of the sprue casting. To do.
Further, in order to improve the pressure reduction effect of the core and the cavity through the hole portion by blocking gas suction from the breathable mold, the core skirting portion in which the hole portion is formed. A gas suction prevention coating layer is formed on the outer surface of the. This gas suction preventing coating layer is a 0.1 to 0.
A coating layer having a thickness of 4 mm, for example, 0.2 mm is formed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A hole part communicating with the outside is provided in a core skirting part in a breathable mold, and a vacuum pump and a pressure reducing suction port of a pressure reducing device having a pressure reducing degree control means are connected to the hole part. Let
By depressurizing the core and the cavity through the pores with the depressurizing device and casting, a thin casting of complicated shape partially having a wall thickness of 5 mm or less cannot be turned around, and there are defects in the water level, blown, and molten metal. It is possible to secure a pressure gradient in the cavity and a molten metal injection speed for casting as a sound casting without generating wrinkles, and particularly, it is possible to effectively remove air or gas generated from the mold so as not to be caught in the molten metal.

By providing the core hollow portion communicating with the holes provided in the core skirting portion in the core, the effect of removing the generated gas can be further enhanced.

When the depressurized value of the hole is made larger than the depressurized value of the sprue, the fluidity of the molten metal is secured without disturbing the flow of the molten metal, and the suction casting effect of the molten metal to the thin portion of the cavity is improved. The pressure reduction value can be adjusted by changing the rotation speed of the vacuum pump by operating the pressure reduction degree control means.

Further, the vacuum suction is performed by a transfer device (not shown).
When the breathable mold is transported and positioned by the above method, the pressure is suctioned by the depressurizing device through the pores opened toward the outer surface of the breathable mold.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an embodiment of the present invention and is a vertical cross-sectional view showing a vacuum casting apparatus for two pieces. The vacuum casting apparatus used in the present invention comprises a breathable mold 1 and a vacuum apparatus 12. The decompression device 12 includes a vacuum pump 14
And the opening portion 10a of the hole portion 10 provided in the core skirting portion 17.
16 having a vacuum suction port 13 connected to the
And a decompression degree control means 15 installed between the decompression suction port 13 and the vacuum pump 14.

As shown in FIGS. 2 and 3, the breathable mold 1 has a thin scroll portion (a portion serving as a passage for exhaust gas) 21 having an outer diameter of 120 mm and a thickness of 3.0 mm by a core 8.
Two flange portions 22 having a thickness of 15 mm on the upper and side portions thereof, and a thickness of 20 mm and a height of 2 on the outer peripheral portion of the upper flange
A thin cavity 2 having a complicated shape having two 5 mm boss portions 23 is formed. The breathable mold 1 is a cold box type and uses silica sand No. 6. The sprue 5 is provided near the center of the air-permeable mold 1, and the sprue 5 is provided with a continuous runner 6 and a weir portion 7. The core skirting part 17 of the breathable mold 1 is provided with a hole portion 10 that opens toward the bottom surface, and the core 8 is provided with a core cavity portion 9 that communicates with the hole portion 10. In order to prevent the solid impurities mixed in the molten metal 3 from flowing into the cavity 2 between the runner 6 and the weir 7,
It is preferable to arrange a filter. Further, on the inner surface of the breathable mold 1 that forms the cavity, it is preferable to form a gas suction prevention coating mold by brush coating or spraying in order to prevent the gas generated from the mold from being sucked into the cavity.

As shown in FIG. 1, the hole portion 10 of the core skirting portion 17 of the core 8 embedded in the air permeable mold 1 is perpendicular to the opening 10 a provided on the lower surface of the air permeable mold 1. It extends upward and communicates with the core hole 9. The core hole portion 9 also extends vertically upward, and its tip extends almost to the same position as the upper end portion of the core 8 having the maximum lateral width of the core 8. Therefore, the gas generated from the core 8 can be efficiently sucked and removed.

The decompression device 12 includes a vacuum pump 14, a decompression degree control means 15, and a decompression suction port 13 for adsorbing decompression by bringing the flexible pipe into close contact with the hole portion 10 of the breathable mold 1.
have.

Next, an embodiment of the vacuum casting method for producing a cast steel casting by the above apparatus will be described. FIG.
[Fig. 3] is an external view of a turbine housing 19 of a turbo rotor for an automobile, which is a cast product made of heat-resistant cast steel. Its longitudinal section is shown in FIG.
As shown in, the hollow part 2 of the cast product has a complicated shape.
In order to form 0, as shown in the appearance in FIG. 4, the core 8 embedded in the breathable mold 1 is not a simple shape but a core shape having a spiral portion. By setting the core 8 in a main mold (not shown) of a breathable mold, a thin portion of the cavity 2 (this thin portion is the thin portion 24 of the cast product) is formed around the core 8. To be done. The breathable mold 1 is carried into the pouring station (not shown) by a carrier device. Next, the decompression suction port 13 from the decompression device 12 is brought into close contact with the hole portion 10 of the breathable mold 1. And the hole portion 10
The depressurized value inside is set to be in the range of -100 to -20 mmHg before pouring, and the depressurized value of the hole portion is made larger than that of the sprue. After that, a predetermined amount of molten metal is poured from the ladle 4 into the cavity 2 for casting. The temperature of the molten metal in the ladle 4 is 15
It was set to a range of 00 to 1600 ° C. Table 1 shows the chemical composition of the cast steel.

[0018]

[Table 1]

After the cast steel casting is solidified in the breathable mold 1, it is carried out to the next demolding station (not shown) by the carrying device. Then, another breathable mold 1 before casting is carried into the pouring station. The above steps are repeated to cast the required number of cast steel castings. The quality of the castings was investigated by casting 80 thin-walled cast steel castings having complicated shapes with flanges shown in FIGS. 2 and 3. As a result, the injection speed of the molten metal is high, and the molten metal is less likely to be disturbed, and without entraining air or gas generated from the mold in the molten metal, the total number, the non-rotating state, the water level, the blowing,
There was no casting defect such as wrinkles, and it was sound.

FIG. 5 is a vertical cross-sectional view showing another embodiment in which vacuum suction is performed from the core cavity. The core 8 embedded in the cavity forming portion of the breathable mold (main mold) 1.
A cavity 2 is formed between the outer periphery of the mold and the breathable mold 1. This cast product has a complicated shape, and as shown in FIG. 5, it has ear-shaped thin-walled portions 2 on both sides, and the core 8 embedded to form this thin-walled portion is thick at this portion. Of course, it is thought that the gas generated from the core is large. Therefore, the core hollow part is extended vertically upward from the decompression suction port 13 and its tip is formed so as to reach the vicinity of the ear-shaped part. As a result of performing vacuum suction casting according to this embodiment, a casting defect such as blowing was not generated, and a sound cast product could be obtained.

FIG. 6 is a vertical sectional view showing a comparative embodiment. In this comparative example, the core 8 to be embedded is solid. The reduced-pressure suction was performed by reducing the pressure from the thin-walled cavity portion 2 through the suction member 26, the mold cavity portion 27, the reduced-pressure suction port 13, and the pressure-reducing device 12 (not shown). Even though the suction member 26 is made of a material having better ventilation than the breathable mold 1, the suction member 26 is blown in the vicinity of the thin portion 2 as shown in FIG. Occurred. This is considered to indicate that since the core 8 is solid, it is insufficient to suck and remove the generated gas only from the outer surface of the solid core.

[0022]

As described above in detail, the core skirting part in the air-permeable mold is provided with a hole communicating with the outside, and the pressure reducing device having the vacuum pump and the pressure reducing control means is provided in the hole. By connecting the decompression suction port and decompressing the inside of the core and the cavity through the hole portion by the decompression device and casting, the following effects are achieved. (1) Improving the fluidity of the molten metal without disturbing the flow of the molten metal, preventing non-rotation and defects in the molten metal. (2) The air and gas generated from the mold are effectively removed without being entrained in the molten metal, and the molten metal is blown and does not generate a wrinkle defect. Therefore, castings such as stainless cast steel or heat-resistant cast steel having a complicated shape and thin wall can be produced soundly.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a vacuum casting apparatus showing an embodiment of the present invention.

FIG. 2 is an external view of a turbine housing.

FIG. 3 is a vertical sectional view of a turbine housing.

FIG. 4 is an external view of a core.

FIG. 5 is a partial vertical cross-sectional view showing another embodiment of the present invention in which vacuum suction is performed from the core cavity.

FIG. 6 is a partial vertical cross-sectional view showing a comparative example of the embodiment.

FIG. 7 is a partial plan view showing casting defects of a cast product in a comparative example.

[Explanation of symbols]

1: breathable mold, 2: cavity, 3: molten metal, 4: ladle, 5: spout, 6: runner, 7: weir, 8: core, 9: core cavity, 10: void 10a: the opening of the hole, 1
1: feeder, 12: decompression device, 13: decompression suction port, 14:
Vacuum pump, 15: Decompression degree control means, 16: Pipe, 1
7: core skirting part, 19: turbine housing, 26: suction member, 27: mold cavity part, 28: blown, wrinkle.

Claims (4)

[Claims] 1. A reduced pressure casting method for casting molten metal by depressurizing an air permeable mold having a cavity, a core, a sprue and a weir, wherein a core is embedded in a cavity forming portion in the air permeable mold, A hole portion communicating with the outside is provided in the core skirting portion of the core, and a vacuum pump and a pressure reducing suction port of a pressure reducing device having a pressure reducing degree control means are connected to the hole portion, and the void is provided by the pressure reducing device. A reduced pressure casting method, characterized in that casting is performed while reducing the pressure inside the core and the cavity through a hole. 2. The reduced pressure casting method according to claim 1,
A reduced pressure casting method, wherein a core hollow portion communicating with the hole provided in the core skirting portion is provided in the core. 3. The reduced pressure casting method according to claim 1, wherein the reduced pressure value of the hole is larger than the reduced pressure value of the sprue. 4. The reduced pressure casting method according to claim 1, wherein gas suction from the gas permeable mold is shut off to reduce the pressure reduction effect of the core and the cavity through the hole. In order to improve, the reduced pressure casting method is characterized in that a gas suction preventing coating layer is formed on the outer surface of the core skirting portion in which the holes are formed.