JPH03264150A - Method and apparatus for reduced pressure casting - Google Patents

Abstract

PURPOSE:To prevent disturbance of molten metal and the development of oxide by pressurizing the molten metal surface in a furnace and reducing the pressure to the atmospheric pressure after filling up the molten metal into cavity in a mold through a stalk under pressure and then opening the mold under the atmospheric pressure or higher. CONSTITUTION:The pressure is given to the molten metal 12 surface in the furnace 14 through a servo valve 22. The cavity 16 in the mold 18 is filled with the molten metal 12 under this pressure through the stalk 20. In the above low pressure casting method, after the molten metal 12 in the mold 18 solidifies, the pressure on the above molten metal 12 surface is reduced. Under the pressure on this molten metal 12 surface at least higher than the atmo spheric pressure, the mold 18 is opened to take out the casting product. After that, the pressure on the above molten metal 12 surface is reduced to the atmospheric pressure to return the molten metal in the stroke 20 into the furnace 14. Then, both a first and second valves 24, 26 for discharging are arranged to the furnace 14, and after opening the pressure, the pressure on the molten metal 12 surface is reduced at a first pressure reducing speed and after that, it is desirable to reduced the pressure to the atmospheric pressure at a second pressure reduc ing speed faster that the first pressure reducing speed. By this method, the disturbance of molten metal 12 in the furnace 14 and the development of oxide are prevented and starting of leakage of the molten steel can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-pressure casting method and apparatus for filling a cavity in a mold with molten metal and pressurizing it to obtain a cast product by applying fluid pressure on the surface of the molten metal. .

[Prior Art] In low-pressure casting, pressure is applied to the surface of the molten metal in a furnace, and after this molten metal is filled into a cavity in a mold through a stalk and solidified under pressure, the pressure on the surface of the molten metal is reduced. Then, the pressure is reduced to atmospheric pressure and the work of removing the casting is performed. However, because the cavity is sealed, even if the pressure on the surface of the molten metal reaches atmospheric pressure, the molten metal remains in the stalk, and when the mold is opened, the molten metal in the stalk falls into the furnace, causing the molten metal to explode. This will lead to disturbance. In particular, if the distance between the molten metal in the furnace and the molten metal in the stalk becomes large, the above-mentioned disturbance becomes significant, and a large amount of oxides are generated and gases are mixed in.

Therefore, a method has been proposed in which the molten metal in the stalk is prevented from falling into the furnace by constantly applying a pressure slightly higher than atmospheric pressure to the surface of the molten metal in the furnace. (See Publication No. 29448).

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the molten metal always remains in the stalk, so the temperature of this molten metal decreases and it oxidizes when the mold is opened, and this oxide forms in the cavity. This tends to cause casting defects.

Moreover, the pressure applied to the molten metal is increased or decreased by a servo valve, and pressure is constantly applied to the molten metal under the action of this servo valve. Therefore, when the mold is opened, there is a risk that the molten metal will overflow due to malfunction of the servo valve.

The present invention solves this kind of problem, and is a low-pressure casting method that does not disturb the molten metal in the furnace and can prevent the generation of oxides in the molten metal as much as possible. The purpose is to provide a method.

A further object of the present invention is to provide a low-pressure casting apparatus that can effectively pressurize and depressurize the molten metal and prevent the molten metal from leaking out unnecessarily.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a process of applying pressure on the surface of the molten metal in the furnace and filling and pressurizing the molten metal into the cavity in the mold via the stalk. , a step of reducing the pressure on the surface of the molten metal; a step of opening the mold and removing the cast product while the pressure on the surface of the molten metal is at least greater than atmospheric pressure; and after opening the mold. , a step of reducing the pressure on the surface of the molten metal to atmospheric pressure;

Furthermore, the present invention provides a servo valve for applying fluid pressure on the surface of the molten metal in order to fill and pressurize the cavity in the mold with the molten metal in the furnace via the stalk; a first discharge valve for reducing the pressure; and a second discharge valve that can be activated at the same time as the first discharge valve in order to further rapidly reduce the fluid pressure on the molten metal surface, and at least The first discharge valve and the second discharge valve are connected in parallel.

[Function] In the low-pressure casting method according to the present invention described above, the molten metal in the furnace is
After the cavity is filled and pressurized, the mold is opened while the pressure on the surface of the molten metal is reduced to at least a pressure greater than atmospheric pressure. Therefore, the molten metal in the stalk can be prevented from falling when the mold is opened. and,
After opening the mold, the pressure on the surface of the molten metal is reduced to atmospheric pressure and the molten metal in the stalk is returned to the furnace, making it possible to prevent the generation of oxides.

Further, in the low-pressure casting apparatus according to the present invention, after the molten metal in the furnace is filled into the cavity and pressurized via the servo valve, the first and second discharge valves are selectively energized to release the molten metal. The fluid pressure on the surface is reduced. Therefore, even if the servo valve malfunctions, the molten metal can be reliably depressurized.
It becomes possible to prevent this molten metal from leaking out as much as possible.

[Embodiments] The low-pressure casting method according to the present invention will be described in detail below with reference to the accompanying drawings by way of embodiments in connection with an apparatus for carrying out the method.

In FIG. 1, reference numeral 10 indicates a low pressure casting apparatus according to this embodiment. This low-pressure casting apparatus 10 includes a furnace 14 that holds a molten metal 12, a mold 18 that can be opened and closed to form a cavity 16 for a cast product, a stalk 20 that communicates the furnace 14 and the cavity 16, and a molten metal 12 in the furnace 14. In order to fill and pressurize the cavity 16 through the stalk 20 and the gate 21, a servo valve 22 for applying fluid pressure on the surface of the molten metal 12, and a first servo valve 22 for reducing the fluid pressure to the molten metal 12 are provided. A discharge valve 24 and a second discharge valve 26 that can be activated simultaneously with the first discharge valve 24 are provided in order to more rapidly reduce the fluid pressure to the molten metal 12.

The servo valve 22 is connected to an air supply source 30, and between the servo valve 22 and the air supply source 30, a filter 32, an oil mist separator 34, and a pressure reducing valve 36 are provided.
will be placed. The outlet side of the servo valve 22 communicates with the inside of the furnace 14 via a conduit 38a.

The first discharge valve 24 is a two-point/two-position switching valve, and communicates with the conduit 38b via the throttle valve 40.

The second discharge valve 26 includes an on-off valve 44 that is substantially connected to the cylinder 42, and the first discharge valve 26 is connected to the pipe line 38b.
4 in parallel.

Note that, in place of the second discharge valve 26, a two-point/two-position switching valve may be used similarly to the first discharge valve 24.

The control circuit of the low-pressure casting apparatus 10 includes a microprocessor 50 including a CPU, and this microprocessor 50 supplies a driving signal to the servo valve 22 via an interface 52 and an amplifier 54, while controlling the flow of the molten metal 12 in the furnace 14. Pressure is input as a signal via a pressure sensor 56 and an amplifier 58.

The first discharge valve 24 and the second discharge valve 26 are driven and controlled by a control circuit separate from the microprocessor 50.

Next, the operation of the low-pressure casting apparatus configured as described above will be explained below in relation to the low-pressure casting method according to this embodiment.

The mold 18 is clamped, and a cavity 16 is formed within this mold 18.
After this is formed, the servo valve 22 is driven by the output signal from the microprocessor 50, and the air supply source 30 and the conduit 38a are brought into communication. Therefore, compressed air flows through the filter 32, oil mist separator 34, and pressure reducing valve 36.
The molten metal 12 is introduced onto the surface of the molten metal 12 in the furnace 14 through the molten metal.

When the pressure applied to the molten metal 12 reaches pressure P1 as shown in FIG. 2 (time Tl), the molten metal 12 in the furnace 14 rises to the gate 21 via the stalk 20.

The pressure applied to the molten metal 12 is further increased to a pressure P
At time T2>, the microprocessor 50 supplies an output signal to the servo valve 22 according to the human power signal from the pressure sensor 56, so that the servo valve 22 is maintained in a constant throttle state. As a result, the molten metal 12 is filled into the cavity 16 and pressurized.

By holding the pressure P2 for a predetermined time, the molten metal 12 in the cavity 16 solidifies, and then from time T3, the first discharge valve 24 is opened via a control circuit (not shown), and the pressure in the furnace 14 is reduced. Air is gradually drawn off via the throttle valve 40 and this first exhaust valve 24 .

When the pressure inside the furnace 14 reaches a pressure P3 that is slightly lower than the pressure P1 and at least higher than atmospheric pressure, the first discharge valve 24 is closed and the pressure applied to the molten metal 12 is reduced. - It will be stopped once.

In this state, the mold 18 is opened and the cast product is taken out (time T4). Here, since the pressure inside the furnace 14 is maintained at P3, the molten metal 12 inside the stalk 20 does not fall into the furnace 14 when the mold is opened. Therefore, melt! 1
This has the effect of preventing the disturbance of No. 2.

Moreover, since the pressure P3 is maintained smaller than the pressure P2, the upper surface of the molten metal 12 in the stalk 20 is
The molten metal 12 is cooled and the molten metal 12 can be prevented from leaking out from the stalk 20.

After the work for taking out the cast product is completed, the pressure inside the furnace 14 is gradually reduced to atmospheric pressure under the action of the first discharge valve 24 (from time T5 to time T6). Therefore, the molten metal 12 does not remain in the stalk 20, and the generation of oxides can be prevented as much as possible. Moreover, since the compressed air is gradually led out to the atmosphere by the throttle valve 40, even if the distance between the molten metal 12 in the stoke 20 and the molten metal 12 in the furnace 14 is relatively large, the molten metal in the stoke 20 12 is
The molten metal 12 is prevented from falling rapidly, and disturbance of the molten metal 12 can be more effectively prevented.

Furthermore, since the first discharge valve 24 and the second discharge valve 26 are connected in parallel, after the casting work is finished,
Until the pressure inside the furnace 14 is reduced to atmospheric pressure,
This second discharge valve 26 can be energized. In other words, the valve 244 is opened and the compressed air is led out from the on-off valve 44 as well. This makes it possible to efficiently and reliably reduce the pressure inside the furnace 14 to atmospheric pressure.

In this example, the mold opening operation is performed while the pressure is once reduced to P3, but as shown in FIG. The mold can also be opened during the process.

[Effects of the Invention] As described above, the low pressure casting method according to the present invention has the following effects and advantages.

The mold is opened in order to remove the casting while the molten metal in the furnace is maintained at a pressure higher than atmospheric pressure, which prevents the molten metal in the stalk from falling into the furnace. .

Moreover, since the pressure on the surface of the molten metal is reduced to atmospheric pressure after the mold is opened, the molten metal in the stalk is returned to the furnace, and oxides are prevented from being generated in the molten metal as much as possible. It becomes possible.

Furthermore, in the low-pressure casting apparatus according to the present invention, the molten metal in the furnace is pressurized via the servo valve, while being depressurized via the first and second discharge valves.

Therefore, even if the servo valve malfunctions, the pressure of the molten metal can be reliably reduced, and leakage of the molten metal can be prevented as much as possible.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for implementing the low-pressure casting method according to the present invention, and FIGS. 2 and 3 are diagrams showing the relationship between time and pressure in the low-pressure casting method. 10...Low pressure casting device 12...Molten metal 14...Furnace 16...Cavity 18...Mold 20...Stoke 22...Servo valve 24.26-...Discharge valve 50...・Microprocessor (1 other person) FIG, 2 FIG, 3

Claims (3)

[Claims] (1) A process of applying pressure on the surface of the molten metal in the furnace and filling and pressurizing the molten metal into a cavity in the mold via a stalk, a process of reducing the pressure on the surface of the molten metal, and a process of reducing the pressure on the surface of the molten metal. has the following steps: opening the mold and removing the cast product in a state that is at least higher than atmospheric pressure; and reducing the pressure on the surface of the molten metal to atmospheric pressure after opening the mold. Characteristic low pressure casting method. (2) The method according to claim 1, further comprising: reducing the pressure on the molten metal surface at a first pressure reduction rate after opening the mold; and reducing the pressure on the molten metal surface at a second pressure reduction rate faster than the first pressure reduction rate.
A low-pressure casting method characterized by comprising: a step of reducing the pressure to atmospheric pressure at a reduced pressure rate; (3) A servo valve for applying fluid pressure on the molten metal surface in order to fill and pressurize the molten metal in the furnace into the cavity in the mold via the stalk; and for reducing the fluid pressure on the molten metal surface. a first discharge valve; and a second discharge valve that can be activated at the same time as the first discharge valve in order to further rapidly reduce the fluid pressure on the surface of the molten metal, and at least the first discharge valve. A low-pressure casting device characterized in that a discharge valve and a second discharge valve are connected in parallel.