JP3115384B2 - Low pressure casting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low pressure casting method and apparatus.

[0002]

2. Description of the Related Art A low-pressure casting method is a casting method in which a molten metal is pressed into a mold at a low pressure. That is, in low-pressure casting, generally, a mold having a cavity formed therein, and a melting furnace provided below the mold and filled with a molten metal,
A lower end portion is immersed in the molten metal in the melting furnace, and a conduit that communicates the furnace space with the cavity in the melting furnace is used to pressurize the furnace space. After the melt is filled in the cavity, the pressurized state is maintained for a predetermined time.

[0003]

In the conventional low-pressure casting method described above, when the cavity is filled with the molten metal, a back pressure is generated in the cavity, and this back pressure has an adverse effect on the run-off performance.

On the other hand, Japanese Utility Model Application Laid-Open No. 63-25250 discloses that the cavity of a mold is connected to a vacuum source, and the cavity is brought into a negative pressure state, whereby the molten metal in the melting furnace is sucked into the mold and casting is performed. A suction casting method to be performed is disclosed.

[0005] If such a suction casting method is employed, it is possible to improve the meltability, but the pressurization of the molten metal filled in the cavity is insufficient, so that a cavity is formed inside the casting. There was a problem that it became easier.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a low-pressure casting method and apparatus capable of suppressing the occurrence of cavities in a casting and improving the runnability. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION A low pressure casting method and apparatus according to the present invention achieves the above object by appropriately combining pressurization of a furnace space and depressurization of a cavity. .

That is, the low-pressure casting method according to the present invention comprises:
As described in claim 1, a mold having a cavity formed therein, a melting furnace provided below the mold and filled with a molten metal, and a lower end portion immersed in the molten metal in the melting furnace. And a conduit for communicating between the furnace space of the melting furnace and the cavity, and performing low-pressure casting, wherein the cavity is maintained at a constant negative pressure.
By pressure the furnace space while reducing the pressure in, and the furnace space
Pressure at the molten metal surface position of the cavity
When the horizontal cross-sectional area is small according to the change in the horizontal cross-sectional area
By controlling to be smaller than when large , filling the cavity with the molten metal in the melting furnace,
Thereafter, the depressurization is stopped and the pressurized state is maintained for a predetermined time.

According to a second aspect of the present invention, there is provided a low-pressure casting apparatus comprising: a mold having a cavity formed therein; a melting furnace provided below the mold and filled with a molten metal; A conduit is provided such that the lower end is immersed in the molten metal in the melting furnace, a conduit that communicates the furnace space of the melting furnace with the cavity, and a cover that hermetically covers the mold,
Depressurizing means for decompressing the cavity together with the space in the cover, pressurizing means for pressurizing the furnace space, and depressurizing the cavity at a constant negative pressure by the depressurizing means. the under pressure the furnace space in a pressurized means,
And melt the pressurization against the furnace space of the key Yabiti
The horizontal cross-sectional area according to the change of the horizontal cross-sectional area at the surface position
So that when is small, it is smaller than when it is large
Control means for filling the cavity with the molten metal in the melting furnace, thereafter stopping the decompression by the decompression means and maintaining the pressurized state by the pressurization means for a predetermined time. It is characterized by the following.

[0010]

As described above, according to the present invention, the state in which the cavity is maintained at a constant negative pressure is provided.
Vacuum while the by pressurizing the furnace space, since the molten metal in the melting furnace is adapted to fill the cavity, when filling the molten metal, from the furnace space from the back pressure in the cavity is generated It can be prevented by pressurization , which can improve the meltability. Moreover,
When pressurizing the furnace space, the amount of pressurization is
Control according to the change in the horizontal cross-sectional area at the molten metal surface position,
When the horizontal cross-sectional area is small,
Since the pressure is controlled to be small,
Improves casting quality by maintaining the rate of rise of molten metal at a constant
Can be In addition, after the molten metal is filled, the depressurization is stopped and the pressurized state is maintained for a predetermined time, so that the molten metal filled in the cavity can be sufficiently pressurized. In addition, it is possible to minimize the occurrence of cavities inside the casting, and the structure of the casting can be densified.

Therefore, according to the present invention, it is possible to suppress the occurrence of cavities in the casting and to improve the meltability, thereby obtaining a casting of good quality.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a side sectional view showing one embodiment of a low pressure casting apparatus according to the present invention.

This low pressure casting apparatus has a cavity 1 inside.
2, a melting furnace 18 provided below the casting mold 14 and filled with a molten metal (aluminum molten metal) 16, and a lower end portion immersed in the molten metal 16 in the melting furnace 18. A conduit 22 is provided and communicates the furnace space 20 and the cavity 12 of the melting furnace 18, a cover 24 for airtightly covering the mold 14, a decompression means 28 for depressurizing a space 26 in the cover 24, a furnace space By pressurizing the furnace space 20 with the pressurizing means 30 while depressurizing the cavity 12 with the depressurizing means 28,
A pressurizing / depressurizing controller 32 (control means) for filling the cavity 12 with the molten metal 16 in the melting furnace 18 and thereafter stopping the depressurization by the depressurizing means 28 and maintaining the pressurized state by the pressurizing means 30 for a predetermined time. Has become.

The mold 14 has a space 2 in the cover 24.
A plurality of thin air holes are formed so as to communicate the cavity 6 with the cavity 12, and the pressure reducing means 28 reduces the pressure of the cavity 12 together with the space 26 in the cover 24 through these air holes.

The depressurizing means 28 comprises a vacuum pump 34 and a depressurizing valve stand 36, and the pressurizing means 30 includes a pressurized air source 38 and a pressurizing valve stand 4
It consists of zero. The pressurizing and depressurizing control by the pressurizing and depressurizing controller 32 is performed on the depressurizing valve stand 36 and the pressurizing valve stand 40.

The pressure in the furnace space 20 of the melting furnace 18 is
The pressure is detected by the pressure sensor 42, and the detection signal is input to the pressure increase / decrease controller 32. Further, the pressure in the space 26 in the cover 24 (therefore, the pressure in the cavity 12) is detected by the differential pressure sensor 44 as a pressure difference from the pressure in the furnace space 20.
The data is input to the pressurizing / depressurizing controller 32. The pressurizing / depressurizing controller 32 controls the cavity 1
2 and the amount of pressure applied to the furnace space 20 are controlled in accordance with the differential pressure.

The pressurizing / depressurizing controller 32 controls the amount of pressure reduction in the cavity 12 and the amount of pressurization in the furnace space 20 in accordance with a change in the horizontal sectional area at the position of the molten metal surface of the cavity 12. . To perform such control, molten metal sensors 46A, 46B, and 46C are provided at three locations on the inner surface of the mold 14, respectively. The molten metal sensor 46A is provided at a position where the horizontal sectional area sharply decreases due to the rise of the molten metal.
Is provided at a position where the horizontal sectional area is rapidly increased by the rise of the molten metal, and the molten metal sensor 46C is provided at a position where filling of the molten metal into the cavity 12 is completed.

On the inner surface near the lower end of the side wall of the cover 24, an aluminum piece 48 applied with 12V is attached.

Next, the operation of this embodiment will be described with reference to the time chart of FIG. In the low pressure casting, first, the pressure reducing valve stand 36 is
To reduce the pressure of the cavity 12 together with the space 26 in the cover 24, raise the molten metal 16 in the melting furnace 18 to the inlet of the cavity 12, and then pressurize the pressure while maintaining the cavity 12 at a constant negative pressure. The cavity 16 is filled with the molten metal 16 in the melting furnace 18 by opening the valve of the stand 40 and pressurizing the furnace space 20.

At the time of filling the molten metal, in order to improve the quality of the casting, it is desirable to keep the molten metal rising speed constant. Therefore, the amount of pressure applied to the furnace space 20 is controlled according to the change in the horizontal cross-sectional area at the position of the molten metal surface of the cavity 12 as follows. That is, immediately after the start of the filling of the molten metal, the horizontal cross-sectional area at the molten metal surface position of the cavity 12 is large, so that the pressure is applied with a large pressurization amount (line a). When the molten metal rises, the pressure is increased by a small amount (line b). When the molten metal sensor 46B detects the molten metal due to the rise of the molten metal, the horizontal sectional area is increased. Pressurization is carried out with this large amount of pressure until 46C detects the molten metal.

Thereafter, the depressurization of the cavity 12 is stopped, the pressurized state of the furnace space 20 at a constant pressure is maintained for a predetermined time, and then the pressurized state is released.

As described in detail above, according to this embodiment,
By pressurizing the furnace space 20 while depressurizing the cavity 12, the molten metal 16 in the melting furnace 18 is removed from the cavity 12.
When the molten metal 16 is filled , it is possible to prevent the back pressure from being generated in the cavity 12, thereby improving the run-out performance. Also, after filling the molten metal, the decompression is stopped and the pressurized state is maintained for a predetermined time.
The pressurization of the molten metal filled in the cavity 12 can be sufficiently performed, and the riser action can minimize the occurrence of cavities inside the casting, thereby densifying the structure of the casting. Can be.

Therefore, according to the present embodiment, it is possible to improve the meltability while suppressing the occurrence of cavities in the casting, thereby obtaining a casting of good quality.

During the low-pressure casting, if the molten metal 16 filled in the cavity 12 leaks from the mating surface of the mold 14 into the space 26 in the cover 24 and fills the space 26, the casting machine The mold 14 will be damaged. However, in this embodiment, the cover 2
Since the aluminum piece 48 applied to 12 V is attached to the inner surface near the lower end of the side wall of the molten metal 16
Leaks into the space 26 in the cover 24, the molten metal 16
(Aluminum) makes the aluminum piece 48 conductive. In the present embodiment, the pressurizing / depressurizing controller 32 releases the depressurization of the cavity 12 and the pressurization of the in-furnace space 20 on the assumption that an abnormality has occurred due to the conduction, and stops the casting. Therefore, according to the present embodiment, it is possible to prevent the casting machine and the mold 14 from being damaged due to molten metal leakage.

In addition to the above configuration, as shown in FIG. 3, an opening 24a is formed near the lower end of the side wall of the cover 24, and a zinc plate 50 (low melting point member) is attached to the side wall to open the opening. The portion 24a may be closed. By doing so, the temperature of the molten metal 16 (aluminum molten metal) becomes 6
Since the melting point of the zinc plate 50 is 419 ° C. while the temperature is 20 ° C., when the molten metal 16 hits the zinc plate 50, the zinc plate 50 is melted and the opening 24a is automatically opened. . The opening of the opening 24a prevents the cavity 12 from being depressurized. Based on this, the pressurizing / depressurizing controller 32 can perform control to stop the casting assuming that an abnormality has occurred. Reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing one embodiment of a low pressure casting apparatus according to the present invention .

FIG. 2 is a time chart showing the operation of the embodiment .
You.

Figure 3 is a partial side sectional view showing a modification of the embodiment
You.

[Explanation of symbols]

 Reference Signs List 12 cavity 14 mold 16 molten metal 18 melting furnace 20 furnace space 22 conduit 24 cover 24a opening 26 space 28 depressurizing means 30 pressurizing means 32 pressurizing and depressurizing controller 32 (control means) 50 zinc plate (low melting point member)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-245955 (JP, A) JP-A-64-15260 (JP, A) Japanese Utility Model Showa 57-37559 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) B22D 18/04 B22D 18/08

Claims (3)

(57) [Claims] A mold having a cavity formed therein;
A melting furnace which is provided below the mold and is filled with the molten metal; and a conduit which is provided so that a lower end portion is immersed in the molten metal in the melting furnace and communicates a furnace space of the melting furnace with the cavity. When a method of performing low-pressure casting using a while the pressure was reduced to a state of holding said cavity to a constant negative pressure, to pressure the furnace space, and for the furnace space
Horizontal section at the molten metal surface position of the cavity
Large when the horizontal cross-sectional area is small according to the change of the product
By controlling the pressure to be smaller than the time, the molten metal in the melting furnace is filled into the cavity, and thereafter, the depressurization is stopped and the pressurized state is maintained for a predetermined time. Casting method. 2. A mold having a cavity formed therein, a melting furnace provided below the mold and filled with a molten metal, and a lower end immersed in the molten metal in the melting furnace. A conduit communicating between the furnace space of the melting furnace and the cavity; a cover that hermetically covers the mold; a decompression unit that decompresses the cavity together with the space in the cover; and a pressurization that pressurizes the furnace space. Means, the cavity was maintained at a constant negative pressure by the pressure reducing means
While reducing the pressure on the state, the aforementioned pressure <br/> pressure the furnace space pressurizing means, and said pressurization for furnace space cavity
In accordance with the change in the horizontal cross-sectional area at the molten metal surface position
When the cross-sectional area is small, it becomes smaller than when it is large
Control means for filling the cavity with the molten metal in the melting furnace, thereafter stopping the decompression by the decompression means and maintaining the pressurized state by the pressurization means for a predetermined time. A low-pressure casting apparatus characterized by comprising: 3. The low pressure casting apparatus according to claim 2, wherein an opening is formed in a side wall of the cover, and the opening is closed by a low melting point member.