JPH035060A - Mold for reduced pressure suction casting - Google Patents

Abstract

PURPOSE:To manufacture a sound casting by forming coating layer restraining gas venting to surface of a cope, making a core hollow and arranging core gas venting hole communicating to the hollow part in the cope. CONSTITUTION:The cope 2 and drag 4 are formed of molding sand. The core 8 is set in a cavity 6 formed with both molds 2, 4. The prescribed molten metal is sucked under reduced pressure into the cavity 6 in the mold through sucking holes 10 arranged in the drag 4. Then, on at least any one side of the upper face of the cope 2 or the cavity face in the mold, the coating layer 14 for restraining or preventing the gas venting is formed. Together with this, the core 8 is made to hollow and the core gas venting hole 12 communicating to this hollow part 8a is arranged into cope 2. By this method, gas involution into the casting product can be effectively restrained or prevented.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a mold for vacuum suction casting, and in particular to a mold used in a vacuum suction casting method in which a predetermined molten metal is drawn directly into the mold from a melting furnace or the like for casting. This is related to the improvement of.

(Background technology) The vacuum suction casting method, which has been proposed as a casting manufacturing method in recent years, utilizes the air permeability of the mold to reduce pressure, as disclosed in Japanese Patent Application Laid-Open No. 77968/1983. By suction, a predetermined molten metal is sucked into the cavity of the mold and filled to perform casting,
More specifically, a shell mold or a general sand mold consisting of an upper mold and a lower mold is held in a chamber, and a suction hole provided in the lower mold part is immersed in molten metal, while the pressure inside the chamber is reduced. This is a method of producing the desired casting by sucking molten metal through the suction holes in the lower mold, filling the mold cavity with the molten metal. This method produces thin-walled metal, which is difficult to manufacture with the conventional sand casting process. , it has the characteristic that castings with complex shapes can be produced relatively easily.

However, in such a vacuum suction casting method,
It is recognized that if the casting conditions or the mold used are inappropriate, cavity defects with a diameter of about 1 to 10 mm will occur in the resulting casting. Therefore, this defect is
Air entrainment during casting is thought to be the main cause, and when an organic self-hardening mold is used, entrainment of combustion gas from the organic binder is also presumed to be involved.

Therefore, the present inventors conducted various tests on molding and casting conditions to prevent the occurrence of such cavity defects, and found that using a mold with a core placed in the mold cavity, it was possible to achieve the intended purpose. When producing castings, if the gas in the mold cavity is sucked through the core part during vacuum suction casting, the molten metal will flow into the mold cavity along the core surface, effectively entraining the gas into the cast product. They have discovered that this can be suppressed or prevented, and have completed the present invention.

(Problem to be Solved) Under such circumstances, an object of the present invention is to provide a mold for vacuum suction casting that can produce sound castings free of cavity defects.

(Solution Means) In order to solve the above problem, the present invention is composed of an upper mold and a lower mold formed using molding sand, and a core is placed in a mold cavity formed by both molds. In the vacuum suction casting mold, the predetermined molten metal is suctioned under reduced pressure into the mold cavity through a suction hole provided in the lower mold. A coating layer that suppresses or prevents ventilation is formed on at least one of the cores, and the core is hollow, and a core gas vent hole communicating with the hollow part is provided in the upper mold. .

(Specific configuration/example) By the way, the vacuum suction casting mold targeted by the present invention is as follows:
For example, as shown in FIG. 1, it is composed of an upper mold 2 and a lower mold 4 formed using a predetermined molding sand, and these upper mold 2 and lower mold 4 are It is a mold that is molded by a molding method and has air permeability, such as a green mold, a shell mold, or a self-hardening mold. In addition, a core 8 is placed inside the mold cavity 6 formed by these two molds.
A product casting space is formed between this core 8 and the inner surfaces of both molds. Furthermore, it communicates with the product casting space,
Generally, a plurality of molten metal suction holes 10 are provided in the lower mold 4,
As shown in the figure, an opening is formed on the lower surface of the lower mold 4.

The present invention aims to suppress the depressurization from the entire upper mold and strengthen the depressurization from the core part in a mold for vacuum suction casting having such a structure. Thus, the core 8 is a hollow core having a hollow portion 8a. A core gas vent hole 12 communicating with the hollow part 8a of the core 8 is provided in the upper mold 2, so that air is actively exhausted from the core by suction from the upper mold side. There is.

Furthermore, this strengthening of the vacuum from the core part
By forming a coating layer 14 that suppresses or prevents ventilation of the upper mold 2 on at least one of the upper surface of the upper mold 2 and the inner surface of the upper mold forming the mold cavity 6,
It is encouraged.

That is, the presence of the coating layer 14 suppresses or prevents ventilation from the upper surface of the upper mold 2 during vacuum casting, thereby reducing the amount of exhaust from the hollow part of the core 8 through the core gas vent holes 12. It will be increased.

The coating layer 14 can be formed using a mold coating agent that is generally used for mold coating, but it can also be formed using a slurry used in the lost wax method, water glass, etc. In any case, a coating layer 14 that is more airtight than the second mold 2 is formed using a known suitable fire-resistant material, thereby increasing the airtightness of the upper mold 2,
This suppresses the depressurization from the entire upper mold during molten metal suction.

A vacuum suction casting operation using a mold having such a structure is carried out in a known manner. For example, as shown in FIG.
8, move the decompression chamber 16,
The molten metal suction hole 10 of the lower mold 4 constituting the mold 18 is connected to the melting furnace 2.
The molten metal 22 is immersed in a predetermined molten metal 22 housed in a furnace such as No. Suction, casting space in mold 18 (6)
After filling the inside of the tank, casting is performed.

In such vacuum suction casting, in the mold 18 having the above-described structure according to the present invention, the airtightness of the upper mold 2 is increased due to the presence of the coating layer 14, and the airtightness of the upper mold 2 is increased due to the presence of the coating layer 14. Due to the presence of the mold cavity 6, the gas in the mold cavity 6 is effectively exhausted through the core part, so that the sucked molten metal flows into the mold cavity 6 along the surface of the core 8 and fills it. As a result, the entrainment of gas into the resulting cast product is eliminated or prevented, making it possible to produce sound castings free of cavity defects.

Experimental Example A shell mold having the structure shown in Fig. 1 was used, and the core (8) was a hollow shell core, and a core gas vent hole communicating with the hollow part (8a) of the core (8) was used. (12) to 1
While forming on the upper mold (2) with a size of 0 mmφ,
A commercially available coating agent was applied to the top surface of the upper mold to form an airtight coating layer (14), and five exhaust manifold specimens each having a wall thickness of 2.5 mm and a product unit weight of 2.5 kg were placed.
Vacuum suction casting. In addition, as for the molten metal, steel type: SC
313 at a casting temperature of 1575°C.

In addition, for comparison, five of the above specimens were cast under the same conditions using a shell mold in which no coating agent was applied to the upper surface of the upper mold.

The ten exhaust manifold specimens obtained by this casting were each examined for cavity defects using gamma rays, and the results are shown in Table 1 below.

Table 1 As is clear from the results in Table 1, in accordance with the present invention, an airtight coating layer of mold coating agent is formed on the upper surface of the upper mold, and the core is made hollow, and a hollow portion communicating with the hollow portion is formed. When vacuum suction casting was performed using a mold with a secondary gas vent hole (specimen No.

In samples 1 to 5), almost no cavity defects were observed, and only one sample (No. 5) had a cavity defect with a diameter of about 1 mm.

On the other hand, when casting is performed using a mold that does not form a coating layer of mold coating agent on the upper surface of the upper mold,
As seen in specimens Nos. 016 to 10, many cavity defects with large diameters were observed.

(Effects of the Invention) As is clear from the above description, the vacuum casting mold according to the present invention suppresses the vacuum from the entire upper mold and strengthens the vacuum from the core. As a result, the sucked molten metal flows into the mold cavity along the core surface and fills the mold cavity, effectively suppressing or preventing gas entrainment into the cast product, thereby closing the cavity. A sound casting without defects can be advantageously produced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view showing one embodiment of a mold for vacuum suction casting according to the present invention, and FIG. 2 is an explanatory diagram showing a vacuum suction casting method using such a mold. 2: Upper mold 4; Lower mold 6: Mold cavity 8: Core 8a: Hollow part 10: Suction hole 0: Core gas vent hole: Coating layer: Decompression chamber: Melting furnace 18: Mold 22: Molten metal

Claims (1)

[Claims] Consisting of an upper mold and a lower mold formed using foundry sand,
Further, a core is placed in a mold cavity formed by these two molds, and a predetermined molten metal is suctioned under reduced pressure into the mold cavity through a suction hole provided in the lower mold. In the mold, a coating layer that suppresses or prevents ventilation is formed on at least one of the upper surface of the upper mold and the mold cavity surface, and the core is hollow and communicates with the hollow part. A mold for vacuum suction casting, characterized in that a core gas vent hole is provided in the upper mold.