Water leakage monitoring device for vacuum casting system

Abstract

To more accurately determine the presence or absence of water leakage in a cavity in a vacuum casting system in which a pressure reducing valve is controlled to open and close so that a vacuum tank communicates with the cavity only during a period from when molten metal starts to be injected into the cavity until the molten metal is filled in the cavity, after the vacuum tank has been depressurized by a vacuum pump for casting a cast product, the vacuum casting system including a metallic mold 2 that defines a cavity 2a into which molten metal Lm is injected to mold the cast product, a vacuum tank 7 that selectively communicates with the inside of the cavity through the pressure reducing valve 4, and a vacuum pump 8 that selectively reduces the pressure in the vacuum tank.SOLUTION: A water leakage monitoring device 50 detects the humidity of a vacuum tank during a period from when molten metal starts to be injected into a cavity until the molten metal is filled in the cavity, and determines that water leakage has occurred when the humidity exceeds a predetermined value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vacuum casting system using a vacuum die casting method or the like, and more particularly to an apparatus configured to easily monitor water leakage in a mold of a vacuum casting system.

Background Art

[0002] Regarding vacuum casting systems by vacuum casting methods such as the vacuum die casting method for casting metal (such as aluminum) moldings with complex shapes, various configurations have been proposed. For example, in Patent Document 1, as a method for measuring the humidity in a cavity (mold) with higher accuracy in a die casting process, at a measurement region on an exhaust flow path that communicates the cavity and vacuum generating means (vacuum pump, vacuum tank), the humidity, temperature, and pressure of the gas are measured, and based on the measurement waveforms of each measured value for each casting cycle, a configuration for calculating the ratio of water molecules in the gas that passed through the measurement region during the casting cycle has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As schematically shown in Fig. 1(A), generally, in a vacuum casting system 1 using a vacuum die-casting method or the like, before the molten metal is poured into the cavity 2a of the mold 2, the cavity 2a is depressurized to remove as much air as possible. Therefore, an exhaust pipe 3 is connected to the cavity 2a via a pressure reducing valve 4, and the exhaust pipe 3 is connected to a vacuum tank 7 that is depressurized by a vacuum pump 8 via a check valve 5 and a pressure reducing filter 6. During the casting process of the casting, first, the pressure reducing valve 4 is closed to cut off the connection between the vacuum tank 7 and the cavity 2a, and then the vacuum pump 8 is operated to depressurize the inside of the vacuum tank 7. On the other hand, in the mold 2, as schematically shown in Fig. 1(B), molten metal Lm (molten aluminum or the like) is poured from the molten metal inlet 2b of the mold 2 into the cylindrical space 2c communicating with the cavity 2a. Inside the cylindrical space 2c, the plunger 20 moves in the direction of pushing the molten metal Lm into the cavity 2a (the injection direction). When the plunger 20 seals the molten metal inlet 2b and the molten metal Lm is blocked from the molten metal inlet 2b, the pressure reducing valve 4 is opened, and thereby the air in the cavity 2a is removed to the vacuum tank 7. Then, as schematically shown in Fig. 1(C), when the plunger 20 further moves in the direction of pushing the molten metal Lm from the cylindrical space 2c into the cavity 2a and the molten metal Lm reaches above the cavity 2a, a sensor (not shown) is activated, the pressure reducing valve 4 is closed again, and the vacuum tank 7 is cut off from the cavity 2a. After that, the molten metal Lm solidifies and the casting is completed.

[0005] In the above-described vacuum casting system 1, the mold 2 that defines the cavity 2a is formed of a steel material such as SKD material, and a circuit 22 through which cooling water flows is provided inside the mold for cooling. In such a mold 2, as schematically depicted in FIG. 2(A), when cracks occur in the steel material of the wall portion that defines the cavity 2a, or when gaps are formed at the joints between the wall portions when combining a plurality of wall portions to define the cavity 2a, water leakage (Dw) occurs where cooling water leaks from these into the cavity 2a. Then, the water turns into water vapor Gw, and problems such as defective appearance of the product and defective casting nests on the machined surface may occur. Therefore, when performing casting with the vacuum casting system 1, it is preferable to timely monitor whether there is water leakage into the cavity 2a of the mold 2. Thus, conventionally, as schematically depicted in FIG. 2(B), with reference to the pressure waveform in the exhaust pipe 3 when the vacuum tank 7 is connected to the cavity 2a and the pressure in the exhaust pipe 3 after the decompression of the cavity 2a (after the check valve of the pressure reducing valve closes again), it has been determined that there is water leakage when the pressure in the exhaust pipe 3 exceeds a predetermined threshold value. However, actually, as shown in the figure, although the pressure in the exhaust pipe 3 tends to increase after the decompression of the cavity 2a when there is water leakage, due to various other factors (such as variations in airtightness within the cavity 2a), there are large variations (SC) in the pressure waveform in the exhaust pipe 3 both when water leakage does not occur (nr) and when it occurs (ab), making it difficult to accurately determine whether there is water leakage.

[0006] In view of the above circumstances, the main problem of the present invention is to provide a water leakage monitoring device that can more accurately determine whether there is water leakage in the cavity of the mold of a vacuum casting system.

[0007] Regarding this point, in the series of steps in the above-described vacuum casting system 1, after the vacuum tank 7 is depressurized by the vacuum pump 8, it is disconnected from the vacuum pump 8, and is connected to the cavity 2a only from the time when the molten metal Lm starts to be injected into the cavity 2a until the molten metal Lm reaches the upper part of the cavity 2a. And after the decompression of the cavity 2a is completed, air (and moisture of the mold release agent) in the cavity 2a accumulates in the vacuum tank 7. If water leakage occurs in the cavity 2a, the leaked water also accumulates as steam. Also, since the vacuum tank 7 is arranged at a place relatively far from the cavity 2a, it is in an environment where the temperature and pressure are relatively stable. On the other hand, in the cavity 2a, if there is no water leakage, except for the moisture of the mold release agent for releasing the casting, there is substantially no moisture. Therefore, if water leakage occurs, the humidity in the vacuum tank 7 after the decompression of the cavity 2a ends becomes significantly higher than when there is no water leakage. That is, it is possible to determine the water leakage in the cavity 2a in the above-described vacuum casting system 1 from the high humidity in the vacuum tank 7 after the decompression of the cavity 2a ends. This finding is utilized in the present invention.

Means for Solving the Problems

[0008] According to one aspect of the present invention, the above problem is solved by a mold that defines a cavity into which a molten metal is injected to form a casting, a vacuum tank that is selectively communicated with the cavity via a pressure reducing valve, and a vacuum pump that selectively depressurizes the inside of the vacuum tank. During the casting of the casting, after the vacuum tank is depressurized by the vacuum pump, the pressure reducing valve is opened and closed so that the vacuum tank is communicated with the cavity only from the time when the molten metal starts to be injected into the cavity until the cavity is filled with the molten metal. A water leakage monitoring device for monitoring the presence or absence of water leakage from a cooling water circuit flowing into the cavity in the mold in the vacuum casting system, humidity detection means for detecting the humidity in the vacuum tank, When the humidity of the vacuum tank after the molten metal starts to be injected into the cavity and before the cavity is filled with the molten metal exceeds a predetermined value, a water leakage determination means for determining that water leakage has occurred from the cooling water circuit flowing in the mold into the cavity is achieved by a water leakage monitoring device having the same.

[0009] In the above configuration, the "vacuum casting system" may be a system using a vacuum die-casting method or the like that manufactures a cast product by injecting molten metal into a cavity of a mold while reducing the pressure in the cavity in the manner described above. The mold is formed of a material commonly used in this field, such as SKD steel, and a cooling circuit through which cooling water flows is disposed inside the wall portion thereof. The vacuum tank and the vacuum pump may be ordinary ones used in this field. The pressure reducing valve may be an on-off valve in a normal mode that selectively communicates the vacuum tank and the cavity of the mold. The "humidity detection means" may be any type of humidity sensor or hygrometer that detects the humidity in a gas in a normal mode. The "water leakage determination means" may be any type of determination device that determines that there is water leakage in the cavity of the mold when the humidity detected by the humidity detection means exceeds a predetermined value set as appropriate, and may be an independent system, but may be incorporated as a part of a control device that controls the operation of the vacuum casting system.

[0010] According to the above configuration, the presence or absence of water leakage in the cavity of the mold is not determined by the pressure change during decompression in the cavity of the mold or the pressure after decompression, but is determined by the humidity in the vacuum tank cut off from the cavity after decompression. After decompression, if there is water leakage in the cavity of the mold, it is assumed that a large amount of water vapor has accumulated in the vacuum tank. Therefore, it is expected that the presence or absence of water leakage can be determined more accurately.

[0011] The predetermined value for the humidity of the vacuum tank in the water leakage determination means may be set to the lowest value of the humidity assumed in the case of water leakage in consideration of the fact that moisture from the mold release agent also exists in the cavity.

Advantages of the Invention

[0012] Thus, according to the present invention, in the process flow of the casting process in the vacuum casting system, the evacuated vacuum tank is connected to the cavity of the mold only until the molten metal fills the cavity, and then it is separated from the cavity and the vacuum pump. Focusing on the fact that if there is moisture in the cavity, it should accumulate in the vacuum tank, the presence or absence of water leakage in the mold cavity is monitored by referring to the humidity of the vacuum tank after the decompression is completed. According to such a configuration, the humidity of the vacuum tank corresponds to the amount of water vapor flowing from the cavity into the vacuum tank and is not affected by factors such as the airtightness in the cavity. Therefore, it is expected that the presence or absence of water leakage can be determined more accurately than before. The configuration of the present invention may be applied to various vacuum casting systems.

[0013] Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Description of Reference Numerals

[0015] 1…Vacuum casting system, 2…Mold, 2a…Cavity (in the mold), 2b…Molten metal inlet, 2c…Cylindrical space, 3…Exhaust pipe, 4…Pressure reducing valve, 5…Check valve, 6…Vacuum filter, 7…Vacuum tank, 8…Vacuum pump, 8a…On-off valve, 9…Hygrometer, pressure gauge, 10…Internal cavity pressure gauge, 20…Plunger, 22…Cooling water circuit, 50…Control device (including leakage monitoring means), Lm…Molten metal, Dw…Leaked water, Gs…Water vapor

Best Mode for Carrying Out the Invention

[0016] Configuration of the system The leakage monitoring device according to this embodiment may be applied to a vacuum casting system 1 using a vacuum die casting method or the like as schematically depicted in Fig. 1(A). In the vacuum casting system 1, as already mentioned, an exhaust pipe 3 to which a vacuum tank 7 is connected via a pressure reducing valve 4 is connected to a cavity 2a defined inside a mold 2 formed of a steel material such as SKD material. The vacuum pump 8 is connected to the vacuum tank 7 via a valve 8a so as to be able to reduce the pressure. As depicted in Figs. 1(B) and (C), a cylindrical space 2c for receiving molten metal from an inlet 2b and a plunger 20 that moves to inject the molten metal from the cylindrical space 2c into the cavity 2a are provided at the lower part of the cavity 2a. Further, inside the wall portion of the mold 2, a cooling water circuit through which cooling water for cooling the mold flows is appropriately arranged. Furthermore, near the pressure reducing valve 4, an internal cavity pressure gauge for detecting the pressure inside the cavity 2a and a sensor for detecting that the molten metal has reached the upper part of the cavity are provided. And the state of each part of the system is monitored by a control device 50, and the control device 50 may be configured to control the operations of each part such as the operation of the vacuum pump 8, the opening and closing of valves 8 and the pressure reducing valve 4, and the movement of the plunger 20. The control device 50 may be a normal computer device that operates according to a program.

[0017] In the casting process by the above system, before the molten metal is injected into the cavity 2a which is the mold, first, with the pressure reducing valve 4 closed, the vacuum tank 7 is depressurized by the vacuum pump 8. When the depressurization is completed, the valve 8a is closed and the communication between the vacuum pump 8 and the vacuum tank 7 is cut off. On the other hand, in the mold 2, the molten metal Lm is poured into the cylinder-shaped space 2c communicating with the cavity 2a. The molten metal Lm may be a normal material used in this field, such as molten aluminum. After that, when the plunger 20 moves in the cylinder-shaped space 2c to seal the molten metal injection port 2b and starts to inject the molten metal Lm into the cavity 2a, the pressure reducing valve 4 is opened (at t0 in Fig. 2(B)). Thereby, the air in the cavity 2a is removed to the vacuum tank 7. And as schematically depicted in Fig. 1(C), when the plunger 20 further moves deeper into the cylinder-shaped space 2c, the molten metal Lm is injected into the cavity 2a, and when the molten metal Lm reaches above the cavity 2a, this is sensed by the sensor and the pressure reducing valve 4 is closed again (at t2 in Fig. 2(B)). While the vacuum tank 7 is cut off from the cavity 2a, the molten metal Lm is cooled and solidified, and thus the casting product is completed.

[0018] Detection of water leakage in the cavity of the mold As described in the "Summary of the Invention", in this embodiment, a hygrometer or humidity sensor for detecting humidity is installed in the vacuum tank 7, and as described above, the humidity in the vacuum tank 7 at the stage when the depressurization in the cavity 2a is completed (after t2 in Fig. 2(B)) is detected. If there is water leakage in the cavity 2a, the moisture is sucked into the vacuum tank 7 as water vapor and stays there, and the moisture content in the gas in the vacuum tank 7 becomes higher than that in the case of only the moisture of the mold release agent. Therefore, when the humidity in the vacuum tank 7 detected as described above is higher than a predetermined value (threshold value), it is possible to determine that there is water leakage in the cavity 2a. The threshold value for humidity may be determined experimentally or by calculation so as to be higher than the humidity when only the moisture of the mold release agent is taken into the vacuum tank as moisture. The determination of whether the humidity in the vacuum tank 7 has reached the threshold value may be achieved by the operation according to the program by the control device 50.

[0019] According to the configuration of the present embodiment, the presence or absence of water leakage in the cavity is determined by the humidity in the vacuum tank, rather than the pressure waveform or the absolute pressure of the decompression of the cavity with large variations. In principle, if there is no water leakage, the moisture in the vacuum tank is only the moisture of the mold release agent. Therefore, if the moisture content increases, it is considered to be due to water leakage into the cavity of the mold. Thus, it is expected that the presence or absence of water leakage into the cavity can be detected more accurately and with fewer false detections than before.

[0020] The above description has been made in relation to the embodiments of the present invention, but many modifications and changes are easily possible for those skilled in the art. It is obvious that the present invention is not limited to only the embodiments illustrated above, and can be applied to various devices without departing from the concept of the present invention.

Claims

Claim 1 A mold that defines a cavity into which a molten metal is poured to form a casting, a vacuum tank selectively communicating with the cavity via a pressure reducing valve, and a vacuum pump for selectively reducing the pressure in the vacuum tank. During the casting of the casting, after the vacuum tank is evacuated by the vacuum pump, the pressure reducing valve is opened and closed so that the vacuum tank communicates with the cavity only from the start of injection of the molten metal into the cavity until the cavity is filled with the molten metal. A water leakage monitoring device for monitoring the presence or absence of water leakage from a cooling water circuit flowing in the mold into the cavity in a vacuum casting system, humidity detecting means for detecting the humidity in the vacuum tank; water leakage determining means for determining that water leakage has occurred from the cooling water circuit flowing in the mold into the cavity when the humidity in the vacuum tank exceeds a predetermined value after the start of injection of the molten metal into the cavity until the cavity is filled with the molten metal; A water leakage monitoring device having the above.

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