JPS60184447A - Casting method using expendable prototype - Google Patents

Abstract

PURPOSE:To obtain a casting having a beautiful casting surface free from defects by using a polymethyl methacrylate foam consisting of a copolymer composed specific weight % of methyl methacrylate and alpha-methyl styrene as an expendable prototype. CONSTITUTION:A polymethyl methacrylate foam consisting of a copolymer of 70-95% methyl methacrylate and 30-5% alpha-methyl styrene is disposed as an expendable prototype 2 in the casting mold 5 of a molding flask 1. A molten metal 9 arrives at the prototype 2 through a runner 3 and the prototype 2 is melted and evaporated by the radiation heat of the molten metal 9 and is thereby substd. with the molten metal 9. The gas generated in the cavity is increased in the pressure by which the gas is passed through the molding sand layer 5 and is diffused and sucked into a jacket 6. Since the foam has a high gasifying rate and decreases the generation of carbide during casting, the casting having a beautiful casting surface without defects is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cast product free of internal casting defects and with a beautiful casting surface. The casting method of the present invention is particularly useful for casting cast steel and cast iron.

A mold is made using a fugitive prototype made of expanded polystyrene,
With this master mold, runners, etc. still filled in the mold, high-temperature molten metal is poured from the sprue, and the foamed polystyrene master mold is sequentially vaporized by the heat of the molten metal, and then replaced with the molten metal to produce a casting. The casting method is known (Special Publications No. 4m-15683, No. 42-8921, No. 43-
No. 13601, No. 44-7921). In this case, in order to prevent casting defects due to gases and residues generated when the original mold disappears due to pouring, it is common practice to drain these gases out of the mold by reducing the pressure.
No. 26, Utility Model Publication No. 48-37613, JP-A-49-13
No. 1912, Special Publication No. 47-38286).

The foamed resin master molds used in these filling casting methods and filling/vacuum casting methods are obtained by molding polystyrene foam beads or by cutting and joining foamed molded products. In particular, if the prototype has a complex shape, or if it is a shape that makes it impossible to pull out the foam product from the mold, it may be created by cutting the foam molding or joining other foam parts. (Special Publications No. 44-7921, No. 45-8201) Often b0 In the filling casting method that uses polystyrene foam as a prototype, when hot iron water is used, the polystyrene that is the prototype material gasifies, but the When the temperature of the hot water is 800° C. or higher, the amount of carbonized residue increases rapidly, and the carbonized residue remains on the surface of the casting, resulting in a disadvantage that the surface of the resulting cast product is rough.

The present invention improves this drawback by using a polymethyl methacrylate resin foam as a molding material to produce products with beautiful casting surfaces, whether cast in high-temperature castings such as iron hot water or low-temperature casting hot water such as aluminum hot water or zinc hot water. method of manufacturing,
That is, a method for manufacturing a casting using a fugitive mold made of a resin foam that vaporizes and disappears when high-temperature molten metal is injected, characterized in that a polymethyl methacrylate resin foam is used as the fugitive mold. A casting method is provided.

The polymethyl methacrylate foam used in the present invention has a high gasification rate compared to polystyrene foam, the presence of oxygen in the molecule, and the fact that the monomer is easily decomposed by heat, so that it generates less carbide during casting. It is believed that it is possible to produce cast products with no defects and beautiful casting surfaces.

In the present invention, polymethyl methacrylate as the fugitive original material is a homopolymer of methyl methacrylate or a copolymer of 70% by weight or more of methyl methacrylate and another vinyl monomer.

As other vinyl monomers, α-methylstyrene is preferred since it improves the polymerizability of methyl methacrylate;
In order to adjust physical properties such as bending strength of the original mold, 20% by weight or less of styrene may be used as a part of α-methylstyrene. Further, in order to improve the impact resistance of the original mold, butyl acrylate, acrylonitrile, 2-hydroxyethyl acrylate, etc. can be used in a proportion of 5% by weight or less.

Specifically, a vinyl monomer mainly composed of methyl methacrylate is subjected to suspension polymerization at a temperature of 95 to 130°C in the presence of a polymerization initiator such as t-butyl peroxybenzoate or benzoyl peroxide to form a resin. After producing particles, and then supplying a blowing agent such as butane, dichlorodifluoromethane, dichlorodifluoroethane, pentane, etc. into an aqueous medium in which the resin particles are dispersed, and impregnating the resin particles with the blowing agent,
Expandable polymethyl methacrylate resin particles were obtained by separating the resin particles from the aqueous medium (Japanese Patent Application Laid-Open No. 1983-36
No. 288, No. 5'l-182333, No. 57-182
(Refer to Japanese Patent No. 334), a prototype is manufactured by filling the expandable particles into a steam molding mold, heating the expandable particles with steam, foaming the particles, and fusing them together.

An example of a device for vacuum casting using this fugitive prototype is shown in the first example.
As shown in the figure. Reference numeral 1 designates a casting flask having a ventilation structure, 2 a fugitive master mold, 3 a runner, 4 a first opening, and 5 a mold made of fluid dry foundry sand containing no binder. A jacket 6 is in contact with the flask 1 having a ventilation structure, and is depressurized by a vacuum pump, ejector, fan, etc. through an exhaust pipe 7.

5-8#'i A lid placed to airtightly cover the upper surface of the mold 5, 9 is a molten metal. While reducing the pressure with this device, the sprue 4
When a more metallic molten metal 9 is injected, the molten metal 9 reaches the master mold 2 through the runner 3, and the master mold 2 is melted and volatilized by the radiant heat of the molten metal 9, replacing the molten metal 9.

When the mold 2 is melted and vaporized by the injected molten metal 9, the pressure inside the resulting cavity increases rapidly, and the generated gas passes through the mold sand layer 5 under reduced pressure and is diffused and sucked into the jacket 6. As a result, the sand particles are strongly consolidated and prevented from collapsing.

In the practice of the present invention, the surface of the polymethyl methacrylate resin foam prototype 2 is coated with a coating material such as graphite, zircon, silica sand, etc. or a resin coating material containing metal powder in order to obtain a more beautiful casting surface. You can leave it there.

Examples of the molten metal include iron, aluminum, bronze, and zinc.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

6 - Manufacturing example of polymethyl methacrylate copolymer prototype Example 1 Methyl methacrylate 657? , α-methylstyrene 180? After dissolving t-butyl peroxybenzoate i, sr in a mixed solution of a vinyl compound consisting of , styrene 361 and n-butyl acrylate 271, the solution was placed in a 3-ton autoclave containing 100ml of water.
The autoclave was charged under stirring at 0 Orpm, and the atmosphere inside the autoclave was replaced with nitrogen gas.

Next, the temperature was raised to 105°C, and after heating and stirring at the same temperature for 5 hours, a 10% aqueous solution of polyvinylpyrrolidone 302 was added, and after further heating at the same temperature for 15 hours, the temperature was raised to 125°C, and butane 602, Toluene 279 was added, and the mixture was further heated and stirred at the same temperature for 5 hours, and then cooled to produce copolymer particles.

After cooling, the copolymer particles were taken out, washed, and air-dried. The average particle diameter of the obtained particles was 0-91rrs, and the total amount of volatile components was 7.05%.

The copolymer particles were pre-foamed with steam at 100°C to obtain pre-foamed particles with an apparent density of 21.6 t/l. The pre-expanded particles were filled into a steam mold having a mold cavity of 50 mm length, 600 mm width, and 50 mm height, heated for 20 seconds using steam at 115°C, and then cooled for 2 minutes to form the mold cavity. Foam product (prototype) with a bulk density of 22.8V/t faithful to
Get a friend.

Examples 2 to 6 Foam products having the bulk densities shown in Table 1 were obtained by suspension polymerization and steam molding in the same manner as in Example 1, except that the composition shown in Table 1 was used as the vinyl monomer.

Examples 1 to 5, Comparative Examples 1 to 2 The foam products shown in Table 1 (fugitive prototypes) were embedded in No. 4 dry silica sand in the mold flask shown in Figure 1, and then heated to 760 cm while reducing the pressure to 400 ■Hg. ℃ molten aluminum or 1,3
Cast iron hot water at 50° C. was poured into the mold to eliminate the original shape, and a cast product having the cast surface and internal structure shown in the table was obtained.

The gasification rate of the prototype was investigated using the following method.

The amount of gas generated in a foam having a density of about 33 y/l in a high temperature atmosphere was measured using a Joke-Fisher gas pressure measuring device. As shown in FIG. 2, it was confirmed that the foam according to the present invention exhibited a faster gasification rate than the commonly used polystyrene foam at a temperature of 700°C.

(Margin below) −〇　− 110-

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of the casting apparatus, and FIG. 2 is a diagram showing the gasification rate of the foam. In the figure, 1 is a casting flask, 2 is a fugitive prototype, 5 is a mold, and 9 is a molten metal. Patent applicant: Yuka no Hitoshi Datessie Co., Ltd. Agent: Patent attorney Hidetoshi Furukawa Agent: Patent attorney Masahisa Hase 11- 1st

Claims (1)

[Scope of Claims] 1) A method for producing a casting using a fugitive mold made of a resin foam that vaporizes and disappears when high-temperature molten metal is injected, wherein the resin foam is a polymethyl methacrylate foam. Characteristic casting method. 2) Polymethyl methacrylate is methyl methacrylate
2.) The casting method according to claim 1, wherein the casting method is a copolymer of 70 to 95% by weight of α-methylstyrene and 30 to 5% by weight of α-methylstyrene.