JPH08309509A - Differential pressure molding method - Google Patents

Abstract

PURPOSE: To provide a differential pressure forming method which is difficult to develop internal defect in the whole body and can form a product having small crystal grain diameter. CONSTITUTION: While making the pressure in a second chamber R2 higher than the pressure in a first chamber R1 , the pressure in the first chamber R1 is made to higher than the atmospheric pressure, molten Mg is poured into a cavity 13a against the gravitation. Since the whole molten Mg filled up in the cavity 13a can be pressed at the equal pressure, even if the Mg cast product has a complicate shape, the internal defect is difficult to remain. Further, since the molten Mg filled up in the cavity 13a can be pressed at the higher pressure than the atmospheric pressure, the crystal growth is restrained and the structure having small grain diameter is obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a differential pressure molding method. This differential pressure molding method is suitable for casting Mg or the like.

[0002]

2. Description of the Related Art For example, when casting a cast product, a sand mold consisting of an upper die and a lower die defines a cavity, and the molten metal poured into the cavity casts the cast product. Here, internal defects such as shrinkage cavities are likely to occur in the cast product due to shrinkage of the molten metal during solidification progress. For this reason, in order to prevent the occurrence of such internal defects, it is possible to perform hot water feeding.

As a casting method capable of performing this riser, the gravity casting method of Mg described in Japanese Patent Laid-Open No. 3-124359 is known. In this casting method, one end of the sleeve connected to the inert gas supply device is opened in a part of the cavity, and a part of the molten Mg filled in the cavity is pressed by the high pressure inert gas acting from the sleeve. This is to prevent internal defects.

Further, there is also known a differential pressure casting method including a suction casting method (low pressure casting method) and a suction pressure casting method which utilize the fact that a sand mold defining a cavity has air permeability. Among them, as described in JP-A-61-195770,
As an example of the differential pressure casting method capable of performing hot water,
In this casting method, a sand mold is first provided in a closed chamber, and molten metal is stored below the sand mold. In addition, a stalk that connects the cavity and the molten metal is extended downward from the sand mold. If the pressure in the closed chamber is reduced in this state, the molten metal is filled into the cavity via the stoke against gravity. At this time, there is an advantage that the molten metal can be filled while keeping the molten metal surface stable. Further, when the solidification of the molten metal progresses, a part of the stalk is moved to the cavity side while being pressurized and the molten metal is pushed to prevent internal defects.

[0005]

However, Japanese Patent Laid-Open No. 3-1 is used.
In the casting method described in Japanese Patent No. 24359, only a part of the molten metal filled in the cavity can be pressed, and the casting product has a complicated structure such that a thin portion and a thick portion such as a functional boss are adjacent to each other. In the case of a shape, internal defects are likely to remain particularly in the thick portion far from the pressed portion. In addition, the molten metal filled in the cavity is only pressed by the atmospheric pressure in the parts other than the pressed part, and crystals tend to grow in that part, resulting in a structure with a large grain size. . Here, the crystal grain size of the cast Mg product (μm)
When the relationship between the tensile strength (MPa) and the tensile strength (MPa) was examined, it was revealed that these have an inversely proportional relationship, as shown in FIG. For this reason, there is a concern about mechanical properties such as tensile strength of a cast product having a structure with a large grain size in a part thereof.

On the other hand, the casting method described in Japanese Patent Application Laid-Open No. 61-195770 is also obtained because the molten metal in the cavity is decompressed through the closed chamber, and crystals easily grow in the entire molten metal in the cavity. The entire cast product has a structure with a large grain size, and there is concern about the mechanical properties as a whole. In the other differential pressure casting method in which the molten metal side is pressurized, the molten metal in the cavity is still kept at the atmospheric pressure, and the same is true.

The quality problems of these internal defects and the deterioration of mechanical properties due to a large crystal grain size are applicable not only to cast products but also to other molded products. The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a differential pressure molding method capable of molding a molded product having a small crystal grain size, which hardly causes internal defects as a whole. .

[0008]

The differential pressure molding method of the present invention comprises:
An air-permeable mold that has air permeability and defines a cavity is provided in a closed first chamber, and a liquid material is stored in a closed second chamber below the ventilation mold, and the cavity and the liquid chamber are stored. A preliminary step of extending a stalk communicating with a material downward from the ventilation mold; and a pressure in the first chamber higher than the atmospheric pressure while the second chamber is higher in pressure than the first chamber, And a filling step of filling the liquid material against gravity.

In the differential pressure molding method of the present invention, it is preferable to use a cooled gas when the pressure in the first chamber is made higher than atmospheric pressure. Further, when casting a Mg cast product, it is necessary to use an inert gas such as argon gas or a flameproof gas such as SF _{6 as} a gas, but the first chamber is formed by a conventionally used flameproof hood. Therefore, the design change can be made relatively simple.

[0010]

In the differential pressure molding method of the present invention, in the preliminary step,
An air-permeable type having air-permeability and defining a cavity is provided in the closed first chamber, and the liquid material is stored in the closed second chamber below the ventilation type. In addition, a stalk that connects the cavity and the liquid material is extended downward from the ventilation mold.

Next, in the filling step, the second chamber is made to have a higher pressure than the first chamber and the first chamber is made to have a higher pressure than the atmospheric pressure so that the cavity is filled with the liquid material against gravity. At this time, since the entire liquid-like material filled in the cavity can be pressed at an equal pressure, internal defects are unlikely to remain even if the molded product has a complicated shape. Further, since the liquid material filled in the cavity can be pressed at a high pressure exceeding the atmospheric pressure, crystal growth is suppressed and the structure has a small grain size.

[0012]

EXAMPLES Examples 1 and 2 in which the present invention is embodied in a differential pressure casting method will be described below with reference to the drawings. (Example 1) "Preliminary step" First, the differential pressure casting apparatus shown in Fig. 1 is facilitated. In this differential pressure casting apparatus, the recess 1a is provided in the base 1, and the heat storage body 2 is placed on the bottom surface of the recess 1a.
A burner 3 is provided on the side of the heat storage body 2. In addition,
Instead of the burner 3 or the like, other heating means such as a heater may be adopted. The crucible 4 is housed in the recess 1a with its flange 4a being held by the boss portion of the base 1, and the Mg melt 5 is stored in the crucible 4.

A lid member 6 is placed above the crucible 4, and the lid member 6 and the flange 4a of the crucible 4 are clamped by a clamp member 7, whereby the inside of the crucible 4 is sealed. That is, the second chamber R ₂ is located above the molten Mg 5 in the crucible 4. The crucible 4 for the lid member 6
A gas supply hole 6a that opens inside is formed up to the end, and this gas supply hole 6a is connected to a high-pressure pipe line 8, and the high-pressure pipe line 8 penetrates the clamp member 7 to the outside of the base 1. It has been derived. Further, a through hole 6b is vertically provided at the center of the lid member 6, and an upper end of a stalk 9 whose lower end is immersed in the molten Mg 5 is attached in the through hole 6b.

A sand mold 10 having air permeability is placed on the lid member 6. The sand mold 10 defines a runner mold 11 having a runner 11a communicating with the inside of the stalk 9, a lower mold 12 having a plurality of gates 12a communicating with the runner 11a, and a cavity 13a communicating with the melter 12a. It consists of the upper mold 13. A flame retardant such as sulfur, boric acid or potassium borofluoride is added to the sand mold 10. A weight 14 is placed on the upper mold 13 to prevent the upper mold 13 from floating during casting. A flameproof hood 15 that covers the lid member 6, the sand mold 10, and the like is airtightly fixed to the base 1. That is, the inside of the flameproof hood 15 is the first chamber R ₁ . It should be noted that this flameproof hood 15 has been used conventionally, and its design change was relatively easy. A low pressure pipe 16 that opens to the inside is connected to the flameproof hood 15, and the low pressure pipe 16 is led to the outside.

Outside the base 1, a high pressure valve device 17 is connected to the high pressure pipe line 8, and the high pressure valve device 17 is connected to a gas supply device 19 via a high pressure controller 18. A low pressure valve device 20 is connected to the low pressure pipe 16, and the low pressure valve device 20 is connected to a gas supply device 19 via a low pressure controller 21. The high pressure controller 18 and the low pressure controller 21 are the pressurization control device 22.
The gas supply device 19 is connected to a tank (not shown) filled with argon gas.

"Filling Step" Next, molten Mg is poured into the cavity 13a against gravity. At this time, first, the pressurization control device 22 determines the pressure and the flow rate according to the casting weight and the height of the cavity 13a. Then, based on the signal from the pressurization control device 22, the high pressure controller 18
Controls the high pressure valve device 17. Therefore, the argon gas is supplied from the gas supply device 19 through the high-pressure pipe 8 and the gas supply hole 6a into the second chamber R ₂ , and the inside of the second chamber R ₂ has the first pressure P ₁ higher than the atmospheric pressure. It At this time, the inside of the first chamber R ₁ is still at atmospheric pressure. Therefore, crucible 4
The molten Mg 5 inside is a stalk 9, a runner 11a, and a sprue 12.
It is poured into the cavity 13a via a.

After the molten Mg 5 is completely poured into the cavity 13a (this confirmation is made by the time calculation of the pressurizing controller 22), the pressurizing controller 22 adjusts the weight and the wall thickness of the cast product. The corresponding pressure and flow rate are determined. The high-pressure controller 18 controls the high-pressure valve device 17 based on a signal from the pressure control device 22, argon gas from the gas supply unit 19 is further supplied to the second chamber R _2, the second chamber R ₂ The second pressure P is higher than the first pressure P ₁ inside
It is considered to be ₂ .

At the same time, the low pressure controller 21 controls the low pressure valve device 20 based on the signal from the pressurization control device 22. Therefore, from the gas supply device 19 to the low pressure line 16
Argon gas passed through is supplied to the first chamber R _1, the first chamber R ₁ is higher than the atmospheric pressure, it is lower than the second pressure P ₂ the third pressure P _3. Thus, as shown in FIG. 5, while the second pressure P ₂ is the pressure in the second chamber R ₂ to be higher than the third pressure P ₃ is the pressure in the first chamber R _1, the first chamber R The third pressure P ₃ , which is the pressure within ₁ , is set higher than atmospheric pressure.

At this time, the entire molten Mg poured into the cavity 13a shown in FIG. 1 is pressed to a constant pressure by the third pressure P ₃ by the sand mold 10 having air permeability. Therefore, even if the cast product has a complicated shape, internal defects are unlikely to remain as a whole due to the entire riser. Further, since the Mg melt poured into the cavity 13a can be pressed by the third pressure P ₃ which exceeds the atmospheric pressure, crystal growth is suppressed and the grain size becomes small. (Embodiment 2) In Embodiment 2, when the inside of the first chamber R ₁ is set to the third pressure P ₃ which is higher than the atmospheric pressure, the argon gas is cooled and circulated.

"Preliminary Step" First, the differential pressure casting apparatus shown in FIG. 2 is facilitated. In this differential pressure casting apparatus, a water jacket 23 in which cooling water is circulated around the low-pressure pipe 16 is provided, and a lead-out pipe having an orifice opened inside at a position facing the low-pressure pipe 16 in the flameproof hood 15. The line 24 is connected, and the outlet line 24 is circulated to the gas supply device 19. Since the other configurations are the same as those of the differential pressure casting apparatus of the first embodiment, the same configurations are denoted by the same reference numerals and the description thereof will be omitted.

"Filling Step" Using this differential pressure casting apparatus, molten Mg is poured into the cavity 13a against gravity.
When the pressure in the first chamber R ₁ is set to the third pressure P ₃ as in the first embodiment, the pressurization control device 22 also takes into account the opening area of the orifice in the outlet conduit 23 to calculate the pressurization control device 22.
The low pressure controller 21 controls the low pressure valve device 20 based on the signal from the. Therefore, the argon gas from the gas supply unit 19 is supplied to the first chamber R ₁ is cooled by the water jacket 23, after heat exchange with the sand mold 10, the first chamber R ₁ third pressure P _While being maintained at ₃ , the gas is returned to the gas supply device 19 through the outlet passage 23.

In the Mg cast product, as shown in FIG. 4, the solidification time (second) and the crystal grain size (μm) had a direct proportional relationship. Therefore, it can be seen that if the solidification time is long, a structure having a large particle size is likely to be formed, and a molded product having a structure having a large particle size is concerned about mechanical properties such as tensile strength. In this respect,
In the differential pressure casting method of Example 2, since the argon gas cooled when the pressure in the first chamber R ₁ is made higher than the atmospheric pressure is used, the solidification time of the Mg molten metal is shortened and the grain size is reduced. It can be seen that a Mg cast product having a small structure is obtained, and thus excellent mechanical properties are obtained. (Evaluation) As Comparative Example 1, M was obtained by a general differential pressure casting method.
A cast product was obtained. That is, the sand mold is provided in the closed chamber, and the molten Mg is stored below the sand mold. In addition, a stalk that connects the cavity and the molten metal is extended downward from the sand mold. By depressurizing the closed chamber in this state, the molten Mg is filled into the cavity through the stoke against gravity, and is maintained in this state until the molten Mg solidifies.
In the case of the differential pressure casting method, the Mg molten metal is replenished via the stalk when the Mg molten metal is contracted due to solidification, so that the gentle molten metal is pushed.

Further, as Comparative Example 2, JP-A-61-119
A Mg cast product was obtained by the differential pressure casting method described in Japanese Patent No. 5770. That is, the sand mold is provided in the closed chamber, and the Mg
Store the molten metal. In addition, a stalk that connects the cavity and the molten metal is extended downward from the sand mold. By depressurizing the closed chamber in this state, the molten Mg is filled into the cavity through the stoke against gravity. At this time, when solidification of the Mg molten metal progresses, a part of the stalk is moved to the cavity side while pressurizing and the molten metal is pushed. In the case of the differential pressure casting method, the Mg melt is replenished in a pressurized state via the stalk when the Mg melt contracts due to solidification, and the molten metal is pressed by pressurization.

The tensile strengths of the cast Mg products obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were compared. The results are shown in Table 1.

[0025]

[Table 1] From Table 1, it can be seen that the differential pressure casting method of Examples 1 and 2 can secure a higher tensile strength of the Mg cast product as compared with the cases of Comparative Examples 1 and 2.

The differential pressure molding method of the present invention can be applied not only to Mg castings but also to castings of other metals and resin moldings.

[0027]

As described above in detail, in the differential pressure molding method of the present invention, since the structure described in the claims is adopted, it is possible to obtain a molded product having a small crystal grain size, which is unlikely to cause internal defects as a whole. It can be molded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a differential pressure casting apparatus according to a first embodiment.

FIG. 2 is a cross-sectional view showing a differential pressure casting apparatus according to the second embodiment.

FIG. 3 is a graph showing the relationship between crystal grain size and tensile strength.

FIG. 4 is a graph showing the relationship between solidification time and crystal grain size.

FIG. 5 is a graph showing a relationship between time and pressure according to Examples 1 and 2.

[Explanation of symbols]

10 ... vented (sand mold) 13a ... cavity R ₁ ... first chamber R ₂ ... second chamber 5 ... liquid material (Mg melt) 9 ... Stoke

Claims (1)

[Claims] 1. An air-permeable mold having a gas permeability and defining a cavity is provided in a closed first chamber, and a liquid material is stored in a closed second chamber below the ventilation mold. A preliminary step of extending a stalk that communicates between the cavity and the liquid material downward from the ventilation mold; and a pressure in the second chamber that is higher than that in the first chamber and a pressure in the first chamber that is higher than atmospheric pressure. And a filling step of filling the cavity with the liquid material against gravity, the differential pressure molding method.