JPH01273644A - Method for casting and lost foam pattern - Google Patents

Abstract

PURPOSE:To cast a high quality casting without any gas defect and rough casting surface by embedding a lost foam pattern composing of foaming grains enclosing inert gas into molding sand to form a mold and pouring molten metal to this lost foam pattern. CONSTITUTION:In pre-foaming process of styrene resin, etc., an accumulating chamber for granular resin is made to reduced-pressure and after heating, the inert gas of nitrogen gas, etc., is introduced to return back to the atmospheric pressure. The lost foam pattern 3 is formed with the foaming grains enclosing inert gas, obtd. with this. The lost foam pattern 3 obtd. with this is set in a flask 1. Successively, the molding sand 9 containing no binder is packed around the lost foam pattern 3, to form the mold. After that, the air in the flask 1 is sucked through pressure reducing chamber 2 to make reduced-pressure state. Successively, the molten metal 10 is poured into the pattern body 4 through a runner 6 and a runner gate 5. The lost foam pattern 3 is decomposed into monomer without burning with heat of the molten metal 10 and extruded into the circumferential sand grains. By this method, the casting having beautiful casting surface without developing gas and unburnt material and without any gas defect of blow hole, etc., is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a casting method using a vanishing model and a vanishing model.

(Prior art) Conventionally, a casting method using a vanishing model, such as a full mold casting method, involves forming a vanishing model as a prototype from a foamed resin, such as expanded polystyrene, and embedding this vanishing model in casting sand. A mold is formed and molten metal is poured into the embedded model. When the foamed polystyrene comes into contact with the molten metal, it immediately burns, and in its place, the mold is filled with the molten metal to perform casting. Note that such a casting method is described, for example, in Japanese Patent Application Laid-Open No. 62-234639.
No. 62-159944.

In this casting method, the model is made of foamed resin, and air is encapsulated in the expandable particles in forming the disappearing model.

(Problem to be solved by the invention) For this reason, when pouring molten metal into a disappearing model made of foamed resin,
Because this part of the foamed resin model is rich in oxygen, the foamed resin that came into contact with the molten metal thermally decomposes and the flammable gas generated burns and is drawn into the molten metal, causing gas defects such as blowholes. There is often a problem that a part of the foamed resin is incompletely combusted and becomes carbonaceous unburnt material that adheres to the surface of the casting, causing roughness in the casting.
It became.

The present invention provides a casting method that can obtain beautiful castings without roughness due to gas defects such as blowholes or adhesion of carbonaceous unburned substances, and is further suitable for casting methods that use disappearing models. The purpose is to provide a model of disappearance.

(Means for Solving the Problems) The casting method of the present invention for achieving the above-mentioned problems involves embedding a vanishing model in which an inert gas is enclosed in expandable particles in casting sand to form a mold. The gist is to pour molten metal into the vanishing model.

(Function) When molten metal is poured into a vanishing model in which inert gas is enclosed in expandable particles, the vanishing model is thermally decomposed into seven parts, but since the interior of the vanishing model is filled with inert gas. In the part replaced by the molten metal, oxygen is diluted and combustion is suppressed, and the monomer remains in liquid form and is pushed out by the pressure of the molten metal from the disappearing model part to between the sand grains of the mold. As a result, flammable gases do not get caught up in the molten metal, gas defects do not occur, and carbonaceous unburned substances due to poor combustion do not occur, making it possible to obtain beautiful castings. can.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4. A decompression chamber 2 formed in the lower part of the flask 1 is connected to an external suction pump (not shown), and is configured to reduce the pressure inside the flask 1 . The vanishing model 3 is made of foamed resin, for example foamed polystyrene, and includes a model body 4, a runner weir 5,
It consists of 6 hot water channels.

As shown in FIG.
It is formed by using an inert gas 8, such as nitrogen gas, sealed in it, and for example, in the pre-foaming process of styrene resin, the chamber containing the granular resin is brought into a reduced pressure state and heated, Next, the particles are filled with an inert gas, such as nitrogen gas, and then returned to atmospheric pressure, thereby enclosing nitrogen gas into the expandable particles. In addition, inert gas 8
Nitrogen gas was given as an example, but the point is that any material that does not react with the monomer even at high temperatures and can suppress its combustion is fine, and oxygen-diluted air, argon gas, So-called inert gases such as helium gas can be used.

Then, the vanishing model 3 molded from the foamed beads obtained in this way is placed on the floor sand that has been spread in advance in the casting flask 1, and the casting sand 9 containing no binder is poured into the flask 1, and is then vibrated. Then, casting sand 9 is filled around the vanishing model 3 to form a mold.

Next, a suction pump (not shown) sucks the air in the flask 1 through the decompression chamber 2 to bring it into a depressurized state.

Then, when the molten metal 10 is poured toward the upper end of the runner 6 of the vanishing model 3, the molten metal 10 is poured into the model body 4 through the runner 6 and the runner weir 5.

As a result of this injection, the vanishing model 3 is thermally decomposed into monomers as shown in Figure 3.4, but since the vanishing model 3 has an inert gas enclosed in the expandable particles, the part of the vanishing model 3 is replaced by the molten metal. is in an oxygen-depleted state, combustion of the monomer 11 is suppressed, and the monomer 11 is forced out between surrounding sand grains by the pressure of the molten metal while remaining in a liquid state.

Therefore, combustion is suppressed in the part of the vanishing model, and as a result, less flammable gas is generated and no unburned carbonaceous substances are generated. As a result, compared to the case of using a conventional vanishing model made of expandable particles filled with air, the product of this example has no gas defects such as blowholes caused by the entrainment of flammable gas, and the surface of the casting is A beautiful cast iron with no unburned carbonaceous substances was obtained.

In this example, the inside of the flask 1 was vacuumed to reduce the pressure, but even if the pressure is not reduced,
Since the seven hammers 11 in the cavity are pushed out between the sand grains by the pressure of the molten metal, it is possible to obtain a product without gas defects or roughness in the casting, similar to the above embodiment. Also, casting flask 1
The same effect as in the above embodiment can be obtained even if the flask 1 is kept in a sealed state and the inside of the flask 1 is suctioned by a suction pump, and the inside of the mold is highly depressurized.

(Effects) As detailed above, according to the casting method of the present invention, since a vanishing model in which inert gas is enclosed in expandable particles is used, combustion of the vanishing model is suppressed in the part replaced with molten metal, The monomer can be discharged in liquid form between the sand grains of the mold, and as a result, it is possible to stably produce beautiful cast products without gas defects.

[Brief explanation of the drawing]

Figures 1 to 4 show examples of the present invention, Figure 1 is a sectional view schematically showing the casting method, Figure 2 is a sectional view showing expandable particles, and Figure 3 is during the casting process. FIG. 4 is a sectional view showing the completed state of casting. ■... Casting flask 2... Decompression chamber 3... Vanishing model 4... Model body 5... Yudo weir
6... Runnel 7... Expandable particles 8.
...Inert gas 9...Casting sand 10...Molten metal 11...Nanatsuma-

Claims (1)

[Claims] 1. Casting characterized by forming a mold by burying a vanishing model in which an inert gas is enclosed in expandable particles in casting sand, and pouring molten metal into the vanishing model. Method. 2. Disappearance model made by enclosing inert gas in expandable particles.