JP2003334634A - Evaporative pattern casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaporative pattern casting method excellent in removal effect for decomposition gas from an evaporative pattern. <P>SOLUTION: The pattern having a through-hole is buried in casing sand to form a mold. A mold is cast in the mold, and the pattern is evaporated to produce an article. The gas produced by evaporation of the pattern is discharged outside of the mold by means of a discharge passage and the gas is burned by feeding an oxidizing gas. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disappearing model casting method, and more particularly, when performing casting while discharging gas generated by disappearing a model to the outside of a mold through a discharge passage,
The present invention relates to a disappearance model casting method for preventing harmful gas generated during casting from being released into the atmosphere by supplying an oxidizing gas.

[0002]

2. Description of the Related Art The vanishing model casting method is also called a full molding method, and is a process of using a model made of synthetic resin foam as a mold while being embedded in molding sand. This process pyrolyzes the synthetic resin foam with the molten metal that is cast.However, a large amount of pyrolysis gas containing soot is generated, and the environment is deteriorated, such as the generation of offensive odors, and the residue causes a cast product. There is a drawback that casting defects occur.

As a technique relating to degassing, Japanese Patent Application Laid-Open No. Hei 5-
Japanese Patent No. 261470 discloses a method of providing a ventilation path communicating with an exhaust port inside a model.
In Japanese Patent Publication No. 77, a method of forcibly discharging the generated gas to the outside through the molding sand while sucking the external gas, and in Japanese Patent Laid-Open No. 11-90583, the generated gas can be smoothly discharged to the outside of the mold. Disappearance model casting is disclosed.

Further, as a technique relating to a gas purification method,
Japanese Unexamined Patent Publication (Kokai) No. 4-344867 discloses a method of forcibly sucking and burning harmful gas generated during casting, unmolding, and the like.

[0005]

By forcibly discharging the generated gas as described above, the casting quality can be improved to some extent, but the molten metal in the mold is disturbed, and the purpose is not always achieved. Not necessarily.

Further, a device such as a vacuum pump is required for forcibly sucking the generated gas, and a pump having a high ability is required for sucking all the gas generated from the entire model.

Therefore, the optimum discharge of the generated gas can be achieved, a casting of excellent quality with few residue defects can be obtained, and the generated gas can be simply and intensively processed (reduction of soot and odor). If possible, the utility value in this industry is considered to be extremely high.

[0008]

According to the present invention, when a molten metal is poured into a mold in which a synthetic resin foam model is embedded in a molding sand, the product is cast while the model disappears by the molten metal. In addition, the gas generated by the disappearance of the model (hereinafter referred to as the generated gas) is discharged to the outside of the mold through a discharge passage, preferably a discharge passage equipped with a discharge gas suppressing means, and the casting is performed. The present invention relates to a model casting method, in which an oxidative gas is supplied to a generated gas and the generated gas is burned, so that the model gas disappears.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The outline of the vanishing model casting method of the present invention will be described with reference to FIG. The mold comprises a casting frame 4, a molding sand 7 inside the casting frame 4, a model 1 embedded in the molding sand 7, and the like, and a receiving port 5 communicating with the model 1 is provided on the upper left side. The model 1 is made of expanded polystyrene in the same shape as the product, and has a through hole 2. Foundry sand 7 is No. 5.5 silica sand, and contains an appropriate amount of a binder. In forming the mold, first, the mold coating agent 3 having excellent fire resistance is applied to the surface of the model 1 and then sufficiently dried. Then, after forming the sprue 6 and the runner 10 in the casting frame 4, the model 1 is fixed and embedded in the foundry sand 7, and the receiving port 5 is installed. that time,
The inside of the through hole 2 is left as a space, and a discharge pipe communicating with the through hole 2 is provided as a discharge passage 8. The exhaust pipe that becomes the exhaust passage 8 is made of ceramic, and is filled with refractory particles 9 such as alumina molded with a binder as exhaust gas suppressing means.
It is embedded in the foundry sand 7 so that the through hole 2 and the atmosphere can communicate with each other.

When the molten metal is poured from the receiving port 5, the molten metal reaches the model 1 through the sprue 6 and the runner 10, melts the model 1, and collects in the mold. On the other hand, it is confirmed that the generated gas from the model 1 melted and burned by the hot water is discharged from the discharge passage 8, but since the refractory particles are filled, the discharge of the generated gas is adjusted. .

As described above, in the present invention, the generated gas generated by the combustion and disappearance of the model is discharged to the outside of the mold through the discharge passage. Preferably, the generated gas is not forcibly discharged almost at the same time as its generation, but is gradually discharged while suppressing the discharge amount by opening the discharge passage provided with the discharge gas suppressing means. By gradually discharging the generated gas to the outside of the mold in this way, the turbulence of the molten metal in the mold can be controlled. In addition, the exhaust gas suppressing means is a means having breathability that allows the generated gas to be gradually released to the outside by providing the means, and is preferably made of refractory particles and their layers, a back pressure valve, and a hollow thin tube. Further, the refractory particles and the layer thereof, and the back pressure valve are preferable from the viewpoint that they also have the functions of preventing the molten metal from blowing out and filtering soot.

As the breathable refractory layer used as the exhaust gas suppressing means of the present invention, a refractory particle is molded by adding a binder or the like, or a ceramic slurry is immersed in urethane foam and then fired. A so-called ceramic foam filter or the like can be used, and the former is preferable. The average particle size of the refractory particles is preferably 0.1 to 10 mm, more preferably 0.5 to 5 mm,
Particles of metal or its oxide, such as alumina, silica sand, zircon sand, chromite sand, synthetic ceramic sand, etc. may be mentioned. The refractory material is preferably filled in an amount such that the thickness is 0.5 to 20 cm, more preferably 1 to 10 cm, depending on the area and shape of the discharge passage. When the hollow thin tube is used as the exhaust gas suppressing means, the inner diameter is 0.1 to 5 cm and the length is 30 cm to 5.
m, further, inner diameter 0.5 cm to 2 cm, length 40 cm to 2
It is preferable that m is composed of a fire resistant material such as metal.

The back pressure valve is a valve whose pressure in the gas flow direction can be set lower on the rear side (downstream of the gas flow path) than on the front side (upstream of the gas flow path) of the valve. Any of a spring type low pressure valve and a needle type may be used, and the exhaust gas suppressing means is formed by installing these in the exhaust passage.

The diameter, the installation position, the number, etc. of the discharge pipes serving as the discharge passages are determined by the shape and size of the model. The discharge passage is preferably formed by a cylindrical, preferably ceramic, exhaust pipe having a diameter of 30 cm or less, preferably 1 to 10 cm. The number of foams may be appropriately determined so as to ensure a desired air permeability, but
It is preferable to provide one per 100,000 cm ³ , preferably 1,000 to 10,000 cm ³ . When the hollow thin tube is used as the suppressing means, the thin tube may be directly installed on the model.

The present inventor uses an oxidizing gas as the generated gas discharged from the discharge passage when the discharge passage, preferably the discharge passage provided with the discharge gas suppressing means, is used in the disappearance model casting method as described above. It was found that soot and offensive odors can be dramatically reduced by supplying and burning the generated gas.

The oxidizing gas is preferably supplied in the discharge passage. Further, it is preferable to supply the oxidizing gas downstream of the exhaust port of the exhaust gas suppressing means of the exhaust passage. Specifically, as shown in FIG. 1, the introduction pipe 12 may be communicated with the discharge passage 8 and the oxidizing gas may be forcibly supplied by a pump or the like (not shown). The oxidative gas may be self-supplied by providing a suction mechanism (FIG. 2) for moving the gas.

The oxidizing gas is not particularly limited as long as it promotes combustion of the generated gas, but air, oxygen gas, or a mixture thereof is preferable.

Normally, since the generated gas is at a high temperature, it naturally burns by supplying the oxidizing gas. However, in order to assist the combustion of the generated gas, a pilot fire 11 is installed as shown in FIG. May be.

As the model, a model made of synthetic resin foam is used. As the synthetic resin foam, a foam such as polystyrene, polymethylmethacrylate, or a copolymer thereof is used.

It is preferable to form a through hole in the model. In particular, it is preferable to form a through hole that communicates with the discharge passage 8 provided with the exhaust gas suppressing means and further communicates with the runner 10. The through-holes may be formed at the time of model production, or after the model production, heated metal rods, drills,
It may be formed by laser, or may be formed by making an incision with a cutter knife or the like and then attaching an adhesive tape or the like to the model surface. Through hole diameter, formation position,
The number etc. is determined by the shape and size of the model.

Incidentally, due to the restriction from the means for forming the through hole,
When the through hole can be formed only at a position close to the runner or the discharge passage, it is preferable to form the through hole as close to these as possible.

A mold coat layer is formed on the model with a mold coat agent. In the present invention, since it is less necessary to discharge gas through the mold-coating film, as the mold-coating agent, besides the commercially available mold-coating agent, a particle size of 10 μm or less, which cannot be usually used in the conventional full-molding method, preferably 1 to It is possible to use a material containing a refractory aggregate having a fine particle diameter of 10 μm.
As a result, the surface smoothness of the coating film is improved, and the surface smoothness of the casting is also improved. Conventionally, when a mold-coating agent containing a refractory aggregate with a fine particle diameter was used in the disappearance model casting method, the permeability of the mold-coating film was lowered, and residual defects and gas defects were observed to increase. The disappearance model casting method of the invention solves such a problem. Further, by forming a thick mold coating layer having a thickness of 2 to 10 mm to form a high-strength mold coating film, it is possible to use refractory particles having a large particle size (1 mm or more) to improve the filling property. Examples of the refractory aggregate in the coating agent include graphite, zircon, magnesia, alumina and silica. In addition, as a binder of a coating agent, in the case of an aqueous system, sodium polyacrylate, starch, methyl cellulose, polyvinyl alcohol, sodium alginate, water-soluble polymers such as gum arabic and emulsions of various resins such as vinyl acetate,
Further, in the case of an alcohol type, it is preferable to add various resins which are soluble or dispersible in alcohol from the viewpoint of coating strength.
The addition amount is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the refractory aggregate.

As the casting sand used for casting, in addition to silica sand containing silica as a main component, new sand or reclaimed sand such as zircon sand, chromite sand, and synthetic ceramic sand is used. Foundry sand can be used without adding a binder, and in that case the filling property is good, but when strength is required, it is recommended to add a binder and cure with a curing agent. preferable.

[0024]

Example 1 A foamed model 1 (made of expanded polystyrene) of 120 mm × 80 mm × 250 mmH was heated with a metal rod having a diameter of 3 mm,
The through hole 2 was formed as shown in FIG. The diameter of the through hole 2 was about 4 mm.

A cylindrical ceramic tube with an inner diameter of 4 cm (length 20 c
m) was filled with spherical alumina 9 having a diameter of 5 mm and containing an ester-curable phenol resin so as to have a thickness (h) of 10 cm, and cured to form a discharge passage 8.

An inlet pipe 12 for feeding air is provided above the alumina-filled layer of the discharge passage 8 as shown in FIG.
At the time of casting, air was fed from here at a ventilation rate of 80 L / min. However, the pilot fire 11 of FIG. 1 was not provided.

A coating agent 3 is applied to the surface of the model 1 in which the through holes are formed.
(80 Baume) was applied and dried, followed by molding according to FIG. Cast iron material is FC-250, casting temperature is 140
It was 0 ° C. The composition of the coating agent was 40% by weight of silica powder (average particle size 8 μm), 10% by weight of scaly graphite, 5% by weight of vinyl acetate binder, 40% by weight of water, and 0.5% by weight of nonionic surfactant. The bentonite was 4.5% by weight.

Table 1 shows the results of evaluation of soot and offensive odor generated from the discharge passage during casting.

Example 2 Casting was performed in the same manner as in Example 1 except that a suction mechanism as shown in FIG. 2 was provided in the discharge passage in place of the introduction pipe for feeding air, and the introduction of air was made self-contained. The same evaluation as in Example 1 was performed. The results are shown in Table 1.

Example 3 Casting was performed in the same manner as in Example 1 except that pure oxygen gas was introduced at 20 L / min instead of air, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 1 Casting was performed in the same manner as in Example 1 except that the casting was performed without sending in air, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[0032]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a vanishing model casting method of the present invention.

FIG. 2 is a schematic view showing an example of a discharge passage provided with a suction mechanism.

[Explanation of symbols]

1 model 2 through holes 3 Coating agent 4 flasks 5 mouth 6 gate 7 Foundry sand 8 exhaust passage 9 Refractory particles 10 runways 11 kinds of fire

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadashi Kusube             2-1-3 Bunka, Sumida-ku, Tokyo Kao Quay             Car Co., Ltd. (72) Inventor Takeshi Nakagawa             2-1-3 Bunka, Sumida-ku, Tokyo Kao Quay             Car Co., Ltd.

Claims (5)

[Claims] 1. When a molten metal is poured into a mold in which a synthetic resin foam model is embedded in foundry sand, and the product is cast while the model is disappeared by the melt, the model disappears. A disappearance model casting method in which a generated gas (hereinafter, referred to as a generated gas) is discharged while being discharged to the outside of the mold through an exhaust passage, and an oxidizing gas is supplied to the generated gas to generate the generated gas. Disappearance model casting method to burn. 2. The vanishing model casting method according to claim 1, wherein the exhaust passage is provided with an exhaust gas suppressing means. 3. The vanishing model casting method according to claim 1, wherein the oxidizing gas is air, oxygen gas or a mixture thereof. 4. The vanishing model casting method according to claim 1, wherein an oxidizing gas is supplied in the discharge passage. 5. The vanishing model casting method according to claim 1, wherein a suction mechanism is provided in the discharge passage to supply an oxidizing gas.