JP2016132016A - Low-pressure casting method and low-pressure casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-pressure casting method and a low-pressure casting apparatus capable of reducing the generation of gas due to heat of molten metal even if a conventional core formed by shell molding is used, preventing the occurrence of a gas defect or a shrinkage cavity, and facilitating storage of the core.SOLUTION: A low-pressure casting method comprises: installing a core in a casting mold; closing the casting mold; and, before filling molten metal, supplying heating air into the casting mold, sucking a cavity, and drying the core up to an interior thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a low pressure casting method and a low pressure casting apparatus, and more particularly to a low pressure casting method and a low pressure casting apparatus that can prevent gas defects.

  The molten metal discharged from the melting furnace has high cleanliness by removing inclusions such as hydrogen gas, oxides, and intermetallic compounds by flux treatment and degassing treatment. However, in the low pressure casting method, it is inevitable that the molten metal comes into contact with air during the casting operation, and the cleanliness of the molten metal gradually decreases.

Also, if moisture or resin contained in the core installed in the mold is vaporized by the heat of the molten metal, it remains as bubbles inside the molded product (casting), causing gas defects or shrinkage. As a result, the quality of the molded product deteriorates.
In particular, moisture is a source of hydrogen gas that causes the molded product to become hydrogen embrittled, and in order to improve the quality of the molded product, it is important to remove moisture and the like that generate gas by the heat of the molten metal from the mold.

  However, the moisture is also contained in the air, and air enters the mold as the mold is opened. Further, in order to prevent the core installed in the mold from containing moisture, it is necessary to store the core in a humidity-controlled room, which requires a large amount of cost for storing the core.

Although not related to low-pressure casting, in Patent Document 1, in the method in which hot air is fed into the molten metal injection cavity and the sand mold is dried, the water that can be removed is only the surface layer of the sand mold, so an adsorbent such as zeolite or ALC is used. It is disclosed to use.
That is, it is disclosed that the casting sand forming the mold is surrounded by an adsorbent such as zeolite or ALC, and moisture is adsorbed and removed to the inside of the casting sand by the adsorbent. In addition, when using a core, it is described that a core is formed by a sand mold formed of cast sand, an adsorbent embedded in the sand mold, and a reinforcing bar embedded in the adsorbent. Yes.

  However, in the method described in Patent Document 1, an adsorbent having a limit on the amount of adsorption is used, and it is necessary to store the mold so that it does not absorb more moisture than the amount of adsorption of the adsorbent. The core provided with the adsorbent has man-hours for production.

The present invention has been made in view of such problems of the prior art. The purpose is to reduce the generation of gas due to the heat of the molten metal even when using a core containing a resin formed by the shell mode method, and prevent the generation of gas defects and shrinkage cavities and the storage of the core. It is an object of the present invention to provide a low-pressure casting method and a low-pressure casting apparatus that facilitate the above.

  As a result of intensive studies to achieve the above object, the present inventor, in the low-pressure casting method, after the core is installed in the mold and the mold is closed, before the molten metal is filled, heated air is injected into the mold. By supplying and further sucking the inside of the cavity, it was found that the inside of the core could be quickly dried, and that the above object could be achieved, and the present invention was completed.

  The present invention is based on the above knowledge, and the low-pressure casting method of the present invention is such that a core is placed in a mold, the mold is closed, heated gas is supplied into the mold, and the cavity is sucked into the cavity. It is characterized in that the molten metal is filled.

  The low-pressure casting apparatus of the present invention includes a core that forms a cavity together with a mold, a heated gas supply device that supplies heated gas into the mold, and a suction device that sucks the cavity. A core is placed in the mold, the mold is closed, a heated gas is supplied into the mold, the inside of the cavity is sucked, and the cavity is filled with molten metal.

  According to the present invention, the heating gas is supplied into the mold before filling with the molten metal, and the inside of the cavity is further sucked, so that the core is dried by the supply of the heating gas, and gas such as water vapor is generated. Further, the gas generated from the resin or the like contained in the core by suction in the cavity is also discharged from the cavity. Therefore, the occurrence of gas defects and shrinkage can be prevented. In addition, it is not necessary to dry the core in advance, and the core can be stored easily.

It is the schematic which shows an example of the low pressure casting apparatus of this invention. It is the schematic which shows another example of the low pressure casting apparatus of this invention. It is the schematic which shows an example of the casting process of the low pressure casting apparatus of this invention. It is the schematic which shows an example of the timing of the pressurization of a holding furnace, and the drying in a cavity.

The low-pressure casting method and low-pressure casting apparatus of the present invention will be described in detail.
In the present invention, a core is placed in a mold, the mold is sealed, and the mold is used as a drying container for the core. A heated gas is supplied into the mold to dry the core, and the cavity is filled with molten metal to be solidified. Before the casting process, the cavity is sucked and the gas generated from the core is discharged and cast.

Drying of the core starts from the surface, and when the moisture content on the surface decreases, moisture moves to the surface from the portion having a high moisture content inside and evaporates on the surface. By repeating these evaporation and movement, the drying proceeds to the inside.
Accordingly, the faster the moisture moves from the high moisture content portion to the low moisture content, the faster the drying. That is, the greater the difference in water vapor partial pressure and the higher the core temperature, the faster the drying rate.

In the low-pressure casting method of the present invention, in combination with the heat of the molten metal being supplied into the mold via the stalk, the heated gas is supplied into the mold, so the temperature of the core rises rapidly, Water evaporates from the core surface. And since the evaporated water vapor is immediately discharged out of the mold to suck the cavity, the amount of water vapor is kept in the vicinity of the core surface. The inside of the child can be quickly dried.
Therefore, the casting time (cycle time) due to drying of the core does not increase, and in addition, it is not necessary to adjust the amount of water contained in the core in advance, and the core can be easily stored.

FIG. 1 shows a cross-sectional view of an example of the low-pressure casting apparatus of the present invention. In the low-pressure casting apparatus 1, the lower end of the stalk 4 is immersed in the molten metal 3 in the holding furnace 2 that is hermetically sealed, and the gate 5 is provided at the upper end.
A separable mold 6 is disposed on the holding furnace 2, and a core 8 positioned by a base board 7 is accommodated in the mold 6. A cavity 9 is formed by the mold 6 and the core 8. It is formed. The mold 6 may be entirely covered with a chamber (not shown).
The holding furnace 2 is provided with a pressurizing device 10, and an inert gas such as carbon dioxide is pumped or exhausted into the holding furnace 2 to adjust the pressure in the holding furnace, and the molten metal 3 enters the cavity 9 through the stalk 4. Fill. The pressurizing device 10 includes a pressurizing pump, a valve, a pressure sensor (not shown), and the like.

  The mold 6 is connected to a heated gas supply device 11 that supplies heated gas into the mold 6 and a suction device 12 that sucks the cavity 9.

  The heating gas supply device 11 includes a gas heating device 13 such as a heater and a blower (not shown). Examples of the blower include a blower, a fan, and a pump.

  The heating gas supplied into the mold 6 may be air with a low water content, but it is preferable to use an inert gas such as carbon dioxide. By using an inert gas, the air that has entered the mold during the installation of the core is replaced with the inert gas, and the generation of oxides caused by the molten metal coming into contact with the air can be minimized. The cycle time can be shortened.

  The suction device 12 includes a valve 14, a vacuum container 15, a vacuum pump 16, etc., and sucks the gas in the cavity 9 and discharges it outside the mold 6. The suction speed can be adjusted by controlling the opening of the valve 14 and the vacuum pump 16.

The heating gas supply device 11 may supply heating gas directly into the cavity as shown in FIG. 1, but as shown in FIG. 2, heating gas is supplied to the porous material 17 of the mold 6. It is preferable that a heating gas is supplied to the core 8 through a baseboard 7 to which the apparatus is connected and the core 8 is fixed.
By supplying the heated gas directly to the core 8, the pressure inside the core is increased by the heated gas, and the water inside the core is vaporized to further increase the pressure inside the core. And the pressure difference between the outside of the core increases. Therefore, since the moisture inside the core moves to the surface, the core can be quickly dried.

  Further, it is preferable that a path for supplying the heating gas from the skirting board 7 is provided in the core 8. By supplying the heating gas through the path, the temperature and pressure not only from the vicinity of the skirting board but also the entire inside of the core rises, and the drying speed of the core can be further improved.

Next, a low pressure casting method using the low pressure casting apparatus will be described.
First, the mold 6 is opened in a state where a predetermined amount of the molten metal 3 is stored in the holding furnace 2, and the core 8 is placed in the mold together with the base board 7 for determining the position of the core 8 in the mold. Close to a dry container for the core.

  If necessary, a powder release agent may be applied to the inner wall of the mold 6 prior to the installation of the core 8. The powder release agent can be applied by a conventionally known coating method such as spray coating. In the present invention, not only the heating gas is supplied into the mold 6 but also the cavity 9 is sucked, so that inclusions such as a powder release agent that has not adhered to the mold 6 can be discharged out of the mold, Can produce high quality castings.

  When the mold 6 is sealed and the heating gas is supplied into the mold 6, the temperature of the core 8 rises due to the heat of the molten metal 3 in the holding furnace and the heat of the heating gas, and moisture from the core surface. Evaporate. When the valve 14 of the suction device 12 is opened and the gas in the cavity 9 is sucked, water vapor evaporated from the core surface is discharged out of the cavity 9. Then, the difference between the moisture content inside the core and the moisture content on the core surface becomes large, the moisture inside the core moves to the surface, the evaporation of moisture is promoted, and the core quickly dries.

  As the core 8 of the present invention, a core using an inorganic binder can be used in addition to a core having a resin binder formed by a shell mode method. A core using an inorganic binder has low adhesive strength and low strength while generating less gas during casting, but in the present invention, the core can be sufficiently dried. Even if it is the core used, sufficient intensity | strength is acquired and generation | occurrence | production of the defect resulting from a core breakage falls.

Examples of the inorganic binder include magnesium sulfate (MgSO ₄ ), sodium carbonate (Na ₂ CO ₃ ), sodium borate (Na ₂ B ₄ O ₇ ), sodium sulfate (Na ₂ SO ₄ ), and the like.

After the core is dried, next, as shown in FIG. 3, the molten metal surface in the holding furnace 2 is pressurized by the pressurizing device 10, and the molten metal 3 is filled into the cavity through the stalk 4. When the molten metal 3 is solidified, the mold 6 is opened and the molded product is taken out.
In the present invention, the moisture in the mold is removed in advance, and the gas generated from the core and the like by the heat of the molten metal 3 is discharged out of the cavity. Nest formation is prevented.

The filling of the molten metal 3 into the cavity is preferably performed while sucking the cavity. The binder of the core 8 may evaporate due to the heat of the molten metal 3, and by sucking the cavity, the behavior of the hot water is stabilized and the occurrence of gas defects and shrinkage cavities is prevented.
In addition, the suction at the time of molten metal filling and the suction at the time of core drying can be performed by the same suction device.

Here, the timing of pressurization of the holding furnace 2 and pressure reduction in the mold 6 will be described with reference to FIG.
In FIG. 4A, A is a step of supplying a heating gas into the mold after the mold 6 is sealed to form a dry container for the core. B is a step of raising the molten metal 3 in the stalk 4 to the gate by the first pressurization in the holding furnace 2. C is a step in which the molten metal 3 reaches the gate 5 and is switched to the second pressurization in which the filling speed is controlled, and the suction of the cavity is started. By sucking the cavity, water vapor evaporated from the core or gas generated by thermal decomposition of the resin is discharged out of the cavity. When the cavity is filled with the molten metal 3, the pressurization of the holding furnace 2 is stopped, and the pressure is maintained until the molten metal 3 is solidified. On the other hand, the suction of the cavity continues for a while even when the mold 6 is filled with the molten metal 3. By continuing the suction, the hot water containing impurities comes out of the mold 6 and the quality of the molded product is improved. D is a step of solidifying the molten metal in the mold 6. When the molten metal 3 is solidified, the pressure in the holding furnace 2 is gradually lowered, the mold 6 is opened, and the molded product is taken out.

FIG. 4B shows an example in which the cavity is sucked while the heated gas is supplied into the mold and the core is dried. By sucking the cavity while supplying the heated gas, the pressure difference between the pressure inside the core and the outside of the core increases, and the core can be dried quickly.
The heated gas may be continued while the molten metal is rising in the stalk 4, but is stopped when the molten metal 3 reaches the gate 5 and starts to flow into the cavity. Even if the molten metal 3 flows in, if the supply of the heating gas is continued, gas defects and shrinkage cavities are caused.

As described above, the low pressure casting apparatus having one molten metal holding furnace has been described as an example. However, the low pressure casting apparatus of the present invention is not limited to this, and the molten metal holding furnace includes two chambers, a molten metal holding chamber and a pressure chamber. Alternatively, the filling control of the molten metal 3 may be performed by an electromagnetic pump.

DESCRIPTION OF SYMBOLS 1 Low pressure casting apparatus 2 Holding furnace 3 Molten metal 4 Stalk 5 Pouring gate 6 Mold 7 Skirting board 8 Core 9 Cavity 10 Pressurization apparatus 11 Heating gas supply apparatus 12 Suction apparatus 13 Gas heating apparatus 14 Valve
15 Vacuum container 16 Vacuum pump 17 Porous material

JP 2014-136245 A

Claims (7)

A core installation process for installing the core in the mold;
A mold closing process for closing the mold;
A casting process in which the cavity in the mold is filled with molten metal and solidified;
A mold opening step for taking out a molded product formed in the casting step, and a low pressure casting method comprising:
A low-pressure casting method comprising a drying step of supplying heated gas into the mold and sucking the inside of the cavity after the mold closing step and before the casting step.
  2. The low-pressure casting method according to claim 1, wherein heating gas is supplied to the core in the mold through a base board for fixing the core. The low pressure casting method according to claim 1 or 2, wherein the cavity is sucked while the cavity is filled with molten metal.
A mold,
A core that forms a cavity with the mold;
A holding furnace for holding molten metal;
A stalk in which the lower end is immersed in the molten metal in the holding furnace and the molten metal is supplied to the cavity;
A pressurizing device that pressurizes the inside of the holding furnace and fills a cavity with molten metal,
A heated gas supply device for supplying a heated gas into the mold;
A suction device for sucking the cavity,
A low-pressure casting apparatus characterized in that after the mold is closed and before the molten metal is filled into the cavity, a heated gas is supplied into the mold and the cavity is sucked.   The low-pressure casting apparatus according to claim 4, wherein the heating gas supply device is connected to a baseboard for fixing the core.   The low-pressure casting apparatus according to claim 4 or 5, wherein the cavity is sucked while the cavity is filled with molten metal.   The low-pressure casting apparatus according to any one of claims 4 to 6, wherein the core is formed of an inorganic binder.

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