JPH034290B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vacuum mold, and particularly to a vacuum mold that facilitates the escape of gas generated from a core etc. during pouring into the mold.

[Prior art]

Generally, a mold is composed of a set of outer molds and, if necessary, a core supported inside the outer mold by a baseboard, and the inner wall surface of the outer mold and the core A casting is made by injecting molten metal produced by an appropriate method into a mold cavity formed between the core and the outer wall surface. As for the outer mold of a vacuum mold, one side of the upper mold or the lower mold is made up of a film-like shielding material adsorbed to the model body on one side, and a film-like shielding material covering the other side. The filling material is filled into a mold flask that is shielded by a mold, and the pressure inside the flask is reduced using a vacuum pump through an air suction pipe disposed within the flask. In such a vacuum mold, all outer surfaces of the filling material in the mold flask, except for the portion that contacts the mold flask, are covered with a shielding material to reduce the pressure and isolate it from the atmosphere. On the other hand, the core constituting the mold is not normally formed in a vacuum mold and contains an inorganic or organic binder, and therefore generates steam and other gases when pouring into the mold. These gases are
At the initial stage of pouring into the mold, the shielding material is released into the mold cavity along with the gas generated by combustion.
As the molten metal enters the mold cavity, a portion of the gas is sucked through the filling material toward the air suction pipe through the small gap where the shielding material near the molten metal level is melted and burned. Thus, when the core is surrounded by molten metal, the gas must be released into the atmosphere from its end face primarily through the baseboard that supports the core within the outer mold.

In this case, in molding methods other than vacuum molding, the end face of the baseboard is usually in direct contact with the atmosphere, so it is easy for gas to escape, but in vacuum molding, the structure and function of the mold flask make it difficult for the baseboard to escape. Usually, the end face of the part is located inward from the mold flask. Therefore, in order to extract this gas, a gas venting groove A is usually formed on the parting surface between the upper and lower outer molds, which leads from the end face of the baseboard to the atmosphere through the upper and lower mold flasks, as shown in Figure 3. establish.

In addition, as a mold effective for degassing the core in a vacuum mold, in Japanese Patent Application Laid-Open No. 116952/1984, a recess is provided in the part of the mold that supports the core baseboard, and the ventilation blocker facing the recess is A mold is disclosed in which the membrane has a large number of gas vent holes. This is because the numerous gas vent holes drilled in the ventilation barrier membrane of the core baseboard support part of the outer mold become blocked when the core baseboard is set on the core baseboard support part of the outer mold. The purpose is to prevent the degassing effect from being diminished due to clogging. Therefore, in this mold, the core can be firmly supported and the gas vent hole will not be blocked when the core is set. Thus, gas generated from the core during pouring is sucked into the outer mold from the recess through the gas vent hole.

[Problem that the invention seeks to solve]

However, according to the inventor's experience, when pouring progresses and the level of the molten metal rises, and the core is surrounded by molten metal, the gas pressure increases at that moment or just before that, and the gas flows into the gas vent groove A. is released to the outside all at once. After that, the pressure of the gas suddenly decreases, and the gas is no longer able to escape to the outside due to the resistance of the gas vent groove A, and on the contrary, the atmosphere passes through the gas vent groove A, and the mold cavity The molten metal is sucked into the filler from the molten combustion part of the shielding material near the molten metal level. Furthermore, in addition to this, due to the instantaneous atmospheric suction effect mentioned above,
Often, the shielding material along this groove A peels off locally from the filling material that is in close contact with it, so that short-circuit suction of the atmosphere through the filling material occurs from the gap created by this peeling. Cheap. For these reasons,
The suction of the gas generated from the core into the suction tube is significantly hindered. As a result of these phenomena, blowholes due to poor degassing occur, especially near the baseboard of the core that serves as the gas passage, and deformation due to the inability of the filler to maintain its shape due to a temporary decrease in the degree of vacuum. This is a cause of defects in casting products such as tension. Further, the gas vent groove A sometimes becomes a cause of leakage.

Furthermore, in the vacuum mold, as mentioned above,
All the outer surfaces of the filling material in the mold flask, except for the part that contacts the mold flask, are covered with a shielding material to reduce the pressure and isolate it from the atmosphere. Therefore, drilling holes in the shielding material that covers the filler before pouring the molten metal will reduce the degree of vacuum in the part of the mold flask close to the hole, causing mold deformation, and will also prevent degassing. This tendency will become even stronger if the number and area of holes are increased. Therefore, it can be said that drilling a large number of gas vent holes in the shielding material before pouring is a technical measure with a very serious flaw that ignores the basic principles of vacuum molding.

[Means for solving problems]

This invention was made to solve the above-mentioned problems, and in particular to provide a new vacuum mold that completely eliminates the need for conventional gas vent grooves and vent holes.
In a reduced pressure mold, a core is supported at its baseboard inside a set of outer molds, and a mold cavity is formed between an inner wall surface of the outer mold and an outer wall surface of the core,
A first cavity for storing a part of the molten metal poured into the mold cavity is provided between an end surface of the baseboard part of the core and a corresponding inner surface of the baseboard support part of the outer mold. and pouring into the mold cavity by communicating the first cavity and the mold cavity between the outer surface of the baseboard part of the core and the inner surface of the baseboard support part of the outer mold. It is constructed by providing a second cavity portion through which a portion of the molten metal is introduced into the first cavity portion.

[Effect]

In the vacuum mold according to the present invention, a portion of the poured molten metal passes through the second cavity, reaches the first cavity provided on the end surface side of the baseboard of the core, and is stored there. Therefore, a considerable portion of the gas generated from the core is dispersed from the gap where the shielding material surrounding the first and second voids is melted and burned by the entrance of the molten metal, and passes through the filler toward the suction pipe. The suction is stable. In particular, since it is usually not necessary to apply a coating to the outer surface and end surface of the baseboard part of the core, it is easy for gas to pass through and escape. Therefore, no sudden increase in gas pressure occurs. Further, since atmospheric air is not sucked from the gas vent groove, the suction of gas generated from the core is not hindered.

〔effect〕

As is clear from the above, in the vacuum mold according to the present invention, the gas vent groove and the gas vent hole can be completely eliminated.
By effectively utilizing the capacity of the vacuum pump for decompression without disturbance, the generated gas is stably sucked through the filling material toward the suction pipe from the first and second voids. Therefore, various casting product defects caused by poor degassing of the core and the application of degassing grooves and degassing holes, i.e., blowholes, filling material in or near the baseboard of the core. It is possible to reliably prevent deformation, tension, and leakage of hot water from the gas vent groove due to changes in the degree of reduced pressure. In addition, intentionally creating a first gap between the end of the baseboard and the outer mold is effective in preventing damage to the core and shielding material when storing the core in the outer mold. It is.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The figure shows the core 3 inside the upper and lower outer molds 1 and 2, supported by the baseboard 3a, and the main parts of the vacuum mold in the state before pouring after completing frame alignment. . Suction pipes 4a, 5a for depressurization, which are connected to a vacuum pump (not shown) via the flasks 4, 5, are appropriately disposed inside the mold flasks 4, 5. A silicic acid filler 6 is filled inside the mold flasks 4, 5, and their inner and outer surfaces are shielded by membrane-like shielding materials 7, 8, 9, and 10 to prevent suction from the suction pipes 4a, 5a. The insides of the frames 4 and 5 are kept in a reduced pressure state, and the outer molds 1 and 2
is configured.

The above is a known configuration of a vacuum mold, but in this embodiment, the end face of the baseboard part 3a of the core 3 and the baseboard support parts 1a, 2a of the outer molds 1, 2 corresponding thereto are
A first gap 11 having a width of about 4 mm is provided between the inner surface of the holder and the inner surface of the holder. In addition, by providing two linear notches with a substantially triangular cross section each side of about 10 mm on the inner circumferential cutout surface of the baseboard support part 1a of the outer mold 1, facing each other in the longitudinal direction of the baseboard support part 1a, A second cavity 12 is formed between the baseboard 3a of the child 3 and the outer circumferential surface of the baseboard 3a, and the first cavity 11 communicates with the mold cavities 1b and 2b through the cavity 12. .

In this embodiment, a part of the molten metal poured into the mold passes through the second cavity 12 and into the first cavity 1.
1. Therefore, even if the core 3 is surrounded by molten metal, a considerable portion of the gas generated from the core 3 is caused by the shielding material being melted by the molten metal flowing into the first and second voids 11 and 12. It is stably sucked into the filler 6 from the burned gap. In addition, since there is no air suction, the mold cavity 1 near the baseboard 3a
The shapes of the fillers b and 2b are maintained stably.
As a result, it is possible to reliably prevent casting defects such as blowholes, deformation, tension, etc. that tend to occur in this area. Furthermore, in this embodiment, there is no need to provide a gas vent groove, and there is no need to damage the shielding material such as drilling the shielding material before pouring, thereby reducing the degree of vacuum in the mold flask. There are no occurrences of various casting defects.

It should be noted that the total surface area of the first cavity 11 and the second cavity 12 in this embodiment is preferably as large as possible from the viewpoint of the escape effect of the generated gas, but it is preferable that the total surface area of the first cavity 11 and the second cavity 12 be as large as possible. It will be limited to a range that does not cause any practical problems.

Regarding the molding of the first cavity 11, when the core 3 is housed inside the outer molds 1 and 2, the shielding material 7,
8 and the core 3, the baseboard part 3a
It is normal to provide a gap with a certain width between the end face of the baseboard support parts 1a and 2a of the outer molds 1 and 2. The object of the present invention can also be achieved by forming the first cavity 11 by providing a gap and allowing the molten metal to flow into the first cavity 11 through the second cavity 12. However, if the width of the first cavity 11 is too large, the yield of the cast product will decrease.

Furthermore, the cross-sectional area of the second cavity 12 is sufficient as long as it allows the molten metal to flow reliably, and the number of the second cavities 12 is one or two.
The number of holes may be larger than 100 mm, and it may be provided on other surfaces than the mold parting surface. However, if the cross-sectional area is too large, it will take more effort to finish the cast product, although the effect remains the same. Second cavity 12
An appropriate shape other than a triangle can also be selected as the cross section. In addition, as a method of forming it, instead of providing it on the baseboard support parts 1a and 2a of the outer molds 1 and 2, it can also be provided on the baseboard part 3a of the core 3. Note that the dimensions of the first and second voids do not directly affect the main body of the cast product, so it goes without saying that strict precision is not required.

[Brief explanation of the drawing]

Fig. 1 is a partial vertical sectional view of a vacuum mold showing an embodiment of the present invention, Fig. 2 is a partial sectional view taken along the - line in Fig. 1, and Fig. 3 is a conventional vacuum mold with a gas vent groove. FIG. Explanation of symbols, 1, 2... Outer type, 1a, 2a...
Baseboard support portion, 1b, 2b... Mold cavity, 3...
Core, 3a... core baseboard part, 4, 5... mold flask, 4a, 5a... suction pipe, 6... filler, 7,
8, 9, 10... Film-like shielding material, 11... First cavity, 12... Second cavity, A... Gas vent groove.

Claims (1)

[Claims] 1. A vacuum mold in which a core is supported inside a set of outer molds at its baseboard, and a mold cavity is formed between an inner wall surface of the outer mold and an outer wall surface of the core. providing a first cavity for storing a portion of the molten metal poured into the mold cavity between the end face of the child baseboard and the corresponding inner face of the baseboard support of the outer mold; and the first cavity and the mold cavity are communicated between the outer surface of the baseboard part of the core and the inner surface of the baseboard support part of the outer mold, and the molten metal is poured into the mold cavity. 1. A vacuum mold, characterized in that a second cavity is provided for introducing a portion of the molten metal into the first cavity.