JPS6056439A - Gypsum mold for vacuum casting - Google Patents

Abstract

PURPOSE:To obtain good run and a defectless product without casting defects by providing a filter made of a refractory material having better air permeability than gypsum from the part near the final filling part of the molten metal in the product cavity to the outside surface of a gypsum mold for casting. CONSTITUTION:A filter 5 formed of a refractory material is directly communicated with and provided to the neighborhood of the part in a product cavity 3 where a molten metal is finally filled. The filter 5 is required to have better air permeability than gypsum and is formed preferably of a refractory material. A sand mold or porous zirconia sintered body or the like is usable as the filter 5 meeting such requirements.

Description

[Detailed description of the invention] The present invention relates to a gypsum mold for vacuum casting.

In general, gypsum molds made of non-foamed gypsum (hereinafter simply referred to as molds) have extremely poor air permeability compared to sand molds and the like. For this reason, if the product you are trying to cast is large and the mold is thick,
Furthermore, when casting thin-walled products or parts with complex shapes, poor hot water circulation and gas defects were likely to occur.

Conventionally, therefore, the above-mentioned casting defects have been dealt with by reducing the pressure inside the mold. This vacuum casting method includes a method in which the pressure is reduced through a blind hole. This method improves the pressure reduction effect, and by adjusting the pressure reduction position and degree of pressure reduction, the water circulation becomes better. However, there were problems such as vacuum casting using a mold with blind holes.

In addition, as a method to improve the air permeability of the mold, there is a method of using foamed plaster with good air permeability such as Hydroperm.
The problem with molds made of foamed gypsum is that they are weak in strength.

Furthermore, in any of the above conventional methods, if the product to be cast is thin and has a complicated shape, there is a problem in that the flowability of the hot water is poor and even when the hot water flows, gas defects are generated.

The present invention was made in order to solve the problems of the prior art described above, and provides a gypsum mold for vacuum casting with improved exhaust capacity of the product cavity, which enables thin-walled and complex-shaped products to be vacuum-cast without any casting defects. The purpose is to provide.

According to the present invention, the object is to provide a gypsum mold in which a casting plan cavity such as a sprue and a product cavity are formed, and from the vicinity of the final filling part of the molten metal in the product cavity to the outer surface of the gypsum mold, This is accomplished by using a vacuum casting plaster mold with a filter made of a refractory material that has better air permeability than plaster.

According to the present invention, the above object is a gypsum mold in which a casting plan cavity such as a sprue and a product cavity are formed, and a sump communicating with the product cavity is provided near the final filling part of the product cavity with molten metal. This is achieved by using a gypsum mold for vacuum casting, which is provided with a cavity and a filter made of a refractory material, which has better air permeability than gypsum, extending from the sump cavity to the outer surface of the gypsum mold.

According to the Kawaishi/Ba mold for vacuum casting according to the present invention, the filter made of a refractory material with good air permeability is directly connected to the product cavity.
Alternatively, since it directly communicates with a water reservoir cavity that is provided in communication with the product cavity, the pressure reduction effect when the pressure is reduced through the filter in a normal manner is significantly greater than in the past.

Therefore, due to such a depressurizing effect, the melt poured into the mold of the present invention will spread to every corner of the product cavity, and there will be no problem in the flow of the melt even for complex-shaped parts. Since such air is sufficiently exhausted, there is an effect that gas defects due to the entrainment of such air do not occur.

Next, a description will be given with reference to a drawing of a gypsum mold for vacuum casting according to the present invention.

FIG. 1 is a sectional view of a gypsum mold for vacuum casting according to the first invention of the present invention, and FIG. 2 is a sectional view of a gypsum mold for vacuum casting according to the second invention of the invention.

In Figure 1, 1 is the upper mold, 2 is the lower mold, and ``2 mold 1''
and lower mold 2 into product cavity 3 and product cavity 3? 8. A casting plan cavity 4 is formed to guide the molten metal. In this product cavity 3, a filter 5 made of a refractory material is provided in direct communication with the vicinity of the part that will be the final filling part of the molten metal.

The filter 5 needs to be installed at or near the part of the product cavity 3 that will be filled with molten metal last.

Further, the filter 5 needs to have better air permeability than plaster. The better the air permeability is, the better, but the air permeability is required to be such that the molten metal cannot easily infiltrate into the filter 5. In addition, since this filter 5 comes into direct contact with the molten metal,
It is undesirable to use a material that burns due to the heat of the molten metal or reacts with the molten metal, and is preferably made of a fire-resistant material.

A sand mold, a porous zirconia sintered body, or the like can be used as the filter 5 that does not meet the requirements for bending.

The filter 5 is attached to the mold by embedding it at the same time when the mold is made of plaster, but after the filter 5 cavity is formed and the mold is made, the filter 5 is installed in this cavity.
This is done by a method such as press-fitting and fixing.

Next, FIG. 2 will be explained.

The difference between FIG. 2 and FIG. 1 is that a pool cavity 6 is formed near the final filling part of the product cavity 3 with molten metal, communicating with the product cavity 3; A filter 5 is attached in communication.

As shown in Fig. 2, the mold forming the sump cavity 6 is
During vacuum casting, the flow of molten metal does not stop at the final filling part of the product cavity 3, and for a while it flows into the pool cavity 6.
Therefore, the flowability of the hot water is improved (and gas entrainment is also reduced) compared to the mold without the sump cavity 6 shown in Fig. 1.

In order to carry out vacuum casting using such a plaster mold, except for the vacuum 1" 7 part where the filter 5 is in contact with the outside air, cover the rest with a sealing means such as aluminum foil 8, and also place the filter 5 in the vacuum 1 core. A chamber member or plug connected to a pressure reducing means such as a vacuum pump is attached to the chamber member. After reducing the pressure in the entire stone mold, the metal is poured into the sprue over the aluminum foil.

Next, an embodiment of the present invention will be described.

EXAMPLE Using the plaster mold of the present invention shown in FIG. 2, attached parts were attached as shown in FIG. 3, and vacuum casting was performed.

In FIG. 3, parts or components that are substantially the same as those in FIG. In this example, the wall thickness is 3.5±
A 0.5 mm cover-shaped part was manufactured. Further, as the filter 5, a sand (CO,) type was used.

After forming the plaster mold shown in FIG. 2, the filter 5 was covered with aluminum foil 8 except for the area near the vacuum lower protruding from the mold surface. Further, the vicinity of the vacuum lower was covered with a chamber member 9, and the boundary between the aluminum foil 8 and the chamber member 9 was sealed to prevent vacuum leakage, resulting in the state shown in FIG. 3.

Next, by operating a vacuum pump (not shown), the pressure inside the mold is reduced to a predetermined pressure, and while maintaining this reduced pressure state, JIS AC4 is applied from the direction of arrow A in Fig. 3.
The molten aluminum of C was poured. This pouring melted the aluminum foil, and the molten metal flowed from the casting plan cavity 4 such as a sprue into the product cavity 3 and the sump cavity 6, and stopped at the filter 5.

This experiment was conducted with the degree of pressure reduction set at four levels, and the hot water circulation situation was investigated.

Comparative Example 1 As a first comparative example, as shown in FIG.
A cover-shaped part was vacuum-cast in the same manner as in the example using a conventional mold in which a mold 0 was provided close to the product cavity 3. Note that the chamber member 9 is provided in both the upper mold 1 and the lower mold 2.

Comparative Example 2 In the first comparative example, a cover-shaped part was vacuum-cast under substantially the same conditions as the first comparative example, except that the gas vent hole 10 was provided only in the lower mold.

Table 1 shows the results of an investigation of the running conditions of the castings cast according to the above Examples and Comparative Examples.

Table 1 (Atmospheric pressure: Qmmmm1l Filling rate (wt%)) As is clear from Table 1, when vacuum casting is performed using the plaster mold according to the present invention, when using a conventional mold, In comparison, extremely high water running performance can be obtained.Moreover, atmospheric pressure -5
Even with a low degree of vacuum of 0 mm and 11 g, the hot water runs well. This good running property means that the molten metal speed is high, which leads to a reduction in the pouring height, a corresponding reduction in the size of the mold, and an improvement in the casting yield.

Furthermore, since the exhaust capacity inside the cavity is high, gas defects caused by air in the cavity and air entrainment during pouring can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a gypsum mold for vacuum casting according to the first invention of the present invention, FIG. 2 is a cross-sectional view of a gypsum mold for vacuum casting according to the second invention of the present invention, and FIG. A sectional view of a gypsum mold for vacuum casting used in an embodiment of the invention. FIGS. 4 and 5 are sectional views of a vacuum casting apparatus using a conventional gypsum mold for vacuum casting. ■-・-Upper mold (gypsum mold) 2-Lower mold (Ark mold) 3--Product cavity 4--Casting plan cavity 5--Filter 6=-Sump cavity 7- Decompression 1-1 8- Aluminum 715 9--Chamber Part 10-Gas 1 Friendship Hole Applicant Toyota Motor Forest Ceremony Right No. 1 Diagram 2 Diagram 4 Diagram 7

Claims (1)

[Scope of Claims] fil A gypsum mold in which a casting plan cavity such as a sprue and a product cavity are formed, and the area from the vicinity of the final filling part of the molten metal in the product cavity to the outer surface of the gypsum mold has better air permeability than plaster. A gypsum mold for vacuum casting, characterized by being provided with a filter made of a good refractory material. (2) A gypsum mold in which a casting plan cavity such as a sprue and a product cavity are formed, and a sump cavity that communicates with the product cavity is provided near the final filling part of the molten metal in the product cavity, and the sump cavity is connected to the product cavity. A gypsum mold for vacuum casting, characterized in that a filter made of a fireproof material having better air permeability than gypsum is provided over the outer surface of the gypsum mold.