JPH03230862A - Pressurized casting method - Google Patents

Abstract

PURPOSE:To miniaturize a pressurizing device by supplying pressurized gas into inner part of a core after losing consumable member supporting a molding sand-made core with molten metal filled up in cavity and executing pressurized casting. CONSTITUTION:The core 2 molded with the molding sand is supported with the consumable supporting member 7 lost with the molten metal in a molding sand-made or metallic mold-made master mold 1. After losing the consumable supporting member 7 by filling lip the molten metal into the cavity 4 constituted with this core 2 and the master mold 1, the pressurized gas is supplied from pressurizing source 10 in the inner part in the core 2 to pressurize the metal in the cavity 4 from the surface of core 2 through particle gaps in the molding sand constituting the core 2. By this method, the structure is made to fine over the whole casting and the mechanical property is improved, and also the miniaturization and the operationability of pressurizing device can be improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a pressure casting method.

(Prior art) By pressurizing molten metal (hereinafter referred to as molten metal as necessary) injected into the cavity of a mold, the structure of the resulting casting is densified (preventing the occurrence of casting bundles).
Pressure casting methods for improving mechanical properties are generally known.

In other words, what causes internal defects called cavities in castings is
This is mainly because the density of the metal increases as the temperature decreases during solidification of the metal. In other words, the cavity occurs when the metal contracts within the cavity and the shrinkage cannot be compensated for by the solidified metal. The pressurization of the metal plays an effective role in preventing the formation of such cavities.

By the way, in this pressure casting, as typified by die casting, a large pressure (1,000 to 2,000 atmospheres) is usually applied to the molten metal, so the mold is designed to withstand this large pressure. is applied.

In contrast, in recent years, with advances in casting technology, it has become possible to obtain sound castings without voids even when pressurizing molten metal at relatively low pressures (about several hundred atmospheres). Instead, there is an attempt to use pressure casting in a sand mold.

For example, JP-A-63-137564 discloses that after filling the cavity of a mold made using foundry sand by the lost form method with molten metal, the entire mold is pressurized in a high-pressure gas container. A proposal has been disclosed to apply pressure to the molten metal in the mold.

(Problems to be solved by the invention) In the case of die casting using the above-mentioned mold, there is pressure loss because the metal is pressurized from the sprue side away from the product cavity, and the cavity has a complicated shape. In this case, the metal injected into the complex-shaped part has a large heat dissipation area and solidifies quickly, making it difficult to effectively apply pressure to the details of the cavity. Therefore, this die casting requires a very high pressing force as mentioned above, so the pressing means becomes large and the high pressure causes the problem of core breakage. Casting shaped products is also difficult.

On the other hand, in the case of the above proposal using a sand mold, a large pressurized container is required, and the lid of the pressurized container must be opened and closed, making it difficult to control the timing of pouring into the cavity and applying pressure, which reduces production efficiency. It becomes difficult to increase. In addition, in the case of this proposal, the pressurized gas would reduce the adhesion between the molten metal and the mold, so the solidification rate of the molten metal would not increase, and therefore the metal structure would be difficult to become dense and the mechanical properties would not improve. I can't hope for much. Moreover, since the pressurized container is pressurized after pouring the metal into the cavity, the timing of pressurization after pouring is delayed, and if the cavity has a complex shape, the pressure will not be poured into the complex-shaped part. Because the metal in the cavity solidifies early, it is difficult to apply pressure evenly to the details of the cavity.

That is, an object of the present invention is to easily pressurize molten metal and prevent leakage of pressurizing gas in a pressure casting method using a sand mold without using a large pressurized container. .

(Means for Solving the Problems) The present invention solves these problems by supporting a core made of foundry sand with a fugitive member that disappears with the heat of molten metal, and filling the cavity with molten metal. By causing the fugitive support member to disappear and then supplying pressurized gas to the inside of the core, the metal in the cavity can be pressurized from the surface of the core.

In other words, the specific method is to support a main mold by a fugitive supporting member that disappears with the heat of the molten metal, and to place the molten metal into a cavity formed by the core and the main mold. After that, pressurized gas is supplied to the inside of the core to remove the metal in the cavity from the surface of the core through the gaps between the particles of the foundry sand that constitutes the core. This is a pressure casting method characterized by applying pressure (hereinafter, this will be referred to as the first method).

In this case, the main mold itself may be molded from foundry sand or may be a mold. Moreover, various casting alloys ranging from light alloys to cast iron can be used as casting metals.

Further, the pressurizing pressure can be increased from the discharge pressure to several tens of atmospheres, or even higher as long as the main mold can withstand it.

In addition, various materials can be used for the fugitive support member, as long as they are melted by heat and substantially disappear, such as expanded polystyrene.

In the first means, the core is provided with a protrusion that protrudes upward from the sprue, and when the cavity is filled with molten metal, the protrusion is exposed above the surface of the molten metal. At the same time, a sealed space is formed above the molten metal surface, and then pressurized gas is supplied to the sealed space, thereby supplying pressurized gas from the protrusion to the inside of the core to remove metal from the surface of the core. At the same time as pressurizing, it is possible to pressurize the metal from the molten metal surface (hereinafter, this will be referred to as the second means).

(Operation) In the first means, when molten metal is injected into the cavity, the fugitive support member melts and disappears due to the heat of the molten metal and is replaced by the molten metal, and the core is held by the metal in the cavity. That will happen. In other words, when the molten metal comes into contact with the core, this contact area immediately starts to solidify and forms a solidified or semi-solidified layer around the core, so that the core is held by this layer.

This means that the pressurized gas supplied inside the core applies pressure from the core surface to the metal in the cavity through the gaps between the particles of the foundry sand, which means that the metal is applied from the inside through the core. It means being under pressure. In this case, since the core is prevented from coming into contact with the main mold by the casting metal replaced by the fugitive support member, no pressurized gas leaks to the outside.

In other words, when the core is supported on the main mold by a baseboard, even if the metal comes into contact with the baseboard in a molten state due to its surface tension, it cannot enter into minute recesses on the surface of the baseboard. Therefore, minute gaps are likely to be formed between the baseboard surface and the metal. Although it is easy for the pressurized gas from the core to escape to the main mold side through these micro-gaps,
As mentioned above, since the core is held by the casting metal, there is no problem of leakage of pressurized gas, and there is no need to take any special sealing means to prevent this gas leakage.

In addition, since pressure can be applied to the metal inside the cavity from the inside, the metal inside the cavity is pressed against the main mold, which accelerates cooling and achieves a relatively high solidification rate. This is advantageous in terms of densifying the structure of the casting and improving its mechanical properties.

Furthermore, the ability to apply pressure to the metal inside the cavity from the inside means that even if the cavity has a complex shape, the pressure can be applied to even the smallest details of the cavity.

Therefore, even when a product with a complicated shape is cast, there will be no unevenness in the density of the structure.

In addition, the core itself is equivalent to the pressurized gas that acts on the metal, so it is not directly affected by the pressurizing force, and even if the core has thin parts, the problem of breakage will occur. Never.

Furthermore, since the metal is pressurized through the core, there is no need for a large pressurizing container, making it possible to downsize the pressurizing device and simplifying the pouring and pressurizing work.

In the second method, a part of the core is made to protrude from the surface of the metal and pressurized gas is supplied to the sealed space above it, so that the metal in the cavity can be exposed to the surface of the core. It becomes possible to pressurize at the same time.

In other words, although there is only one pressurizing system, the metal inside the cavity can be pressurized from both the inside (core surface) and the outside (molten metal surface).

(Effects of the Invention) According to the first means, a core made of foundry sand is supported by a vanishing pillar member, the cavity is filled with molten metal to vanish the vanishable supporting member, and then the core is Since the pressurized gas is supplied inside, the metal can be pressurized from the inside without leaking the pressurized gas to the outside with a relatively simple structure, and without causing damage to the core. Even when casting a shaped product, it is possible to apply pressure to the details of the cavity while improving the density of the structure or improving the mechanical properties of the entire casting.Moreover, it is possible to miniaturize the pressure device. , pouring and pressurizing work become easier.

According to the second method, a part of the core is made to protrude from the surface of the metal hot water, and pressurized gas is supplied to the sealed space above the core to separate the metal in the cavity from the surface of the core and from the hot water surface. Since the pressure is applied at the same time, it becomes possible to effectively pressurize the metal inside the cavity from the inside and outside using one system of pressurizing means.

(Example) Embodiments of the present invention will be described below based on the drawings.

0 In this example, a cup-shaped product is cast from an aluminum alloy (AI-8Si, hereinafter simply referred to as aluminum alloy).

In Figure 1, 1 is the main mold, 2 is the core, 3 is the pressure lid, 4
is a product cavity constituted by the main mold 1 and the core 3. The main mold 1 is a metal mold, and the core 3 is made of self-hardening molding sand (the sand is No. 6 silica sand) containing a resin hardening agent, and has air permeability.

A sump 6 is formed in the main mold 1 around a sprue 5. The core 3 has a fugitive support member 7 at the bottom of the cavity of the main mold 1.
It is supported so as not to come into contact with the main mold 1 by a chisel, and has a protrusion 2a that protrudes upward from the sprue 5. The fugitive support member 7 is molded from expanded polystyrene. The sump 6 is for storing molten metal into which the flange of the pressurizing lid 3 is immersed.

That is, as shown in FIG. 2, the pressurizing lid 3 has a flange immersed in the molten metal in the sump 6 to form a sealed space 8 above the sprue 5 to which pressurized air is to be supplied. It is made to protrude into the closed space 8. This pressure lid 3 has a control valve 9 for opening and closing the passage.
A pressurization source 10 is connected through a pressure supply passageway provided with a pressure supply passage. The pressurizing lid 3 and the control valve 9 are integrated into a unit, and this pressurizing unit is mounted on the robot.

Next, each step in pressure casting of the aluminum alloy product will be explained in order.

Assembling the mold The core 2 is supported on the main mold 1 by the fugitive support member 7 so that the protruding part 2a projects upward from the sprue 5 and so that the main mold 1 and the core 2 do not come into contact with each other. do.

Note that a mold coating agent is applied to the main mold 1 and the core 2 to prevent molten metal from being inserted during pressurization.

Pouring - pouring molten metal (aluminum alloy molten metal) from sprue 5 into cavity 4
The molten metal is injected into the molten metal so that the molten metal is collected in the molten metal reservoir 6. In this case, the protruding portion 2a of the core 2 is partially exposed above the surface of the molten metal.

As a result, the fugitive support member 7 is softened and gasified by the heat (approximately 710° C.) of the molten metal, penetrates into the inside of the core 2, disappears, is replaced by the molten metal, and the core is wrapped with this metal. In this state, the main mold 1 is held so as not to come into contact with it.

Closing the pressurizing lid The robot equipped with the pressurizing unit is moved above the sprue 5, and the flange of the pressurizing lid 3 is immersed in the molten metal of the tundish 6, so that a sealed space 8 is created above the sprue 5. Make it. That is, the molten metal portion into which the flange of the pressurizing lid 3 is immersed is rapidly solidified by contact with the flange.
As a result, the space 8 above the sprue 5 is sealed.

- Open the pressurization control valve 9 and supply pressurized gas (compressed air) of 2.5 atmospheres from the pressurization source 10 to the closed space 8. As a result, the pressurizing force of the pressurized gas is transmitted from the surface of the sprue 5 to the metal, and the pressurized gas is supplied to the inside of the core 2 from the core protrusion 2a exposed from the surface of the metal. The pressurizing force caused by the gas acts on the metal from the surface of the core 2, that is, from the inside, through the gaps between particles of the foundry sand of the core 2. This pressurized state is then maintained until the solidification of the metal is completed.

In this case, the metal in the cavity 4 is not only pressurized from the sprue 5, that is, from the outside, but also from the inside via the core 2, and is pressed against the main mold 1. As a result, heat dissipation from this main mold 1 is promoted and the solidification rate increases. Since the metal is pressurized from the inside and a high solidification rate is obtained, the crystal grains of the casting become fine and the structure becomes dense, thereby improving mechanical properties. Further, since the pressing force is applied to the metal from the entire surface of the core 2 that is in contact with the metal, the entire surface of the metal is evenly pressurized.

This means that even if the cavity shape is complex, the pressing force can be applied to the details of the cavity, and there will be no unevenness in the density of the metal structure.

The main mold 1 is disassembled to take out the cast product, the pressurizing lid 3 is removed, and the core sand is taken out.

In the above example, since the main mold is a metal mold, it is possible to apply a pressure higher than 2.5 atm, but when using a sand mold, a pressure as low as about 2.5 atm can be applied at the early stage of solidification of the metal. This allows high pressure to be applied in the latter half of solidification. In this case, the metal in the cavity is subjected to high pressure with a solidified layer formed in the contact area with the sand mold, so this solidified layer partially absorbs the pressing force, causing the load on the main mold 1. becomes smaller. Therefore, even if the main mold is a sand mold, a relatively high pressing force can be applied to the metal without any backup means and without causing damage to the main mold. Of course, the core itself is not affected by the pressure force so much that it will not be damaged.

In addition, when combining multiple cores to obtain a product with a complex shape, if the difference in the solidification time of the molten metal in each part of the cavity becomes large, it is necessary to connect the pressure system from the core side to each core. It is also possible to separate the pressure systems into a plurality of independent pressure systems for each core or for each core, so that the pressure control of each part of the cavity can be performed independently.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a cross-sectional view showing the core supported by the main mold before pouring, and FIG. 2 is a cross-sectional view showing the condition after pouring. 1... Main mold 2... Core 2a... Protrusion 3... Pressure lid 4... Cavity 5...・Gate a...Disappearance support member 10...Pressure source and other 2 people 6

Claims (2)

[Claims] (1) A core molded from foundry sand is supported by a fugitive support member that disappears with the heat of the molten metal in the main mold, and the molten metal is filled into the cavity formed by the core and the main mold, and the above disappears. The method is characterized in that the supporting member is made to disappear, and then a pressurized gas is supplied to the inside of the core to pressurize the metal in the cavity from the surface of the core through the gaps between the particles of the foundry sand constituting the core. Pressure casting method. (2) The core is provided with a protrusion that protrudes upward from the sprue, and when the cavity is filled with molten metal, the protrusion is exposed above the surface of the molten metal;
By forming a sealed space above the molten metal surface and then supplying pressurized gas to this sealed space, the pressurized gas is supplied from the protruding part to the inside of the core, and the metal is pressurized from the core surface. At the same time, the metal is pressurized from the surface of the hot water.
) Pressure casting method described in .