JPH04319062A - Low pressure casting apparatus - Google Patents

Abstract

PURPOSE:To obtain a low pressure casting apparatus, by which submerged depth of a stake into molten metal can be always kept to the constant without directly detecting height of upper surface of the molten metal in a crucible. CONSTITUTION:By supplying Ar gas into the crucible 14 holding the molten Mg 30, the molten metal 30 is poured into cavity 44 in a sand mold 42 through the stoke 48. Then, pressure in closed space 26 in the crucible 14 is detected with pressure sensor 108 and based on this detected value in a controller 74, the aimed height of a supporting table 12 for supporting the crucible 14 is calculated, and by ascending the supporting table 12 with a lifting device, the submerged depth h0 of stoke 48 into the molten metal 30 is kept to the constant. As a detecting device is not arranged in the closed space 26, the detecting error caused by stickness of the molten metal 30 is prevented and also service life of the apparatus is improved. Further, mixture of inclusion into the molten metal 30 is avoided.

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 apparatus, and more particularly to a low-pressure casting apparatus that performs casting while maintaining a constant depth of immersion of a stalk into molten metal in a crucible.

0002

2. Description of the Related Art One type of low-pressure casting apparatus is one that applies gas pressure to the upper surface of the molten metal to inject the molten metal into a mold cavity through a stalk whose one end is immersed in the molten metal. For example, the apparatus of Utility Model Application Publication No. 61-17271 consists of (1) a furnace body, (2) a crucible that is supported by the furnace body and holds the molten metal in a substantially airtight closed space, and (2) above the furnace body. (1) a mold having a cavity that is installed in the mold and communicates with the inside of the molten metal through a stalk; (1) a gas supply device that injects the molten metal into the cavity via the stalk by supplying pressurized gas to the closed space; (2) a gas supply device that raises and lowers the crucible; It is configured to include a lifting device that maintains a constant height between the upper surface of the molten metal in the crucible and the lower end of the stalk. After a predetermined amount of molten metal is filled into the crucible, pressurized gas is supplied from a gas supply device to the closed space, whereby the molten metal is pushed up through the stalk and injected into the cavity. Furthermore, the depth of immersion of the stalk into the molten metal is maintained approximately constant by the operation of the lifting device.

[0003] For this purpose, this apparatus is provided with a detection device for detecting the height of the upper surface of the molten metal. The detection device is
It has first and second detection rods of different lengths. The first detection rod is slightly longer than the second detection rod, and its lower end is slightly lower than the second detection rod. When the molten metal in the crucible that is injected into the cavity decreases and the top surface of the molten metal falls to expose the tip of the first detection rod, a detection signal is issued, and the lifting device is activated to raise the crucible. If the crucible rises and the tip of the first detection rod is immersed into the molten metal again, and the top surface of the molten metal rises to the tip of the second detection rod, a detection signal will be emitted from the second detection rod. The operation of the lifting device is stopped.

In this way, by directly detecting the height of the upper surface of the molten metal, it is possible to raise the crucible by an arbitrary distance in response to the decrease in the molten metal in the crucible, and the upper surface of the molten metal is always connected to the lower end of the stalk. The relative height, ie, the depth of immersion of the stalk into the molten metal, can be kept constant. If the relative height between the top of the molten metal and the bottom of the stalk is not kept constant,
As the amount of molten metal in the crucible decreases, the depth of immersion of the stalk into the molten metal becomes shallower, and the lower end of the stalk is exposed from the molten metal, potentially making pouring impossible. In addition, if the depth of immersion of the stalk into the molten metal is set deep in advance to prevent this, impurities that settle at the bottom of the crucible will be more likely to be injected into the cavity together with the molten metal, reducing the quality of the product. This causes an inconvenience. On the other hand, in the above device, the depth of immersion of the stalk into the molten metal can always be maintained at an appropriate level, and impurities at the bottom of the crucible are prevented from entering the cavity, and the lower end of the stalk is not exposed from the molten metal. Good avoidance.

[0005]

[Problem to be Solved by the Invention] However, since the above-mentioned detection device detects the height of the upper surface of the molten metal using a detection rod, the molten metal adheres to the detection rod and it becomes dirty, making it impossible to perform accurate measurements. There was a problem with it disappearing. Also,
Since the detection rod is provided above the molten metal, it is easily deteriorated by radiant heat and has the problem of short device life. Furthermore, there is a problem that impurities may be mixed into the molten metal due to the detection rod being immersed in the molten metal, which is not desirable.

In view of the above-mentioned problems, the present invention has been made with the object of providing a low-pressure casting device that can always keep the depth of immersion of the stalk into the molten metal constant without directly detecting the height of the top surface of the molten metal. It is what was done.

[0007]

[Means for Solving the Problems] The gist of the present invention is to: detect pressure in a closed space in a low-pressure casting apparatus including the furnace body, crucible, mold, gas supply device, and lifting device. (1) a calculation means for calculating the target height of either the crucible or the mold from the pressure detected by the pressure detection means; and (2) a calculation means for calculating the target height of either the crucible or the mold. The present invention is provided with a lifting device control means for controlling the lifting device so that the lifting device is located at a target height.

[0008]

[Operation] In the low-pressure casting apparatus configured as described above, the pressure in the closed space of the crucible is detected by the pressure detection device, and based on the detected pressure, the calculation means determines which of the crucible and the mold holding the stalk is to be adjusted. The target height of either one is calculated. The pressure inside the mold cavity is constant (
Since the pressure in the closed space is detected, it is possible to calculate the difference in height between the top surface of the molten metal in the stalk or cavity and the top surface of the molten metal in the crucible. In addition, since the horizontal cross-sectional area at each height position of the stalk, cavity, and crucible and the position of the top surface of the molten metal in the crucible before injection starts are known in advance, if the pressure in the closed space is detected, the molten metal in the crucible The height of the top surface can be calculated. Therefore, it is possible to calculate what height the crucible or mold should be in order to keep the relative height between the lower end of the stalk and the upper surface of the molten metal in the crucible constant. Then, the lifting device is controlled by the lifting device control means so that the crucible or mold is positioned at the calculated target height. Eventually, if pressurized gas is supplied from the gas supply device into the closed space and the molten metal is pushed up, the crucible is raised by the lifting device as the molten metal in the crucible decreases, and the upper surface of the molten metal in the crucible and the lower end of the stalk are raised. The relative height with respect to this will always be kept constant.

[0009]

Effects of the Invention Since the pressure detecting means can detect pressure at a position away from the molten metal, accurate measurement can be performed without detection errors caused by adhesion of the molten metal. Furthermore, the device does not deteriorate due to radiant heat of the molten metal, and the device has a longer service life compared to conventional devices that directly detect the height of the top surface of the molten metal. Furthermore, since there is no need to immerse a detection rod or the like into the molten metal, there is no fear that impurities will be mixed into the molten metal, and the accuracy of the product can be improved.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. In FIG. 1, 10 is a furnace body, which is placed on a flat plate-shaped support 12. A crucible 14 is disposed within the furnace body 10 and supported by the furnace body 10 . The opening of the crucible 14 is closed by a lid member 16, and a flange formed around the opening of the crucible 14 and a corresponding flange of the lid member 16 are clamped by a clamper 22, so that the inside of the crucible 14 is airtightly closed. A closed space 26 is formed. Molten Mg (magnesium) 30 is held within the closed space 26 . M
The molten metal (hereinafter simply referred to as molten metal) 30 is obtained by heating and melting an ingot placed in the crucible 14 by the burner 32 of the furnace body 10 and refining it to remove oxides. The oxide becomes sluggish 34 and settles to the bottom of the crucible 14.

A surface plate 38 is provided above the furnace body 10. A plurality of pairs of wheels (not shown) are attached to the surface plate 38, and a pair of rails 4 are driven by a drive device (not shown).
0 horizontally. A sand mold 42 is placed on the surface plate 38. The sand mold 42 consists of a plurality of mold members, and a cavity 44 is formed within the sand mold 42 by these mold members. Further, a through hole 46 is formed in the center of the surface plate 38, and the upper end of the stalk 48 is inserted through and fixed, so that the stalk 48 is inserted into the cavity 4.
It communicates with 4. The surface plate 38 is moved above the crucible 14 and stopped when the stalk 48 reaches a position where it can be inserted into the crucible 14. It is fixed by a clamper 50. Note that 52 is a weight for preventing the sand mold 42 from floating or moving.

The lid member 16 has an opening 5 concentric with the crucible 14.
4 is formed on the top surface of the lid member 16, and an opening 54 is formed on the top surface of the lid member 16.
A spring 56 and a cylindrical pressure cloth 58 are fixed concentrically. A packing 60 is fixed to the upper ends of the spring 56 and the pressure cloth 58. A through hole 62 is formed in the center of the packing 60, through which the stalk 48 is inserted into the crucible 14.

A port 66 is formed in the lid member 16 and is connected via a conduit 68 to a gas cylinder 70 filled with Ar (argon) gas. Further, an electromagnetic directional switching valve 72 is provided between the pipe line 68 and the gas cylinder 70. The electromagnetic directional switching valve 72 is connected to a controller 74, and the controller 74 allows the closed space 26 in the crucible 14 to be placed in a pressurized position where it communicates with the gas cylinder 70, a depressurized position where it communicates with the atmosphere, and a holding position where it is blocked from both. It can be switched to At the pressurizing position, Ar gas in the gas cylinder 70 is supplied to the closed space 26 via the pipe 68, pressurizing the inside of the closed space 26, the pressurized state is maintained at the holding position, and the pressurized state is maintained at the depressurizing position. is released, and the pressure inside the closed space 26 is reduced to atmospheric pressure. In this embodiment, the pipe line 68, the gas cylinder 70
, an electromagnetic directional switching valve 72, and the like constitute a gas supply device.

A driving screw 76 is provided on the lower surface of the support base 12.
One end is fixed so that it cannot rotate. The drive screw 76 is
It is screwed into a nut 80 rotatably supported by the housing 78 via a bearing, and a large diameter gear 82 is provided integrally with the nut 80. The large diameter gear 82 is meshed with a small diameter gear 86 fixed to the rotating shaft of an electric motor 84. The electric motor 84 is connected to the controller 74 via a drive circuit 88.
The electric motor 84 is operated by the drive circuit 88 based on the output signal from the drive circuit 88, thereby rotating the nut 80 and moving the drive screw 76 in the axial direction.
2 and the furnace body 10, the crucible 14 is raised and lowered by an arbitrary amount.

In this embodiment, the sand mold 42 is installed so that it cannot move up and down, and the crucible 14 is moved up and down.
The electric motor 84, gears 82, 86, nut 80, drive screw 76, etc. constitute a lifting device that lifts and lowers the crucible 14,
The drive circuit 88 and part of the controller 74 constitute a lifting device control means.

Furthermore, a plurality of guide rods 90 are fixed to the lower surface of the support base 12. Each guide rod 90
is fitted into the sleeve 92 so as to be able to move in the axial direction, and moves in the axial direction together with the drive screw 76 to guide the raising and lowering of the support base 12.

A detection rod 96 is further attached to the lower surface of the support base 12. The detection rod 96 is inserted into a height detection device 98 fixed to a stand (not shown) so as to be movable in the axial direction.The insertion position of the detection rod 96 is detected within the height detection device 98, and the detection signal is output. The actual height of the support base 12 from the floor surface 100 is detected by inputting it to the controller 74 .

Another port 104 is formed in the lid member 16 and is connected via a pipe 106 to a pressure sensor 108 serving as pressure detection means. The pressure sensor 108 is connected to the controller 74 , and the detected value of the pressure within the closed space 26 of the crucible 14 is input to the controller 74 .

Within the controller 74, the pressure sensor 10
The target height of the crucible is calculated from the pressure inside the crucible 14 detected by 8. In this embodiment, a part of the controller 74 functions as a calculating means.

Next, the operation will be explained. First, with the support table 12 lowered to the lower end position, a prescribed amount of molten metal 30 is refined in the crucible 14 while air is removed by supplying Ar gas. Next, the surface plate 38 is moved to position the sand mold 42 above the crucible 14, and the surface plate 38 is fixed by the clamper 50 with the stalk 48 positioned above the through hole 62 of the packing 60. Subsequently, the support platform 12 is raised by the lifting device, and the height detection device 9
8, if it is detected that the support base 12 has actually risen by the initial rise amount H and reached the reference height, the lifting device is stopped. As the support stand 12 rises, the stalk 48 is inserted through the through hole 62 of the packing 60, and its lower end is exposed to the molten metal 3.
0 to a depth h0. The immersion depth h0 of the stalk 48 into the molten metal 30, that is, the height from the lower end surface of the stalk 48 to the upper surface of the molten metal 30 is approximately 50 to 100 mm.
It is desirable to set it as mm.

Further, as the support base 12 rises, the upper surface of the packing 60 comes into close contact with the lower surface of the surface plate 38, and the spring 56
When the packing 60 is pressed against the surface plate 38 by the urging force, a closed space 26 is formed in the crucible 14. After the closed space 26 is formed, the supply of Ar gas is stopped.

With the above preparations completed, the electromagnetic directional switching valve 72 is switched to the pressurizing position during pouring, and pressurizing Ar gas is supplied from the gas cylinder 70 into the closed space 26. As the pressure within the closed space 26 increases, the molten metal 30 is injected into the cavity 44 via the stalk 48. During this time, the pressure within the closed space 26 is detected by the pressure sensor 108, and the detected value is sent to the controller 74.

Within the controller 74, the pressure sensor 10
The target height of the support base 12 that supports the crucible 14 is calculated from the pressure detected by the pressure 8. First, closed space 2
6, the height from the upper surface of the molten metal 30 in the crucible 14 to the upper surface of the molten metal 30 rising toward the cavity 44 is calculated. If it is estimated from the calculated value that the upper surface of the molten metal 30 that has risen is still located within the stalk 48, the product of the calculated value and the cross-sectional area of the stalk 48 that has been input in advance, that is, the molten metal located within the stalk 48. 30 volumes are calculated. Further, when it is estimated that the molten metal 30 that has risen is located in the cavity 44 via the stalk 48, the cross-sectional area of the stalk 48 and the cross-sectional area of each part of the cavity 44 inputted in advance are used to move the molten metal 30 to the stalk 48 and the cavity 44. The volume of the injected molten metal 30 is calculated. The value obtained by dividing the calculated volume by the cross-sectional area S of the crucible 14 is the descending amount Δh of the upper surface of the molten metal 30 in the crucible 14, and the target height Δh' (=Δh
). In other words, the support stand 12 is moved from the reference height by Δh'.
When raised, the immersion depth h of the stalk 48 into the molten metal 30
0 is maintained at the same amount as before the start of pressurization.

The calculation of the target height Δh' is repeated at minute intervals, and the lifting device raises the support base 12 so that the height detected by the height detection device 98 matches the target height Δh'. .

[0025] When the cavity 44 is filled with the molten metal 30, the pressure increase gradient in the closed space 26 suddenly increases. In response, the electromagnetic directional switching valve 72 is switched to the holding state, and the injection of the molten metal 30 is completed. Then, a certain period of time during which the molten metal 30 in the cavity 44 is almost in a solidified state is measured, or
Alternatively, the molten metal 30 in the cavity 44 may be
When it is estimated that Ar is in a solidified state, the electromagnetic directional control valve 72 is switched to a reduced pressure state, and the Ar in the closed space 26 is
The gas is released to the atmosphere and the closed space 26 is depressurized to atmospheric pressure. At this time, the molten metal 30 accumulated in the stalk 48
The molten metal 3 flows backward and is returned to the crucible 14, but this molten metal 3
The amount Δh0 of 0 is input into the controller 74 in advance, and the support stand 12 is adjusted to Δh0 ′ (=Δ
h0) is lowered.

After the molten metal 30 in the cavity 44 is completely solidified, the support base 12 is lowered to the lower end position, and the stalk 48 is extracted from the crucible 14. Thereafter, the surface plate 38 is moved to the next process by the moving device, and the product is removed from the sand mold 42 and the like. Since a thin film of oxidized Mg is attached to the inner surface of the used stalk 48, it can be replaced with a new stalk 48. Next surface plate 38
When the sand mold 42 placed thereon is moved onto the crucible 14, the support base 12 is raised again and a second casting is performed. The initial rise amount of the support platform 12 at this time is H+Δ
It is assumed that h'-Δh0'.

[0027] If the amount of molten metal 30 in the crucible 14 decreases while casting is performed a plurality of times in the same manner, and the distance between the lathe 34 and the lower end of the stalk 48 becomes shorter than 150 to 200 mm, , as the molten metal 30 is poured, the slowness 34
Since there is a risk that molten metal may get mixed into the cavity 44, casting is performed again after adding new molten metal 30 to increase the amount of molten metal in the crucible 14 to a specified amount.

As is clear from the above description, in the present embodiment, the crucible 14 can be moved up and down with respect to the sand mold 42 via the furnace body 10 and the support stand 12, but the crucible cannot be moved up and down in a fixed manner. The mold holding the stalk may be raised and lowered relative to the crucible. In this case, a calculation means for calculating the target height of the mold and a lifting device control means for raising and lowering the mold to the calculated target height are provided.

Furthermore, in the present embodiment, the crucible 14, on which the target height of the support stand 12 is calculated, is moved up and down together with the support stand 12, but the target height of the crucible 14 itself is calculated, It is also possible to raise and lower only the crucible 14 using a lifting device.

Furthermore, in this embodiment, the crucible 14
A lid member 16 is attached to the crucible 14 to form a closed space 26 and pressurized gas is supplied to the crucible 14. However, pressurized gas may be supplied here.

[0031] In this embodiment, low-pressure casting of molten Mg 30 has been described, but low-pressure casting of molten Al (aluminum) can also be performed. In addition, although Ar gas was used as the pressurized gas in this example, other inert gases or 98% CO2 (carbon dioxide)
A gas containing 2% SF6 (sulfur hexafluoride) can be used.

In addition, the present invention can be practiced with various modifications and improvements based on the knowledge of those skilled in the art, such as using a hydraulic cylinder instead of the electric motor 84 as the drive source for the lifting device. .

[Brief explanation of drawings]

FIG. 1 is a front cross-sectional view showing essential parts of a low-pressure casting apparatus that is an embodiment of the present invention.

[Explanation of symbols]

10 Furnace body 12 Support stand 14 Crucible 26 Closed space 30 Mg (magnesium) molten metal 42 Sand mold 44 Cavity 48 Stoke 70 Gas cylinder 72 Solenoid directional valve 74 Controller 76 Drive screw 80 Nut 84 Electric motor 88 Drive circuit 108 Pressure sensor

Claims (1)

[Claims] Claims: 1. A furnace body, a crucible supported by the furnace body and holding the molten metal in a substantially airtight closed space, and a crucible provided above the furnace body and configured to hold the inside of the molten metal by means of a stalk. a mold having a cavity that communicates with the mold; a gas supply device that injects molten metal into the cavity via the stalk by supplying pressurized gas to the closed space;
Detecting the pressure in the closed space in a low-pressure casting device that includes a lifting device that lifts or lowers either the crucible or the mold to maintain a constant relative height between the upper surface of the molten metal in the crucible and the lower end of the stalk. pressure detection means; a calculation means for calculating a target height of either the crucible or the mold from the pressure detected by the pressure detection means; and a lifting device control means for controlling the lifting device so that the lifting device is positioned at a desired target height.