JPH08206777A - Lost foam pattern casting method - Google Patents

Abstract

PURPOSE: To provide a lost foam pattern casting method free from carbon defects in a product. CONSTITUTION: A runner 6 and a suction tube 8 whose one end is open to the atmosphere are connected to a pattern embedded in the casting sand 7, and a vent hole 2 is formed continuous to this suction tube. A discharge tube 10 is provided in a flask 4, and the flask is evacuated by a suction equipment fitted to the discharge tube. When the molten metal is poured from a sprue 5, the combustion gas is discharged from the discharge tube. The outer air is sucked from the suction tube and introduced in the flask, the combustion gas is not retained between the molten metal and the pattern, and the combustion gas contents such as carbon are not melted in the molten metal to cast a product of less defects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vanishing model casting method, and more particularly to a vanishing model casting method in which gas generated from the vanishing model is efficiently discharged to the outside of the mold and there are few defects.

[0002]

2. Description of the Related Art The vanishing model casting method is a casting process in which a model made of a combustible material such as expanded polystyrene is buried in foundry sand, and a molten metal is poured into the product while the model disappears due to the heat of the hot water. The method has the advantage that it can be cast into a precise shape. However, when the model disappears due to the molten metal, various gases and carbon are generated from the expanded polystyrene due to thermal decomposition,
The carbon may remain inside the casting or on the surface of the casting to cause carbon defects in the product, which may adversely affect the quality.

Therefore, conventionally, a suction port is provided in the casting frame to suck the gas inside the mold, and the gas (including carbon particles; the same applies hereinafter) generated from the vanishing model is sucked and discharged to the outside through the casting sand. As described in JP-A-5-261470, an exhaust hole communicating with a model embedded in the sand mold is provided in the sand mold, and gas generated by the disappearance of the model is discharged to the outside of the sand mold through the exhaust hole. We tried to prevent carbon defects in the product.

[0004]

By the way, since the above method is not enough to eliminate carbon defects in the product, the gas is sucked from the outside of the mold and the gas generated in the mold is sucked and discharged to the outside. In this case, the present inventors have noted that the pressure difference between the inside of the mold and the suction pressure has an important meaning. That is, the gas generated by the combustion of the vanishing model can be sucked and discharged to the outside while the pressure difference between the mold and the suction pressure is generated, but the pressure in the mold is equal to the pressure on the suction side. In other words, when the amount of generated gas decreases and becomes almost equal to the suction amount, and only the newly generated gas is sucked to the outside, it burns in the space formed between the hot water and the model. Even if the gas and the like remained, the gas was not sucked to the outside, and the carbon particles in this space remained until the end of the pouring, resulting in carbon defects in the product.

Further, as in the invention described in JP-A-5-261470, even if an exhaust hole is provided in a sand mold, the internal gas cannot be forcibly discharged, and the generated gas is naturally discharged. It was not possible to sufficiently discharge the gas only by discharging it from the outlet until carbon defects were prevented.

[0006]

In order to solve the above problems and to provide a vanishing model casting method that does not cause carbon defects, the present invention uses the following casting method.

In the vanishing model casting method, in which the vanishing model is buried in the molding sand, and the product is cast while the vanishing model is vanished by the poured pouring water, the suction which communicates with the vanishing model. A part, and the space between the vanishing model formed by pouring the hot water and the hot water is conducted to the outside of the mold by the suction part, and the gas in the mold is passed from the outside of the mold through the molding sand. The extinction model casting method is configured such that an external gas is introduced into the space portion through the suction portion and the gas containing carbon particles in the space portion is discharged to the outside of the mold together with the external gas by suctioning did.

In addition to the suction part communicating with the vanishing model, the exhausting part is further communicated with the vanishing model, and after pouring, the gas in the space is sucked from the exhausting part to be introduced through the sucking part. The gas in the space is discharged from the mold together with the external gas from the exhaust unit.

The gas introduced into the space is oxygen or a gas containing oxygen.

The gas introduced into the space is a gas containing no oxygen, such as nitrogen or argon gas.

The gas introduced into the space is pressurized from outside the mold so that the gas is pumped into the space.

[0012]

[Function] When the molten metal is poured into the mold from the gate, the heat of the molten metal melts the model. Since the model melts not only the part directly contacting the hot water but also the upper part thereof, a space is formed between the hot water and the solid part of the model. In addition, the model melted by heat becomes a low molecular weight and becomes a gas state, and is decomposed to generate carbon particles,
Stay in the formed space.

On the other hand, when the inside of the mold is sucked from the outside of the mold, the gas in the space between the hot water and the model is drawn out, and the inside becomes negative pressure, so that the outside gas is introduced from the suction part that is connected to the space. . The gas generated from the model is discharged to the outside of the mold along with the gas introduced from the outside through the suction portion in this way, and the space portion is filled with the outside gas. Therefore, since carbon particles do not remain in this space, carbon defects do not occur in the manufactured product.

Further, when the gas in the space portion is sucked from the exhaust portion provided in addition to the suction portion, the external gas introduced from the suction portion can be sucked directly without passing through the foundry sand. Can be exchanged efficiently.

When a gas containing oxygen is introduced into the disappearance model, the gas generated from the model is completely burned to suppress the generation of carbon particles, and carbon defects are not generated in the product.

When a gas containing no oxygen is introduced into the disappearance model, styrene does not burn and carbonize, so that carbon particles are not generated and carbon defects are not generated in the product.

By pressurizing the gas on the introduction side, the gas can be pumped to the space portion, and the gas in the space portion can be discharged more efficiently.

[0018]

EXAMPLE An example of the disappearing model casting method of the present invention will be described.

FIG. 1 shows an example of a mold for carrying out the vanishing model casting method according to the present invention.

The mold is composed of the flask 4 and the molding sand 7 inside the flask 4.
And a model 1 and the like buried in the foundry sand 7, and a sprue 5 communicating with the model 1 is provided on the upper left side.

The model 1 is formed of expanded polystyrene in the same shape as the product, and has a ventilation hole 2 penetrating vertically.

A discharge pipe 10 is provided below the casting frame 4, and is connected to a suction device (not shown) through the discharge pipe 10. Foundry sand 7 is 5.5 silica sand, and contains an appropriate amount of a curing agent.

To form the mold, first, a mold coating agent 3 having excellent fire resistance and air permeability is applied to the surface of the model 1 and then sufficiently dried. Then, after forming the sprue 5 and the runner 6 in the casting frame 4, the model 1 is fixed and embedded in the molding sand 7. that time,
The inside of the ventilation hole 2 is left as a space, and the suction pipe 8 is attached to the ventilation hole 2.
To provide. The suction pipe 8 is made of ceramic and is embedded in the foundry sand 7 so as to communicate with the vent hole 2 and the atmosphere. Further, the upper surface of the molding sand 7 is covered with a resin film 9 while leaving the gate 5 and the suction pipe 8 to eliminate the air permeability of the upper surface of the molding sand 7.

Next, casting will be described. First, the suction device is operated to suck gas from the discharge pipe 10 provided below the casting mold 4 to reduce the pressure inside the casting mold 4 and then pour molten metal from the sprue 5. The poured water melts the model 1,
Collect in the mold. On the other hand, it can be confirmed that the gas of the model 1 melted and burned by the hot water is discharged from the discharge pipe 10, and that the air is sucked into the mold from the suction pipe 8. It was After that, the suction of air from the suction pipe 8 was continued until the pouring was completed, and when the pouring was completed and the product was inspected, a high quality casting without carbon defects could be obtained.

This is presumed as follows. That is, when the hot water reaches the model 1 through the runner 6, the model 1 is melted and the space above the portion in contact with the hot water is melted by heat, and a space is left between the hot water and the remaining solid model 1. Is formed. The gas (including low-molecularized gas and carbon particles) generated from the disappeared model 1 collects in this space, and when the inside of the casting flask 4 is made negative pressure by suction from the discharge pipe 10, the atmosphere becomes The air introduced into the space through the suction pipe 8 is exhausted to the outside through the exhaust pipe 10 together with the gas from the model 1. As a result, since all the gas and carbon particles from the model 1 are sucked to the outside and do not remain in this space portion, it is presumed that a product of good quality without carbon defects could be obtained.

FIG. 2 shows another embodiment. In this example, an exhaust hole 11 is newly formed in the model 1, an exhaust pipe 12 is provided in communication with the exhaust hole 11 like the suction pipe 8, and a suction device (not shown) is connected to the exhaust pipe 12. It is a thing.

With this structure, the gas from the suction pipe 8 introduced into the space is exhausted to the outside through the exhaust hole 11 and the exhaust pipe 12, and the combustion gas and the like in the space can be discharged more efficiently and quickly. It was possible to form a good product.

Further, when the exhaust pipe 12 is used, the hot water retaining member 1 in which the exhaust pipe 12 is filled with iron balls 15 as shown in FIG.
3 may be provided. The hot water stopper 13 has a wire mesh 14 on the upper and lower sides, and several iron balls 15 having a diameter of about 10 mm are stacked between these wire meshes 14.

When the hot water stopper member 13 is connected to the exhaust pipe 12 in this manner, the gas in the mold can be easily sucked from the exhaust pipe 12 through the gap between the iron balls 15, and the molten metal is stopped by the hot water stopper member 13. Even if the water is filled, it is not pushed up above it, and the molten metal can be prevented from flowing out from the exhaust pipe 12.

The hot water stopper 13 is not made of the iron ball 15 but a stone if the air permeability and heat resistance can be secured.
Other materials such as sand may be used, and the diameter and shape thereof are not limited. Further, it is preferable that the exhaust pipe 12 is provided as far as possible from the suction pipe 8 in order to completely exhaust the internal gas.

Further, if the gas introduced into the suction pipe 8 is air or a gas having a high oxygen concentration, combustion of the model 1 will be good, carbon particles will not remain, and carbon defects will not occur in the product.

On the other hand, if the gas introduced into the suction pipe 8 is an oxygen-free gas such as nitrogen or argon gas, the model 1
Does not burn and only melts, so carbon particles are not generated and carbon defects are not generated in the product.

Further, the pressure of the gas introduced into the suction pipe 8 may be increased by a compression device or the like. This way,
The gas is forcibly blown into the space, and the gas in the space can be scavenged more completely.

[0034]

According to the vanishing model casting method of the present invention, since the suction part communicating with the space between the vanishing model and the hot water is provided, the air inside the mold is sucked to pour the molten metal. The outside air directly flows into the space formed between the disappearance model and the hot water through the suction part and is discharged to the outside of the mold, so that the gas and soot generated from the disappearance model can be completely discharged to the outside,
Does not cause carbon defects in the product.

Since the exhaust part communicating with the space is provided in addition to the suction part and the gas in the mold is sucked and discharged from this exhaust part, the combustion gas in the space is sucked more efficiently,
Can be discharged and does not generate carbon defects in the product.

By using a gas having a high oxygen concentration as the gas to be introduced into the space, the burnup of the model can be increased and the quality of the product can be improved without leaving carbon.

By using a gas containing no oxygen as the gas to be introduced into the space portion, it is possible to improve the quality of the product without leaving carbon.

[Brief description of drawings]

FIG. 1 is a sectional view showing a mold for carrying out an embodiment of a casting method according to the present invention.

FIG. 2 is a sectional view showing a mold for carrying out another embodiment of the casting method according to the present invention.

FIG. 3 is a view showing a hot water stopper member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Model 2 Vent hole 3 Coating agent 4 Casting frame 5 Gate 6 Runner 7 Foundry sand 8 Suction pipe 9 Resin film 10 Discharge pipe 11 Exhaust hole 12 Exhaust pipe 13 Water stop member 14 Wire mesh 15 Iron ball

Claims (5)

[Claims] 1. A vanishing model casting method for casting a product by pouring molten metal into a mold in which a vanishing model is embedded in foundry sand, and casting the product while the vanishing model is vanished by the poured hot water. A suction unit is provided, and the space between the vanishing model and the hot water formed by pouring the hot water is conducted to the outside of the mold by the suction unit, and the casting sand is passed from the outside of the mold into the mold. The extinction model casting method, characterized in that the external gas is introduced into the space portion through the suction part by sucking the gas of (1), and the gas in the space portion is discharged to the outside of the mold together with the external gas. 2. In addition to a suction section communicating with the disappearance model, an exhaust section is further communicated with the disappearance model, and after pouring, the gas in the space is sucked from the exhaust section to be introduced through the suction section. The vanishing model casting method according to claim 1, wherein the gas in the space is discharged from the mold together with the external gas to the outside of the mold. 3. The gas introduced into the space is oxygen or a gas containing oxygen.
Alternatively, the vanishing model casting method according to item 2. 4. The vanishing model casting method according to claim 1, wherein the gas introduced into the space is a gas containing no oxygen. 5. The pressure of the gas introduced into the space portion is set higher than the pressure outside the mold, and the gas is pressure-fed to the space portion. Disappearance model casting method according to item.