JPH09314309A - Vacuum suction casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evacuated suction casting method by which the separating work for gate part, runner, etc., is unnecessary and the good yield for casting is obtd. without casting defect, by gradually releasing the reducing degree of pressure in a mold housing chamber after filling molten metal into a product cavity. SOLUTION: The mold housing chamber 5 in which a permeable mold is housed is carried by a carrying device. The mold housing chamber 5 is made to air-tight with a clamp 19 and a suction head 17 from an evacuating device 16 is made in close contact with the permeable mold 1. Then, a molten metal introducing hole 8 is dipped into the molten metal 4 in a holding furnace 3, and a prescribed quantity of the molten metal 4 is poured into the product cavity 14 by evacuating the mold housing chamber 5 with the evacuating device 16. After filling up the molten metal, the pressure value in the mold housing chamber 5 is controlled. For example, the arrival vacuum degree is controlled to -400mmHg, and the pressure in this chamber 5 is controlled by a pressure controller 16c so that the pressure value therein is gradually released at 20mm/sec after 30sec from the start of pouring. Then, the molten metal at the upper part of the runner 11 is allowed to gradually flow out into the holding furnace 3. After 50sec from the start of pouring, all molten steel in the runner 11 is allowed to flow out and is dropped into the holding furnace 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum suction casting method for producing castings, and more particularly, to a casting having a complicated shape having a thick wall portion and a thin wall portion using a breathable mold without casting defects. The present invention relates to a vacuum suction casting method that can be obtained soundly and with good injection yield.

[0002]

2. Description of the Related Art Conventionally, as a vacuum suction casting apparatus of this type, as shown in FIG. 5, a weir portion 12 which is branched into a plurality of parts is provided in a mold storage chamber 5 connected to a pressure reducing apparatus (not shown). The product cavity 14 is formed at the end of the
A mold provided with a mold 1 in which 2 is connected to a runner 11 positioned in the longitudinal direction with the center thereof is often used. The molten metal introduction port 8 is connected to the runner 11 from the bottom portion 6 of the mold storage chamber 5, and the molten metal introduction port 8 is immersed in the molten metal in the holding furnace 3 and the depressurizing device is operated, so that the molten metal 4 Is filled into the product cavity 14 through the molten metal inlet 8, the runner 11 and the weir 12. Then, the molten metal 4 in the mold 1 begins to solidify with the outer shell portion, the product cavity 14, and the dam portion 12. When the weir portion 12 is half solidified and the pressure is released to return to atmospheric pressure, the molten metal 4 of the runner 11 falls into the holding furnace 3 and the inside of the runner 11 becomes substantially hollow. Then, the casting product is obtained by removing the casting mold 1 from the casting mold storage chamber 5 and removing sand to remove the weir portion 12.

[0003] In order to prevent thinning and shrinkage cavities in the above vacuum suction casting, the molten metal in the unsolidified portion of the product cavity is not allowed to flow out when the reduced pressure is released, and the product cavity is supplemented with solidification shrinkage. It is necessary to supply molten metal from the road. For this purpose, it is conceivable to prolong the immersion time of the molten metal inlet in the holding furnace or to lower the pouring temperature. However, if the immersion time is lengthened, it will take time to cast and the productivity will decrease, and the mold storage chamber will be easily damaged by the radiant heat from the molten metal.If the pouring temperature is lowered, casting defects such as whirling and blowout will occur. Is likely to occur.

In order to solve these problems, Japanese Patent Laid-Open No. 1-1437
In Japanese Patent No. 53, the riser is formed above the product cavity of the mold, and the top of the riser and the top of the runner are communicated with each other via the weir portion and vacuum suction is applied to the product cavity and the riser. There is a disclosure in which the molten metal is filled with molten metal by holding the reduced pressure for a short time to prevent the occurrence of shrinkage cavities in the casting in the product cavity by filling the molten metal and then releasing the reduced pressure inside the mold housing chamber.

In Japanese Utility Model Publication No. 3-7066, in a vacuum suction casting method for storing a breathable mold 1 in a mold storage chamber 5 as shown in FIG. By forming the connecting path 15 in 12, the connecting path 15 is completely solidified, and further, the reduced pressure is released in the state of going from the weir portion 12 to the runner 11 to return the molten metal 4 in the runner 11 to the holding furnace 3, There is a disclosure that facilitates coagulation time management and weir folding operations.

[0006]

However, in Japanese Patent Laid-Open No. 1-143753, since the riser is provided on the upper part of the product cavity, the injection yield is deteriorated and the size of the mold is increased, so that the mold cost is increased. Increase.

The Japanese Utility Model Publication No. 3-7066 discloses that
To prevent shrinkage cavities in castings with thick walls, runner 1
Since it requires a large amount of molten metal replenishment from 1, the vacuum suction holding time is long. The weir portion 12 has a time difference in solidification due to an initial temperature gradient due to the flow of molten metal and heat transfer from the molten metal in the holding furnace, and thus it is difficult to prevent lack of wall or shrinkage cavities in the thick portion, and the runner 11 or Since the molten metal in the weir portion 12 cannot be returned to the holding furnace 3, the injection yield becomes poor.

[0008] The object of the present invention is to solve the above-mentioned problems of the prior art, and by using a breathable mold, even in a complex casting having thick and thin parts, such as lack of wall, shrinkage cavity, non-rotating, blown, etc. It is an object of the present invention to obtain a vacuum suction casting method which has no casting defect and can be manufactured with a high injection yield without the need for separating work such as dams and runners.

[0009]

In order to solve the above-mentioned problems, a vacuum suction casting method of the present invention comprises a mold storage chamber having an opening at the bottom, a molten metal introduction port projecting from the opening, and the mold. It is stored in a storage chamber, a runner is connected to the molten metal inlet, a plurality of weirs are branched from this runner, and an air-permeable mold in which a product cavity is formed from the weir and the mold storage chamber are decompressed. A depressurizing suction casting method comprising a depressurizing device, immersing the molten metal inlet into the molten metal in the holding furnace, and introducing the molten metal into the product cavity by controlling the degree of depressurization of the depressurizing device. After the molten metal is filled, the degree of pressure reduction in the mold storage chamber is gradually released.

The depressurization degree in the mold accommodating chamber is released by repeating pressure release and holding at least once. In addition, before the molten metal introduction port is immersed in the molten metal, the inside of the mold accommodating chamber is brought to atmospheric pressure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. (First Embodiment of the Invention) FIG. 1 is a longitudinal sectional view of an essential part showing an example of an apparatus for casting an exhaust manifold by a vacuum suction casting method of the present invention. The casting apparatus includes a mold storage chamber 5 having an opening at the bottom 6, a molten metal inlet 8 provided so as to project from the opening, and a melt passage 11 connected to the molten metal inlet 8 which is stored in the mold storage chamber 5. A plurality of weirs 12 are branched from the passage 11 and an air-permeable mold 1 in which a product cavity 14 of an exhaust manifold is formed from the weirs 12 and a decompression device 6 for decompressing and controlling the mold storage chamber 5. Then, the molten metal introduction port 8 is immersed in the molten metal 4 in the holding furnace 3 and the degree of pressure reduction of the pressure reducing device 16 is controlled to inject the molten metal 4 into the product cavity 14.

Specifically, the breathable mold 1 is a cold box type silica sand No. 6 and the core has an outer diameter of 50 m.
m, 2.0 mm thick thin-walled port, 5 flanges with 15 mm thick on the upper and side parts, and 3 bosses with 15 mm outer diameter and 25 mm height laterally on the thin-walled port. To form the product cavity 14 of the exhaust manifold with a complex shape and thin wall. The runner 11 has a diameter of 75 mm,
It is provided near the center of the breathable mold 1.

The decompression device 16 comprises a vacuum pump 16a, a pressure control device 16c, a control valve 16b, and a pressure sensor 18, and a suction head 17 is brought into close contact with the aeration mold 1 in the mold storage chamber 5 to perform vacuum suction.

The exhaust manifold made of heat resistant cast steel shown in Table 1 is cast by the above casting apparatus.

[0015]

[Table 1]

A mold storage chamber 5 containing the breathable mold 1 is loaded into a pouring station (not shown) by a carrier device. Next, the mold storage chamber 5 is made airtight by the clamp 19, and the suction head 17 from the pressure reducing device 16 is attached to the breathable mold 1.
To adhere. And 1540 to 1560 of the holding furnace 3
The molten metal inlet port 8 is immersed in the molten metal 4 at 0 ° C., the mold storage chamber 5 is decompressed by the decompression device 16, and a predetermined amount of the molten metal 4 is injected into the product cavity 14. After the molten metal is filled, the pressure control device 1 controls the pressure value in the mold storage chamber 5 to change with time as shown in FIG.
Controlled by 6c. The ultimate decompression degree is set to -400 mmHg, and the pressure control device 1 is set to gradually release the pressure value in the mold storage chamber 5 at 20 mmHg / sec from 30 seconds after the start of injection.
6c is controlled. Then, the molten metal in the upper part of the runner 14 is gradually discharged into the holding furnace 3. 50 seconds after the start of injection-
When the pressure reaches 100 mmHg, the mold storage chamber 5 is raised to complete the immersion, and all the molten metal in the runner 11 flows out and falls into the holding furnace 3.

After completion of the immersion, the suction head 17 is separated from the breathable mold 1 and the clamp 19 is released. After that, the transfer device (not shown) is used to move to the next unmolding station (not shown).
To carry out. Then, another mold storage chamber 5 in which another air-permeable mold 1 before casting is stored is carried into the pouring station.
Repeat the above steps to cast the required number of exhaust manifolds.

80 exhaust manifolds were cast and the quality was investigated. As a result, from the runner 11 to the product cavity 14
The molten metal 4 of the runner 11 can be almost returned to the holding furnace 3 even if the molten metal 4 is sufficiently replenished and there is no casting defect such as lack of wall, shrinkage cavities, non-rotation, blown, etc. It was possible to omit the work of separating the weir and the runway, and to manufacture with good injection yield.

(Embodiment 2) FIG. 3 is a longitudinal sectional view of an essential part showing another example of an apparatus for casting a turbine housing by the vacuum suction casting method of the present invention. Casting equipment
A mold storage chamber 5 having an opening in the bottom portion 6, a molten metal introduction port 8 projecting from the opening, and a melt passage 11 connected to the molten metal introduction port 8 which is accommodated in the mold storage chamber 5 and is connected to the weir 11 from the weir. Part 1
2 a plurality of branches, and from the weir portion 12, the upper mold and the lower mold are combined to form one stack of four permeable molds that form a product cavity 14 of the turbine housing, and a decompression device 6 that decompresses and controls the mold storage chamber 5. Consists of. Then, the molten metal introduction port 8 is immersed in the molten metal 4 of the holding furnace 3 and the degree of pressure reduction of the decompression device 16 is controlled to introduce the molten metal 4 to the product cavity 14.

Specifically, the breathable mold 1 is a cold box type silica sand No. 6 and the core has an outer diameter of 120 m.
m, a thickness of 3.0 mm, a thin scroll part, two flange parts with a thickness of 15 mm on the upper and side parts, and two boss parts with a thickness of 20 mm and a height of 25 mm on the outer periphery of the upper flange. The product cavity 14 of the turbine housing having a complicated shape and a thin wall is formed. The runner 11 has a diameter of 80.
mm, and is provided near the center of the breathable mold 1.
1 is provided with a weir 12 and a product cavity 14. A molten metal inlet 8 is provided at the bottom of the mold storage chamber 5 so as to communicate with the runner 11.

The decompression device 16 comprises a vacuum pump 16a, a pressure control device 16c, a control valve 16b, and a pressure sensor 18, and the suction head 17 is closely attached to the aeration mold 1 in the mold storage chamber 5 to perform decompression suction.

A turbine housing made of heat-resistant cast steel having the composition shown in Table 2 is cast by the above casting apparatus.

[0023]

[Table 2]

A mold storage chamber 5 containing the breathable mold 1 is loaded into a pouring station (not shown) by a carrier device. Next, the mold storage chamber 5 is made airtight by the clamp 19, and the suction head 17 from the pressure reducing device 16 is attached to the breathable mold 1.
To adhere. And 1530 to 1550 of the holding furnace 3
The molten metal inlet port 8 is immersed in the molten metal 4 at 0 ° C., the mold storage chamber 5 is decompressed by the decompression device 16, and a predetermined amount of the molten metal 4 is injected into the product cavity 14. After the molten metal is filled, the pressure control device 1 adjusts the pressure value in the mold storage chamber 5 to the time change shown in FIG.
Controlled by 6c. The ultimate decompression degree is -450 mmHg, the pressure value in the mold storage chamber 5 is released at 100 mmHg / sec for 1 second from 30 seconds after the start of the injection, and then the pressure value is held at that pressure value for 9 seconds. The pressure control device 16c is controlled to repeat three times according to the height of the stacked breathable molds 1. Then, the molten metal in the upper part of the runner 14 is gradually discharged into the holding furnace 3. After 60 seconds from the start of injection, when the temperature becomes −150 mmHg, the mold storage chamber 5
Is raised to end the immersion, and all the molten metal in the runner 11 flows out and falls into the holding furnace 3.

After the immersion, the suction head 17 is moved to the breathable mold 1
And the clamp 19 is released. After that, it is carried out to the next demolding station (not shown) by the carrying device. Then, another mold storage chamber 5 in which another air-permeable mold 1 before casting is stored is carried into the pouring station. The above steps are repeated to cast the required number of turbine housings.

120 turbine housings were cast and the quality was investigated. As a result, the molten metal is sufficiently replenished from the runner 11 to the product cavity 14, and without the provision of a riser, there are no casting defects such as wall deficiency, shrinkage cavities, non-rotation, blown, etc. Was almost returned to the holding furnace 3, and the work of separating the weir and the runner could be omitted, and the injection yield could be increased.

[0027]

As described above, the vacuum suction casting method of the present invention has a thick portion and a thin portion by gradually releasing the degree of pressure reduction in the mold storage chamber after filling the product cavity with the molten metal. A casting having a complicated shape can be cast with high injection yield without casting defects such as lack of wall, shrinkage cavities, non-rotation, and blowing, and without the need for separating work such as weirs and runners.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of a casting apparatus used in an embodiment of the present invention.

FIG. 2 is a pressure control diagram in the casting apparatus used in the embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a main part of a casting apparatus used in another embodiment of the present invention.

FIG. 4 is a pressure control diagram in a casting apparatus used in another embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a main part of a conventional casting apparatus.

FIG. 6 is a longitudinal sectional view of a main part of a conventional casting apparatus.

[Explanation of symbols]

1: Breathable mold 2: Depressurized space 3:
Holding furnace, 4: molten metal, 5: mold storage chamber,
6: bottom part, 7: flexible pipe, 8: molten metal inlet, 11: runner, 12: dam part, 14:
Product cavity, 16: Vacuum suction casting device, 16a:
Vacuum pump, 16b: control valve, 16c: pressure control device, 17: suction head, 18: pressure sensor,
19: Clamp.

Claims (3)

[Claims] 1. A mold storage chamber having an opening at the bottom, a molten metal introduction port provided so as to project from the opening, and a mold storage chamber which is stored in the mold storage chamber and is connected to the molten metal introduction port. A plurality of weirs are branched from the weir, and an air-permeable mold in which a product cavity is formed from the weirs, and a decompression device for decompressing and controlling the mold storage chamber. The molten metal inlet is immersed in the molten metal in the holding furnace. A vacuum suction casting method of introducing molten metal into the product cavity by controlling the degree of decompression of the decompression device, wherein after gradually filling the product cavity with molten metal, the degree of decompression of the mold storage chamber is gradually released. And a vacuum suction casting method. 2. The reduced pressure suction casting method according to claim 1, wherein the releasing of the degree of pressure reduction of the mold storage chamber is performed by repeating pressure release and holding at least once. 3. The vacuum suction casting method according to claim 1, wherein the mold storage chamber is set to the atmospheric pressure before the molten metal inlet is immersed in the molten metal.