JP3783877B2 - Vacuum casting method - Google Patents

Description

【００１９】
通気性鋳型１内で鋳鋼鋳物が凝固後、搬送装置で次の型ばらしステーション（図示せず）に搬出する。そして、鋳造前の別の通気性鋳型１を注湯ステーションに搬入する。上述の工程を繰り返し、必要とする数の鋳鋼鋳物を鋳造する。
図２および図３に示すフランジ付き複雑形状の薄肉鋳鋼鋳物を８０個鋳造して鋳物の品質を調査した。その結果、溶湯の注入速度が速く、かつ溶湯が乱れにくく、空気や鋳型から発生するガスを溶湯中に巻き込くことなく、全数、不廻り、湯境、吹かれ、湯じわ等の鋳造欠陥の発生は無く、健全であった。
【００２０】
図５は、中子空洞部から減圧吸引を行う他の実施の形態を示す縦断面図である。通気性鋳型（主型）１のキャビティを形成する部位に埋設された中子８の外周と通気性鋳型１との間にキャビティ２が形成される。この鋳造品は複雑形状で、図５に示すように、両側に耳状の薄肉部２を有し、この薄肉部を形成するために埋設した中子８は、この部位が厚く形成されており、当然のことながら中子からの発生ガスは多いと考えられる。従って、中子空洞部を減圧吸引口１３から垂直に上方に延ばし、その先端を耳状部位の近傍まで達するように形成する。この実施の形態により減圧吸引鋳造を行った結果は、吹かれ等の鋳造欠陥は発生せず、健全な鋳造品を得ることができた。
【００２１】
図６は、実施の比較形態を示す縦断面図である。この比較例においては、埋設する中子８は中実に形成されている。減圧吸引は、キャビティ薄肉部２から吸引部材２６を介して鋳型空洞部２７を通して減圧吸引口１３から減圧装置１２（図示せず）により減圧して鋳造した。吸引部材２６を通気性鋳型１よりも通気が良好な材料で形成したにもかかわらず、図７（平面図）に示すような薄肉部２の近傍に吹かれ、湯じわ状の鋳造欠陥が発生した。このことは、中子８が中実のものであるため、中実中子の外面からのみでは、発生ガスを吸引除去することが不十分であったことを示していると考えられる。
【００２２】
【発明の効果】
以上詳細に説明の通り、通気性鋳型内の中子幅木部に外部と連通する空孔部を設け、該空孔部に真空ポンプと減圧度制御手段を有する減圧装置の減圧吸引口を接続させ、減圧装置により空孔部を介して中子およびキャビティ内を減圧して鋳造することにより、以下の効果を奏する。
（１）溶湯の流れを乱すことなく溶湯の流動性を向上し、不廻り、湯境欠陥を防止する。（２）空気や鋳型から発生するガスを溶湯中に巻き込むことなく効果的に除去し、吹かれ、湯じわ欠陥を発生させない。
従って、複雑形状で薄肉のステンレス鋳鋼や耐熱鋳鋼などの鋳物を健全に製造することができる。
【図面の簡単な説明】
【図１】本発明の実施の一形態を示す減圧鋳造装置の縦断面図である。
【図２】タービンハウジングの外観図である。
【図３】タービンハウジングの縦断面図である。
【図４】中子の外観図である。
【図５】中子空洞部から減圧吸引を行う本発明の他の実施の形態を示す部分縦断面図である。
【図６】実施の形態の比較例を示す部分縦断面図である。
【図７】比較例における鋳造品の鋳造欠陥を示す部分平面図である。
【符号の説明】
１：通気性鋳型、２：キャビティ、３：溶湯、４：取鍋、５：湯口、６：湯道、７：堰部、８：中子、９：中子空洞部、１０：空孔部、１０ａ：空孔部の開口部、１１：押湯、１２：減圧装置、１３：減圧吸引口、１４：真空ポンプ、１５：減圧度制御手段、１６：パイプ、１７：中子幅木部、１９：タービンハウジング、２６：吸引部材、２７：鋳型空洞部、２８：吹かれ、湯じわ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vacuum casting method for casting a breathable mold having a cavity, a core, a gate, and a weir part, and in particular, castings such as thin cast stainless steel and heat-resistant cast steel with complicated shapes, The present invention relates to a vacuum casting method for producing sound without any casting defects such as blown or hot water.
[0002]
[Prior art and problems to be solved by the invention]
Thin castings with a thickness of 5 mm or less partially solidify when the molten metal is poured and comes into contact with the mold, and even if it does not solidify, the viscosity increases and fluidity deteriorates. Defects are likely to occur.
In addition, when casting a thin casting having a complicated shape, gas generated from air or a mold is likely to be caught in the molten metal, and blown to the solidified casting, and gas defects such as water wrinkles are likely to occur. . Therefore, it has been difficult to soundly cast a thin casting having a complicated shape and a thickness of 5 mm or less with a material having poor molten fluidity such as stainless cast steel or heat-resistant cast steel.
[0003]
The present applicant has previously disclosed a vacuum casting mold structure having an embedded core (the core may be hollow or solid) as Japanese Patent Application Laid-Open No. 59-229257. In this method, the product part mold space (cavity) is depressurized through the mold and through the decompression 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 the gas from the mold. In some cases, the intended decompression effect cannot be expected.
[0004]
In addition, in Japanese Patent Application Laid-Open No. 6-55255, the present applicant has a sand mold (core burying) having a cavity, a pouring gate and a feeder or a skein, and a pressure reducing device, and is separated from the weir portion of the sand mold. A hot water supply or a skein is provided at a position, and a hole portion communicating with the outside is provided near the hot water supply or skein, and the pressure reducing device has a suction port that contacts the hole portion, and the hole portion The present invention has proposed a method and apparatus for producing a cast steel casting using a sand mold that performs casting while reducing the pressure inside the cavity by reducing the pressure from the suction port that is in contact with the air. In this proposal, the cavity is depressurized through a feeder or a skein, so the generated gas suction from the cavity embedded in the core is indirect suction. In some cases, the decompression effect is slightly small, and the shape of the cavity with the core having such a thin complex shape has been expected to be further improved by a direct suction method from the core portion.
[0005]
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 thin stainless cast steel and heat-resistant cast steel having a complicated shape and partially having a thickness of 5 mm or less. No casting defects, etc., less air entrained in the molten metal from the mold and blown into the solidified casting, sound castings without causing gas defects such as hot water It is providing the vacuum casting method which can manufacture.
[0006]
[Means for Solving the Problems]
As a result of diligent research in view of the above object, the present inventors have provided a hole in the core skirting board part in the air-permeable mold and reduced the pressure in the core and the cavity from the hole part by using a pressure reducing device. In this way, even in castings such as thin stainless steel and heat-resistant cast steel with complex cores, it is possible to prevent non-rotation and hot water boundary defects, and to solidify the casting without entraining air or gas generated from the mold. The present inventors have obtained the knowledge that a sound casting can be obtained without generating gas defects such as blowing and hot water wrinkles.
[0007]
That is, the casting method of the present invention is a reduced-pressure casting method for casting a molten metal by reducing the pressure of a gas-permeable mold having a cavity, a core, a gate, and a weir part, wherein the core is formed at a cavity forming portion in the gas-permeable mold. was buried, Rutotomoni provided cavity communicating outside the core width wood of the core, and cut off the gas suction from the ventilation mold, said core and said through said cavities In order to improve the pressure reduction effect of the cavity, a gas suction prevention coating layer is formed on the outer surface of the core base plate where the hole is formed, and a vacuum pump and a pressure reduction degree control means are provided in the hole. A vacuum suction port of a decompression device is connected, and casting is performed while decompressing the core and the cavity through the hole portion by the decompression device.
[0008]
Then, a core cavity portion communicating with the hole portion provided in the core base plate portion is provided in the core, and the pressure reduction value of the hole portion is made larger than the pressure reduction value of the gate, and casting is performed. In addition, in order to cut off the gas suction from the air-permeable mold and improve the pressure reducing effect of the core and the cavity through the hole portion, the core base plate portion in which the hole portion is formed A gas suction preventing coating layer is formed on the outer surface of the substrate. This gas suction prevention coating layer uses a zircon coating agent having a particle size smaller than that of silica sand No. 6 as the breathable mold material to form a coating layer having a thickness of 0.1 to 0.4 mm, for example, 0.2 mm. To do.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A hole part communicating with the outside is provided in the core baseboard part in the breathable mold, and a vacuum suction port of a decompression device having a vacuum pump and a decompression degree control means is connected to the hole part. By casting the inside of the core and the cavity through the part, the thin casting with a complicated shape partially having a wall thickness of 5 mm or less is prevented from rotating, causing hot water defects, blows, hot water wrinkles, etc. Therefore, the pressure gradient in the cavity and the molten metal injection speed for casting as a healthy casting can be secured, and in particular, the gas generated from the air and the mold can be effectively removed so as not to get caught in the molten metal.
[0010]
Providing the core with a core cavity that communicates with the hole provided in the core baseboard can further enhance the effect of removing the generated gas.
[0011]
When the pressure reduction value of the hole portion is made larger than the pressure reduction value of the pouring gate, 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 on the thin wall portion of the cavity is improved. The pressure reduction value can be adjusted by changing the number of rotations of the vacuum pump by operating the pressure reduction degree control means.
[0012]
Further, in the vacuum suction, when the air-permeable mold is transported and positioned by a transport device (not shown), the vacuum suction is performed by the pressure-reducing device from the hole portion opened toward the outer surface of the air-permeable mold.
[0013]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a second vacuum casting apparatus according to an embodiment of the present invention. The reduced pressure casting apparatus provided for the present invention comprises a breathable mold 1 and a reduced pressure apparatus 12.
The decompression device 12 includes a vacuum pump 14, a pipe 16 having at one end a decompression suction port 13 connected to the opening 10 a of the hole 10 provided in the core baseboard 17, a decompression suction port 13, and a vacuum pump 14. And a decompression degree control means 15 installed between them.
[0014]
As shown in FIGS. 2 and 3, the breathable mold 1 has a thin scroll portion (a portion serving as an exhaust gas passage) 21 having an outer diameter of 120 mm and a thickness of 3.0 mm by the core 8, and an upper portion and a side portion thereof. Further, a thin cavity 2 having a complicated shape having two flange portions 22 having a thickness of 15 mm and two boss portions 23 having a thickness of 20 mm and a height of 25 mm on the outer peripheral portion of the upper flange is formed. The breathable mold 1 is a cold box type and uses silica sand No. 6. The gate 5 is provided near the center of the air-permeable mold 1, and a runner 6 and a weir portion 7 are provided continuously to the gate 5. The core skirting board portion 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. A filter is preferably disposed between the runner 6 and the weir 7 in order to prevent solid impurities mixed in the molten metal 3 from flowing into the cavity 2. In order to prevent the gas generated from the mold from being sucked into the cavity, it is preferable to form a gas suction prevention coating mold on the inner surface of the air-permeable mold 1 forming the cavity by brushing or spraying.
[0015]
As shown in FIG. 1, the hole 10 of the core skirting board portion 17 of the core 8 embedded in the air-permeable mold 1 is directed upward from the opening 10 a provided on the lower surface of the air-permeable mold 1. And communicates with the core cavity 9. The core cavity portion 9 also extends vertically upward, and its tip extends to substantially the same position as the upper end portion of the substantially egg shape in which the lateral width of the core 8 is maximum. For this reason, the generated gas from the core 8 can be efficiently sucked and removed.
[0016]
The decompression device 12 includes a vacuum pump 14, a decompression degree control means 15, and a decompression suction port 13 that performs decompression suction by bringing the flexible tube into close contact with the air hole 10 of the breathable mold 1.
[0017]
Next, an embodiment of the reduced pressure casting method for producing a cast steel casting by the above apparatus will be described. FIG. 2 is an external view of the turbine housing 19 of the automobile turbo rotor made of heat-resistant cast steel. As shown in FIG. 3, the longitudinal cross-sectional view has a complicated shape. In order to form the hollow portion 20 of the cast product, as shown in FIG. 4, the core 8 embedded in the air-permeable mold 1 is It 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 a thin portion 24 of a cast product) is formed around the core 8. Is done. The breathable mold 1 is carried into a pouring station (not shown) by a transport device. Next, the vacuum suction port 13 from the decompression device 12 is brought into close contact with the air hole 10 of the breathable mold 1. And the pressure reduction value in the void | hole part 10 is made into the range of -100 ~ -20mmHg before pouring, and the pressure reduction value of a void | hole part is made larger than the gate. Thereafter, a predetermined amount of molten metal is poured into the cavity 2 from the ladle 4 to perform casting. The molten metal temperature in the ladle 4 was set to the range of 1500-1600 degreeC. Table 1 shows the chemical composition of the cast steel.
[0018]
[Table 1]

[0019]
After the cast steel casting is solidified in the air-permeable mold 1, it is carried out to the next mold release station (not shown) by the transport device. Then, another breathable mold 1 before casting is carried into the pouring station. The above steps are repeated to cast as many cast steel castings as necessary.
80 pieces of complex cast thin-walled steel castings with flanges shown in FIGS. 2 and 3 were cast and the quality of the castings was investigated. As a result, the casting speed of the molten metal is high, and the molten metal is not easily disturbed. Casting of all, non-rotating, hot water boundaries, blown, hot water wrinkles, etc. without entraining the gas generated from the air or mold. There were no defects and it was healthy.
[0020]
FIG. 5 is a longitudinal sectional view showing another embodiment in which vacuum suction is performed from the core cavity. A cavity 2 is formed between the outer periphery of the core 8 embedded in the portion of the air-permeable mold (main mold) 1 forming the cavity and the air-permeable mold 1. This cast product has a complicated shape, and as shown in FIG. 5, it has an ear-shaped thin part 2 on both sides, and the core 8 embedded to form this thin part has a thick part. Of course, the gas generated from the core is considered to be large. Accordingly, the core cavity is formed so as to extend vertically upward from the vacuum suction port 13 so that the tip thereof reaches the vicinity of the ear-shaped part. As a result of performing vacuum suction casting according to this embodiment, casting defects such as blowing were not generated, and a sound cast product could be obtained.
[0021]
FIG. 6 is a longitudinal sectional view showing a comparative embodiment. In this comparative example, the core 8 to be embedded is formed solid. The vacuum suction was performed by reducing the pressure from the vacuum thin wall portion 2 through the mold cavity 27 through the suction member 26 and from the vacuum suction port 13 using the vacuum device 12 (not shown). Even though the suction member 26 is made of a material having better ventilation than the breathable mold 1, it 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 was insufficient to suck and remove the generated gas only from the outer surface of the solid core.
[0022]
【The invention's effect】
As described above in detail, a hole communicating with the outside is provided in the core skirting board in the breathable mold, and a vacuum suction port of a decompression device having a vacuum pump and a pressure reduction degree control means is connected to the hole. Then, the following effects can be achieved by casting the core and the cavity with a decompression device through the hole.
(1) The fluidity of the molten metal is improved without disturbing the flow of the molten metal, and it is possible to prevent malfunctions and boundary defects. (2) The gas generated from the air and the mold is effectively removed without being involved in the molten metal, and blown and does not cause a wrinkle defect.
Therefore, it is possible to produce a casting having a complex shape and a thin wall such as a stainless cast steel and a heat-resistant cast steel.
[Brief description of the drawings]
FIG. 1 is a longitudinal 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 longitudinal sectional view of a turbine housing.
FIG. 4 is an external view of a core.
FIG. 5 is a partial longitudinal sectional view showing another embodiment of the present invention in which vacuum suction is performed from a core cavity.
FIG. 6 is a partial longitudinal sectional view showing a comparative example of the embodiment.
FIG. 7 is a partial plan view showing a casting defect 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: hole 10a: Opening of hole part, 11: feeder, 12: decompression device, 13: decompression suction port, 14: vacuum pump, 15: decompression degree control means, 16: pipe, 17: core baseboard part, 19: turbine housing, 26: suction member, 27: mold cavity, 28: blown, hot water

Claims (3)

A vacuum casting method for casting a molten metal by depressurizing a gas-permeable mold having a cavity, a core, a gate, and a weir part, wherein the core is embedded in a cavity forming portion in the gas-permeable mold, Rutotomoni provided cavity communicating outside the child width wood, to interrupt the gas suction from the ventilation mold, to improve the effect of reducing the pressure of said core and said cavity through said cavities, A gas suction prevention coating layer is formed on the outer surface of the core skirting portion where the hole is formed, and a vacuum suction port of a decompression device having a vacuum pump and a pressure reduction degree control unit is connected to the hole And performing casting while reducing the pressure inside the core and the cavity through the hole by the pressure reducing device. 2. The reduced pressure casting method according to claim 1, wherein a core cavity portion communicating with the hole portion provided in the core skirting portion is provided in the core. The reduced pressure casting method according to claim 1 or 2, wherein casting is performed with a reduced pressure value of the hole portion larger than a reduced pressure value of the gate.

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