JPS5916860B2 - Reduced pressure mold casting method - Google Patents

Description

[Detailed Description of the Invention] This invention relates to improving the mold surface in vacuum molding, and attempts to reduce the number of casting defects by locally freezing the vicinity of the cavity defining surface of the mold. It is something.

Generally, in the conventional vacuum mold casting method, molten metal is cast into a vacuum casting mold made by solidifying heat-resistant particles under reduced pressure using a synthetic resin film.

In the case of the lower mold, the molten metal does not vaporize the film, and the molten metal itself is sucked under reduced pressure by replacing the film with the molten metal, and it sticks to the heat-resistant particles, allowing casting to be made without the mold collapsing.

However, in the case of an upper mold, the film is vaporized by the radiant heat of the molten metal, and before the molten metal replaces the film, the heat-resistant particles are exposed and the mold easily loses its shape.

Also, in the lower mold, depending on the vacuum force, the particle size of the heat-resistant particles, the speed of the molten metal, etc., the film in the direction of the flow of the molten metal is vaporized and attracted to the heat-resistant particles, which are exposed.
It tends to cause defects such as sand spots, has poor surface stability, and tends to cause casting defects.

Conventionally, methods for imparting surface stability to such vacuum molding molds include the method of using thermoset extensible refractory particles as molding sand (Japanese Patent Laid-Open No. 21325/74) and the method of applying a solvent solution to the film molding surface. How to wear (Unexamined Japanese Patent Publication No. 5118/74,
No. 64421/76), etc. have been proposed.

However, both require additional coatings and are therefore costly.

Since the hardened layer generates industrial waste after demolding, its disposal becomes a problem.

Also, a method using a frozen mold is known as one of the casting methods, but in this method, it is necessary to freeze the entire mold.

For this reason, when it comes to one large mold, it is difficult to completely freeze the entire mold, and furthermore, if it is frozen at a temperature of 150° C. or higher, the strength of the mold decreases and it becomes unusable as a mold.

This invention was proposed in view of the drawbacks of the conventional vacuum mold casting method and freeze mold casting method as described above. The purpose is to increase the stability of the mold surface by incorporating it and then freezing the core, thereby obtaining a product with a sharp cast surface.

The present invention will be described in more detail below based on the accompanying drawings.

As shown in FIG. 1, a mother die 1 used in the present invention has a hollow portion 10 formed therein, and a mold surface 13 formed on its upper surface.

The hollow part and the mold surface communicate with each other through a plurality of small through holes 11, and a suction port 15 is provided in communication with the hollow part 10.

The suction port is connected to a suction device (not shown).

When the forced film 3 is placed opposite to the mold surface 13 of the matrix 1 having such a structure and vacuum suction is applied to the hollow part 10 using the suction device, the film 3 is brought into close contact along the mold surface 13. .

Next, water 5 is sprayed onto the surface of the film.

Thereafter, as shown in FIG. 2, a frame 2 is assembled on the matrix 1, and heat-resistant particles 4 not mixed with a binder are filled in the frame and vibrations are applied to the frame. and mold it.

Furthermore, in this state, the top surface of the frame is closed with a film 30,
The inside of the frame 4 is vacuum-suctioned through a suction port (not shown) provided in the frame to reduce the pressure and solidify the heat-resistant particles 4.

When the heat-resistant particles are completely solidified, the suction inside the mother mold is stopped and the mold is released as shown in FIG.

Next, by spraying a refrigerant such as liquid nitrogen on the side opposite to the refractory or on the IJ type cavity defining surface and cooling it, the water interposed between the mold cavity defining surface and the film is frozen together with the particles. Frozen layer 5 along the mold cavity defining surface
0 is formed.

The upper and lower molds were manufactured using this method.

As shown in FIG. 4, a predetermined mold 40 is obtained without mold matching, and molten metal is poured into the cavity 7 through a sprue (not shown).

During pouring, the heat-resistant particles in the vicinity of the mold cavity defining surface are bonded together by freezing water, so molten metal does not penetrate between the heat-resistant particles.

In addition, since the above-mentioned bacteria type is depressurized, its thermal conductivity is poor.

Therefore, even if the frozen layer 50 is thin, the bond between the refractory fillers is maintained.

According to such a vacuum mold casting method, casting defects caused by the mold cavity defining surface 7) being roughened by the molten metal during pouring do not occur, making it easy to obtain castings with clean casting surfaces. can.

Furthermore, after pouring, the ice in the frozen layer 50 turns into water and evaporates, so other heat-resistant materials that can be reused after demolding, such as those in which a solvent or the like is applied to the film forming surface to form a hardened layer, may be used. There is no production of industrial waste that requires separation from particulate matter, and since water is used instead of a solvent, the cost is low.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing the molding procedure according to the present invention, FIG. 3 is a cross-sectional view showing the half mold obtained by the above procedure, and FIG.
The figure is a sectional view showing a mold obtained by fitting the above half molds. 1...Mother mold, 2...Frame, 3,30...
····film. 4...Heat-resistant particles, 5...Water, T.
...Cavity, 10...Hollow part, 11
・・・・・・／J＼Through hole.

Claims (1)

[Claims] 1. A film is adsorbed onto a matrix, heat-resistant particles are filled onto the film, and the space between the particles is reduced to solidify. When releasing the mother mold and pouring the metal into the mold to be produced, water is sprayed onto the side surface of the particulate material of the film, the heat-resistant particulate material is filled, the pressure between the particles is reduced, and the mother mold is poured into the mold. The Sekizo method is characterized by cooling the mold after releasing it.