JPH02205226A - Lost foam pattern - Google Patents

Abstract

PURPOSE:To manufacture a beautiful Mg alloy casting by dispersing sulfur powder into a foaming body constituting a lost foam pattern. CONSTITUTION:The sulfur powder 2 is dispersed into the foaming body composed of the polystyrene foaming particles 1 constituting the lost foam pattern 3. In order to manufacture this lost foam pattern, ethyl alcohol is added to the sulfur powder and stirred to make this slurry-state having suitable viscosity. This slurry-state sulfur is added to polystyrene beads at about 10vol.% and stirred and this mixed polystyrene beads are charged into a foaming machine with the ordinary method and foamed at about 80 deg.C to form the lost foam pattern. By this method, the productivity of the casting can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fugitive model for casting, particularly to a fugitive model used when casting a molten magnesium alloy.

(Prior art) One of the casting methods is the so-called full mold casting method, in which a fugitive model placed in a mold is filled with molding sand containing an organic binder, and molten metal is poured into it. (For example, see Japanese Patent Publication No. 52-11645).

In this method, the heat of the molten metal hardens the organic binder, while the heat of the molten metal causes the fugitive model to disappear. The voids created by this disappearance are filled with molten metal to form a casting. During such casting, gases generated from the filling sand and fugitive pattern are exhausted through the gaps in the filling sand. Further, since the filling sand becomes even hotter, the organic binder deteriorates, and therefore the sand can be easily removed, making it easier to take out the casting.

The material for the disappearing model must be a material that decomposes at the temperature of the molten metal without leaving substantially any residue, and for this reason styrofoam is mainly used. Since the presence of particles in the fugitive model will impede the formation of spheroidal graphite in the casting, foamed styrene heavy duty that does not contain any sulfur is used as the fugitive model for full mold casting of iron alloy castings. The combination is JP-A-62-97.
Although disclosed in No. 743, the presence of sulfur does not have a negative effect on casting unless the casting is made of cast iron containing graphite, and when the chemical reaction between the molten metal and a fugitive model or sand mold must be particularly suppressed, It is known that it is advantageous to include a flame retardant such as powder.

(Problem Z to be solved by the invention) By the way, when casting a magnesium alloy (hereinafter referred to as Mg alloy) using a fugitive model as described above,
Due to the chemical reaction between the Mg alloy and the fugitive model and sand mold,
A deterioration layer is formed on the surface of the cast product. The altered layer occurs because
This is because the Mg alloy reduces 5iOz, which is the main component of sand, and produces metallic silicon.

As a preventive measure, it is necessary to apply a flame retardant such as sulfur powder to the surface of the fugitive model or sand mold, but this application process is difficult to automate and must be done manually, which reduces productivity. Significantly worsen the situation.

The present invention was made for the purpose of solving the above problem, and the problem to be solved is to solve the problem by using a vanishing model.
An object of the present invention is to provide a fugitive model capable of suppressing the formation of a degraded layer on the surface of a product when casting g-alloy castings.

Means for Solving the Problems> To achieve this, the fugitive model of the present invention is characterized by dispersing a powder in a foam constituting the fugitive model.

In order to disperse the sulfur powder in the foam, the unfoamed raw material of the fugitive model and the sulfur powder may be mixed and the mixture may be foamed. In this case, the mixing ratio of sulfur powder to the model raw material may be 2 to 10% by weight, and it is preferable that 400 to 2.000 mg of sulfur be dispersed per 1 ρ of model volume. The model raw materials may be those conventionally used, and the fugitive model itself can be manufactured by a conventional method.

In order to further enhance the effect, the fugitive model of the present invention may contain boric acid (H, BO41, ammonium borofluoride (N) 1.BF,), etc., in addition to the sulfur powder.

Effects> The vanishing model configured as described above has the following effects. When the molten Mg alloy comes into contact with the sulfur powder in the model, the sulfur powder burns and generates S02 gas. The surface of the molten Mg alloy reacts preferentially with SO2 gas, and Mg is deposited on the surface.
Generate gzS film. This film is formed when the molten Mg alloy is poured and before it touches the sand mold. Therefore, the molten Mg alloy does not come into direct contact with the sand mold, but comes into contact through the Mg*S film, so that reaction between the molten Mg alloy and the sand is prevented.

<Examples> Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

First, the method for manufacturing the evanescent model of this example will be explained.

Ethyl alcohol was added to the sulfur powder and stirred to form a slurry with an appropriate viscosity. Approximately 10% by volume of this slurry-like material is added to polystyrene beads and mixed by stirring.The mixed polystyrene beads are then placed in a foaming machine according to a conventional method and foamed at approximately 80°C to form a predetermined shape with no fussability. I got the model.

As shown in FIG. 1, inside the fugitive model 3 thus obtained, the instant powder 2 was fixed in a dispersed state at the grain boundaries of the polystyrene foam particles 1.

Next, a method for manufacturing Mg alloy castings using this fugitive model will be explained.

As shown in FIG. 2, the above-mentioned fugitive model 3 was placed and fixed in a mold 5 by means not shown, and dry sand was poured onto it to produce a sand mold 4.

Next, in order to prevent the sand from deforming, a V process was applied to maintain the shape of the sand mold 4. That is, a film was pasted on the top surface of the sand mold 4 to prevent air permeability, and at the same time, exhaust air was evacuated from the bottom surface of the sand mold 4 by means not shown, thereby reducing the pressure inside the sand mold 4.

Next, a molten Mg alloy at about 700° C. was poured into the sand mold 4.

When the molten Mg alloy came into contact with the fugitive model, it melted the fugitive model and at the same time burned the sulfur powder to generate SO2 gas. The molten Mg alloy was filled into the sand mold within approximately 10 seconds. After the solidification of the molten Mg alloy is completed, the reduced pressure is released and the sand is removed, leaving a clean Mg surface.
An alloy casting was obtained.

<Effects of the Invention> As is clear from the above explanation, the vanishing model of the present invention has the following effects:
Because it is a fugitive model with an effective powder dispersed in the foam that suppresses unfavorable reactions between the molten Mg alloy and the sand mold,
Beautiful Mg with improved casting surface by using it
Alloy castings can be produced.

Moreover, since the evanescent model of the present invention can be mass-produced by mechanization, it is possible to significantly improve production efficiency by combining it with production technology such as the V process described in the above embodiments. Therefore, Mg, which has been little used due to low productivity and high cost,
Alloy sand molds can be used for molded products such as automobile parts.

For example, intake manifolds that are currently made from aluminum alloy can now be made from Mg alloy.
This can contribute to reducing the weight of the engine.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged sectional view showing the internal structure of a fugitive model according to an embodiment of the present invention, and FIG. 2 is a sectional view showing the state in which the fugitive model is used. In the figure: l...Polystyrene foam particles 2 Sulfur powder 3
...Disappearance, sexual model 4kawa sand mold patent applicant
Toyota Motor Corporation

Claims (1)

[Claims] A fugitive model characterized by dispersing sulfur powder in a foam constituting the fugitive model.