JPH08155584A - Method for molding casting mold - Google Patents

Abstract

PURPOSE: To decrease casting defects by forming a pattern by using a material which generates carbon dioxide by sublimation or decomposition, embedding this pattern into casting sand coated with water glass, generating the carbon dioxide by sublimation or decomposition, thereby forming a cured layer in the casting sand and dissipating the pattern. CONSTITUTION: The casting sand 3 coated with the water glass is formed by kneading casting mold and water glass and drying the mixture. The pattern 1 is formed by using the material which generates carbon dioxide by sublimation or decomposition, for example, dry ice. The pattern 1 is embedded into the casting sand 3 coated with the water glass and is sublimated. The carbon dioxide is generated and the water glass of the casting sand 3 in contact with the pattern 1 cures by reacting with the gas, by which the cured layer is formed. The pattern 1 sublimates and a cavity is formed. The trouble that cracking gas remains in a casting as with a lost foam pattern method does not arise. Since the cured layer is formed on the cavity surface, the mold collapse at the time of pouring is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a mold used in, for example, a full molding method.

[0002]

2. Description of the Related Art As one of full molding methods, an extinction model method using an extinction model is known. In this vanishing model method, a model is made using a vanishing material such as expanded polystyrene, the model is embedded in casting sand, the molten metal is poured into the buried model, and the model disappears due to the heat. This is a method of casting a casting having the same shape as the model by substituting the poured metal. According to this disappearance model method, there are advantages that the casting equipment is simple and the post-processability such as sand removal is extremely easy.

However, in the vanishing model method, the decomposed gas of the vanishing model may be mixed into the metal to cause a product defect. Further, during casting, the mold may collapse or break before the molten metal is completely replaced with the model, which may cause defects in the cast product. This is because the strength of the sand around the model is weak. In view of this, Japanese Patent Laid-Open No. 61-219443 uses a casting sand containing an appropriate amount of water, and pours a molten metal in a state where the casting sand is frozen after burying the vanishing model to replace the vanishing model with the molten metal. A method of doing so is disclosed. According to this method, since the molding sand around the model has high strength due to freezing, it is possible to prevent the mold from collapsing or breaking.

On the other hand, a so-called carbon dioxide gas molding method is known in which kneading sand to which water glass is added is filled around a model and carbon dioxide gas is blown into it to cure the water glass to form a mold. However, in this method, carbon dioxide gas is blown into the product cavity surface from the side that contacts the back surface, so a large amount of carbon dioxide gas is required to cure the product cavity surface side to the required strength, and it There was a problem that it took time.

In view of this, in Japanese Patent Laid-Open No. 57-50243, a casting frame is placed on a model plate provided with carbon dioxide gas jetting means in the model part, and carbon dioxide gas is jetted from the inside of the product cavity to produce the product cavity surface. A method of curing the side first is disclosed.

[0006]

However, even with the method disclosed in Japanese Patent Laid-Open No. 61-219443, the decomposition gas of the disappearance model is eliminated as long as the disappearance model is disappeared and replaced with the molten metal. The problem of mixing in the metal is not solved, and defects may occur in the cast product. Further, in the method disclosed in Japanese Patent Laid-Open No. 57-50243, no problem occurs if the model is removed after the carbon dioxide gas is jetted to harden the casting sand, but the model may not be removed depending on the shape. If casting is performed with the vanishing model left, similar to the above, problems due to decomposed gas occur.

The present invention has been made in view of the above circumstances, and an object of the present invention is to easily form a casting mold which has high strength of casting sand and which can be poured in a state where a model is removed.

[0008]

[Means for Solving the Problems] The mold forming method of the present invention for solving the above-mentioned problems comprises a first step of forming a water glass-coated casting sand obtained by coating casting glass with water glass, and carbon dioxide gas by sublimation or decomposition. The second to make a model from the material that generates
A step of embedding the model in water glass coated casting sand and generating carbon dioxide gas by sublimation or decomposition to form a hardened layer on the water glass coated casting sand that is in contact with at least the model and the model disappears; Is characterized in that

[0009]

In the first step of the molding method of the present invention, the casting sand is coated with water glass to form a water glass-coated casting sand. This can be easily done by kneading water glass and casting sand of a predetermined concentration and drying. On the other hand, in the second step, a model is made from a material that generates carbon dioxide by sublimation or decomposition.

In the third step, the model is embedded in water glass-covered sand, and if it is dry ice, it is left at room temperature, and if it is carbonate, it is heated.
The model sublimes or decomposes to generate carbon dioxide gas. By this carbon dioxide gas, at least the water glass of the water glass coated sand that contacts the model reacts and hardens, and a hardened layer is formed. On the other hand, the model disappears due to sublimation or decomposition.

As a result, a cavity whose shape is modeled is formed in the portion where the model was present, and a hardened layer is formed on the surface of the cavity, in which the water glass of the water glass coated casting sand has reacted and hardened. . The hardened layer is mainly formed on the cavity surface, and the outer peripheral portion is in a so-called shell type state in which the strength is not high. Therefore, it is possible to easily remove the mold without any extra force at the time of mold release. Moreover, since the hardened layer on the cavity surface is decomposed and collapsed by the heat of the metal after pouring, the time required for a step such as shot blasting performed as a post-treatment is shortened.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. (First step) Water glass and silica sand were kneaded to form water glass-coated casting sand. When silica sand is used as the casting sand, water glass covers 6% by weight of the entire casting sand.

Although silica sand is used in this embodiment, zircon sand, chromite sand, olivine sand, chamotte sand or the like may be used depending on the type and weight of the cast metal. Further, the coating amount of water glass is set according to the type of sand used. (Second step) On the other hand, dry ice powder was filled in a predetermined mold, crushed, and then the mold was opened to manufacture a dry ice model 1 having a cross-sectional shape shown in FIG. Dry ice is most preferable as the material that generates carbon dioxide by sublimation or decomposition, but carbonates such as calcium carbonate and sodium bicarbonate can also be used. Also, the manufacturing method of the model is
For example, a method of filling powders of these materials in a mold and hardening it,
Known methods such as forging and cutting can be used.

The order of the first step and the second step is not limited, and either of them may be performed first, or both of them may be performed simultaneously. (Third step) Next, the casting frame 2 shown in FIG. 2 was prepared and filled with the water glass-coated casting sand 3 formed in the first step. A plurality of through holes 20 are provided at the bottom of the casting frame 2, and the through holes 20
An argon gas supply port 21 is communicated with.

Then, as shown in FIG. 2, the dry ice model 1 was embedded in the water glass-coated casting sand 3 filled in the flask 2. At this time, the dry ice model 1 was embedded while the argon gas was jetted from the supply port 21 through the through hole 20 into the flask 2 to bubble the water glass coated casting sand 3. As a result, the burying of the dry ice model 1 was facilitated, and the portion along the surface of the dry ice model 1 was filled with the water glass-coated casting sand 3 without any gap.

In this state, the dry ice model 1 was left standing at room temperature to release carbon dioxide gas by sublimation, so that the dry ice model 1 disappeared. The carbon dioxide gas is discharged from the surface of the water glass-coated casting sand 3 in contact with the dry ice model 1 through the particles of the water glass-coated casting sand 3 to the outside. And the particles of the water glass coated sand 3 harden while sticking to each other. Since this reaction first occurs on the surface portion of the dry ice model 1, as shown in FIG. 3, carbon dioxide gas and water glass are formed on the surface of the water glass-coated casting sand 3 which constitutes the cavity in contact with the dry ice model 1. The cured layer 4 was formed by the reaction of.

The hardened layer 4 is in a state in which the casting sand is continuously bonded with the hardened water glass, and the gap between the casting sands has a smooth surface filled with the hardened water glass. There is. It is desirable that carbon dioxide is generated at a ratio of 1 to 3 mol with respect to 1 mol of water glass. When the amount of carbon dioxide is less than 1 mol, the strength of the hardened layer is not sufficient, and when it is more than 3 mol, the surface layer hardening reaction is too fast and it is difficult to harden the inside.

(Casting Step) A molten metal 6 of an iron-based alloy or an aluminum-based alloy was poured into the obtained mold 5 as shown in FIG. 4, and after solidification, the mold was released and the cast product was taken out.
In the obtained cast product, the presence of the hardened layer 4 prevented deformation of the mold during pouring, so that the cast product was cast in almost the same shape as the model 1 and the casting surface was good.

Further, since the hardened layer 4 of the mold 5 is mainly formed on the surface of the cavity and is in a shell state, the water glass-covered casting sand 3 occupying most of the mold 5 is in an uncured state, and the mold release is extremely difficult. It could be done easily. Most of the hardened layer 4 is decomposed and collapsed by the heat of the molten metal after pouring. Therefore, the shot blasting process for removing the hardened layer 4 adhering to the cast product can be completed in a short time, and the process can be shortened.

When the model is made of a material such as CaCO ₃ , carbon dioxide gas is generated by decomposition, but CaO is also generated. This CaO has an advantage that it can be used as a desulfurizing agent and the like, but on the other hand, it has a problem that a large amount of slag is generated. Therefore, when using a model formed of such a material, it is necessary to consider the slag catch method.

When dry ice is used, the dry ice has a property of naturally joining when they are in contact with each other. Therefore, an assembly core method for producing a plurality of models and compounding them It is also possible to use the above method.

[0022]

[Effects of the Invention] That is, according to the mold forming method of the present invention, there is no problem that decomposed gas generated remains in the cast product as compared with the conventional disappearance model method. In addition, since the hardened layer is formed on the surface of the cavity, it is possible to prevent the mold from collapsing during pouring. Therefore, defective casting can be reduced.

Further, since the shape collapse is prevented by the existence of the hardened layer on the surface of the cavity, the shape of the cavity is accurately transferred to the cast product. Therefore, if a mold is formed using a model having a precise shape, a precise cast product having the same shape as that of the model can be formed, and it is possible to form a near net shape which has been difficult with the conventional disappearance model method. Furthermore, even when molding a mold for producing a large casting or a casting having a complicated shape, the carbon dioxide gas released from the model surely contacts the entire surface of the cavity to form a hardened layer,
There is no problem that the cured layer is partially immature.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a model produced in one example of the present invention.

FIG. 2 is an explanatory view showing a method of burying a model in water glass-covered molding sand in one embodiment of the present invention.

FIG. 3 is a sectional view of a mold formed in one embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a state of casting using the mold formed in one example of the present invention.

[Explanation of symbols]

1: Dry ice model 2: Casting frame 3: Water glass coating sand 4: Hardened layer 5: Mold 6: Molten metal

Claims (1)

[Claims] 1. A first step of forming a water glass-coated casting sand by coating water glass on a casting sand, a second step of producing a model from a material that generates carbon dioxide gas by sublimation or decomposition, and the model. A third step of embedding in the water glass-coated casting sand to generate carbon dioxide gas by sublimation or decomposition to form a hardened layer on the water glass-coated casting sand that contacts at least the model and to eliminate the model, A method of molding a mold, comprising: