JPH02274364A - Vacuum casting method - Google Patents

Abstract

PURPOSE:To prevent the development of casting defect by reducing pressure in cavity after closing tip part of a sprue tube in a mold with solidification of molten metal, submerging the sprue tube into the molten metal and allowing the molten casting material to flow into the cavity. CONSTITUTION:The pressure in the cavity 7 in the mold 1 is reduced, and the molten metal is poured into the cavity 7 reducing the pressure to execute vacuum casting. Then, the tip part 11a of the sprue tube 11 connected with the sprue 9 in the mold 1 is closed with the solidification of the same molten metal S as the casting material. After that, the pressure in the cavity 7 is reduced to the prescribed pressure. Then, the tip part 11a of the solidified sprue tube 11 is submerged into the molten metal S for casting material in a melting furnace 23 and the solidified metal is remelted and the molten metal S is allowed to flow into the cavity 7 with negative pressure in the cavity 7. By this method, contamination caused by mingling with foreign matter can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vacuum casting method in which the pressure inside the mold is reduced to prevent casting defects.

[Prior Art] In a method of producing castings by press-fitting molten metal into a mold, when pouring the molten metal into the cavity of the mold, the gas remaining in the chitovitty etc. Although some gas is released from the gas vent, a significant amount of gas remains. This gas gets caught up in the casting and forms a nest.
Adversely affects castings.

Therefore, a vacuum casting method exists as a method of reducing the pressure inside the mold cavity to overcome the above-mentioned drawbacks. As an example of this vacuum casting method, for example, JP-A-63-14
9061 publication is known. This publication discloses an example applied to force casting of a magnesium alloy, in which the lower part of the stalk (lower part of the sprue), which is immersed in the molten metal, is closed off by an on-off valve when the pressure inside the chamber is reduced. In the vacuum VI manufacturing method, it is important to improve the airtightness of the sprue.

[Problem to be Solved by the Invention 1] Incidentally, the sprue portion of the mold, which requires airtightness, needs to be opened when molten metal flows into it.

Therefore, conventionally, a thin metal plate with a low melting point that is melted by the molten metal is used for the sealing part of the sprue. For example, aluminum foil is used for aluminum alloys.

However, when such a seal structure is used, the seal portion is deformed into a concave shape when the pressure inside the cavity is reduced, and gas from this portion is placed in a position that causes casting defects in the casting u4. There have been proposals to improve the shape of the seal to prevent deformation of the seal, but each requires the preparation of a separate member in advance, which poses an operational cost problem.

The present invention has focused on the above-mentioned problems, and aims to provide a vacuum casting method that can reduce the pressure inside a cavity to a desired level without using a new sealing member or the like.

[Means for Solving the Problem 1] A vacuum casting method according to the present invention in accordance with this object is a vacuum casting method in which the pressure inside a mold cavity is reduced and molten metal is poured into the reduced cavity. After the tip of the sprue pipe connected to the sprue is closed by solidification of molten metal of the same material as the casting material, the inside of the said capitice is reduced to a predetermined pressure, and then the solidified tip of the sprue pipe is closed. The casting material is immersed in molten casting material to be remelted, and the molten casting material is caused to flow into the cavity by negative pressure within the cavity.

[Function] In such a vacuum casting method, first, the tip of the sprue pipe connected to the sprue of the mold is immersed in a molten metal of the same material as the casting material, and as the molten metal solidifies, the sprue pipe is connected to the sprue of the mold. The tip of the tube is occluded. Next, the pressure inside the mold cavity is reduced. In this case, since the sprue pipe is completely closed by the solidification of the molten metal, air and the like are prevented from entering the cavity, and the pressure inside the cavity can be reduced to the desired pressure.

Thereafter, the tip of the sprue tube is immersed in the molten casting material, and the portion that had blocked the tip of the sprue tube due to solidification is remelted by heat received from the molten casting material. Therefore, the molten casting material into which the sprue is immersed naturally flows into the cavity of the mold, which is under negative pressure.

In this way, in the present invention, since the sprue pipe is closed by solidification of the molten metal, there is no need to close the sprue with a sealing member as in the past, and the sealing performance is improved.
Casting work becomes easier.

[Example] The following is a preferred example of the vacuum casting method according to the present invention.
This will be explained with reference to the drawings.

1 and 2 show one embodiment of the invention. First, before explaining the vacuum ft manufacturing method of the present invention, an apparatus for carrying out the present invention will be explained. In the figure,
1 shows a mold that provides ventilation. This mold 1 may have air permeability in itself, such as a sand mold, or may be a mold with ventilation means provided at the parting part.The mold 1 has a cavity 7 formed therein through which the molten metal flows. , the cavity 7 communicates with a sprue pipe 11, which will be described later, via a sprue 9.

The mold 1 is housed in an airtight chamber 13. The airtight chamber 13 is composed of a surface plate 15 and an upper chamber 17. The surface plate 15 is located below the mold 1, and the upper chamber 17 is placed on the surface plate 15. Both joint surfaces are sealed to ensure sufficient airtightness. A suction port 19 is provided on one side of the upper chamber 17, and this suction port 19 is connected to a pressure reducing means such as a vacuum pump.

A sprue pipe 11 projecting outward is attached to a surface plate 15 of the airtight chamber 13. The sprue pipe 11 is connected to the sprue 9 of the mold 1. This allows the cavity 7 to communicate with the atmosphere via the sprue pipe 11.

As shown in FIG. 2, the tip end 11a of the sprue pipe 11 bulges out to the outer diameter in the radial direction, so that the molten metal adheres to the tip and the sealing performance is improved.

The container 21 shown in FIG.
It has a volume necessary for immersing only 1a, and molten metal of the same material as the casting material is temporarily stored.

This container 21 is constructed of a metal container so that the molten metal can solidify easily.

The melting furnace z3 shown in FIG. 1 melts the casting material, and the tip 11a of the sprue pipe 11 is immersed in the molten metal S of the melting furnace 23.

The airtight chamber 13 that houses the mold 1 is movable vertically and horizontally by means of a conveying means (not shown). Further, a part of the molten metal in the melting furnace 23 is automatically supplied to the container 21 by a molten metal conveying means (not shown). The sequence of movements of these conveying means is not shown! 11 go! A: Controlled by the stomach.

Next, a vacuum casting method using the above apparatus will be explained.

FIG. 1(a) shows the state before casting starts. In this state, the pressure reducing means is stopped, and the pressure inside the cavity 7 is the same as that of the atmosphere.

Next, the melting furnace 23 is
A part of the molten metal S is pumped up, and the pumped molten metal S is transported to a predetermined location and poured into the container 21. When the molten metal S is poured into the container 21, the airtight chiton van 13 containing the mold 1 is transported to a position where the container 21 is placed by mold transport means (not shown). and,
The tip end 11a of the sprue pipe 11 is immersed in the molten metal S in the container 21 by lowering the pouring and conveying means. This state is shown at I in FIG.

The molten metal St, t poured into the container 21 solidifies over time, and the tip 11a of the sprue pipe 11 is filled with this molten metal 5f.
fi is closed by the solidified casting 25. Since the inner wall surface of the container 21 is tapered so that the diameter increases upward, the casting 25 fixed to the sprue pipe 11 can be easily removed from the container 21 as shown in FIG. I can do it. In this case, since the tip 11a of the sprue pipe 11 bulges outward in the radial direction, the casting 25 does not come off from the sprue pipe 11, and the contact area between the casting 25 and the sprue pipe 11 is increased, resulting in a seal. performance is improved. In addition, since the molten metal contracts when it solidifies, the adhesion between the casting 25 and the sprue pipe 11 increases, making it possible to create a nearly perfect sealing function.

When the sprue pipe 11 is blocked by the casting 25 fixed to the sprue pipe 11, the airtight chamber 13 is evacuated by a pressure reducing means (not shown), as shown in n in FIG. be done.

Since the mold 1 housed in the airtight chamber 13 has air permeability, the pressure in the cavity 7 of the mold 1 is also reduced, and the pressure reduction ends when the pressure in the cage 7 is reduced to a predetermined pressure. be done. In this case, since the sprue pipe 11 is closed by the casting 25, the reduced pressure state in the cavity 7 is maintained as it is. In addition, the degree of pressure reduction in this case is desirably less than T or r due to pinhole defects caused by residual air in casting 1]4.

Next, the airtight chamber 13 is transported to just above the melting furnace 23 by a mold transport means (not shown).

When the airtight chamber 13 is positioned at a predetermined position, the airtight chamber 13 is lowered by the mold conveying means, and the airtight chamber 13 is
The tip 11a of the tube 11 is immersed in the molten IS 23. As a result, the casting 25 that closes the tip 11a of the sprue pipe 11 is remelted by the heat received from the molten metal S, and the tip 11a of the sprue pipe 11 is remelted. Therefore,
The molten metal S in the melting furnace 23 is sucked upward by the negative pressure in the caster of the mold 1, and as shown at the mouth in FIG.
) into the cavity 7.

Here, when the molten mS flows into the cavity 7, a considerable amount of gas flows into the cavity 7,
Since the pressure inside the airtight chamber 13 is reduced, the gas that has flowed into the cavity 7 flows out through the air-permeable mold 1.

Therefore, the gas ejected into the cavity 7 is not drawn into the casting, and the generation of cavities is prevented.

[Effects of the Invention] As explained above, when using the vacuum casting method according to the present invention, the tip of the sprue pipe connected to the sprue of the mold is blocked by solidification of molten metal of the same material as the casting material. After that, the inside of the mold cavity is reduced to a predetermined pressure, and then the tip of the solidified sprue pipe is immersed in the molten casting material to be remelted, and the molten casting material is poured into the negative space inside the cavity. Since it is made to flow into the cabin by pressure, the inside of the cabin can be reduced to a desired pressure without using a new sealing member.

therefore,! There is no need to install the seal member before the 5th construction, which simplifies the work. Further, since the N-port pipe is almost completely sealed, the gas ejected into the cavity will not mix into the casting, and casting defects can be prevented. In general, since the material that closes the sprue pipe and the casting material are the same material, contamination of the molten metal due to the mixing of foreign materials is also prevented.

[Brief explanation of drawings]

FIG.
Figure 2 is a partially enlarged cross-sectional view of Figure 1C. 1...Mold 7...Cavity 9...Dark mouth 11...N-mouth pipe 13... ..... Airtight chamber 21 ..... Container 23 ..... Melting furnace 25 ..... Casting S for closing the N-port pipe.・・・
・・・・・・Fuyang

Claims (1)

[Claims] 1. In a vacuum casting method in which the pressure inside a mold cavity is reduced and molten metal is poured into the reduced pressure cavity, the tip of the sprue pipe connected to the sprue of the mold is made of the same material as the casting material. After the cavity is closed by solidification of the molten metal, the pressure inside the cavity is reduced to a predetermined pressure, and then the solidified tip of the sprue pipe is immersed in the molten casting material to remelt it,
A vacuum casting method characterized in that the molten casting material is caused to flow into the cavity by negative pressure within the cavity.