Neutron modeling device and neutron modeling method

Abstract

To provide a device for molding a core allowing for reducing poor filling of sand.SOLUTION: A device for molding a core comprises a die body 20 internally formed with a hollow space 22 and a blow head 11 for supplying, by mixing together, foundry sand and gas into the hollow space 22. In the die body 20, a plurality of gas vents 36 are formed to serve as passages of gas flowing out of the hollow space 22. The flow of gas within the gas vents 36 can be regulated separately on each gas vent 36 basis.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a neutron molding apparatus and a neutron molding method.

Background Art

[0002] Japanese Patent Application Laid-Open No. 60-56441 (Patent Document 1) describes a configuration in which a cavity is formed inside a mold box, a hollow chamber is formed separately from the cavity, the cavity and the hollow chamber communicate with each other through a plurality of air passages, and the hollow chamber communicates with the outside of the mold box through one air passage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a neutron molding apparatus, depending on the shape of the hollow space formed in the mold body filled with casting sand, a sand clogging defect may occur where a part of the hollow space is not filled with casting sand.

[0005] The present disclosure proposes a neutron molding apparatus and a neutron molding method capable of reducing sand clogging defects.

Means for Solving the Problems

[0006] The neutron molding apparatus according to the present disclosure includes a mold body having a hollow space formed therein, and a casting sand supply device that mixes casting sand and gas and supplies the mixture to the hollow space. A plurality of air passages serving as passages for gas flowing out of the hollow space are formed in the mold body. The flow of gas in the air passages can be individually adjusted for each air passage.

[0007] In the core molding method according to the present disclosure, molding sand and gas are mixed and supplied into a hollow space formed inside a mold body. The mold body is formed with a first vent passage and a second vent passage that serve as passages for the gas flowing out from the hollow space. After starting ventilation to the first vent passage, the gas flow is adjusted so as to start ventilation to the second vent passage.

Effect of the Invention

[0008] According to the core molding apparatus and the core molding method according to the present disclosure, the defect of sand clogging can be reduced.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the specification and drawings, the same components or corresponding components are denoted by the same reference numerals, and redundant descriptions will not be repeated. Also, in the drawings, for the sake of convenience of explanation, the configuration may be omitted or simplified in some cases.

[0011] <First Embodiment> FIG. 1 is a diagram showing an outline of the configuration of a core molding apparatus 1 according to the first embodiment. A sand tank 4 stores raw sand. A mixer 5 is arranged below the sand tank 4. The mixer 5 kneads raw sand with additives, resin, etc. to produce molding sand. The molding sand is supplied to a blow head 11 via a hopper 6. The sand tank 4 and the mixer 5 are arranged above a scaffold 7. A fence 8 is provided at the edge of the scaffold 7. The blow head 11 is arranged below the scaffold 7. The hopper 6 is arranged so as to penetrate the scaffold 7 in the vertical direction.

[0012] The blow head 11 stores molding sand. A pressurized gas supply device (not shown) supplies pressurized gas into the blow head 11. Typically, the pressurized gas supply device compresses air and supplies it into the blow head 11. The blow head 11 mixes molding sand and gas.

[0013] A blow nozzle 12 (not shown in FIG. 1) is attached to a blow plate 13 and arranged to communicate with the inside of the blow head 11. The blow plate 13 has a flat plate shape and is arranged between the blow head 11 and the mold body 20. The blow head 11 and the blow nozzle 12 constitute the molding sand supply device of the embodiment. The molding sand supply device is controlled to be able to switch the supply and stop of molding sand to the mold body 20.

[0014] The mold body 20 is mounted on the mold base 41. A mold release workbench 42 is arranged on the side (right side in FIG. 1) of the mold base 41, and a hardening device 43 is further arranged on the side. The mold body 20 can reciprocate between the mold base 41, the mold release workbench 42, and the hardening device 43, for example, by a roller conveyor.

[0015] After the mold body 20 is filled with casting sand, a hardening gas such as carbon dioxide gas is blown into the mold body 20 from the gas port 44 of the hardening device 43 to harden the casting sand. At the mold release workbench 42, the mold body 20 is divided into a plurality of parts. The cores formed of the hardened casting sand are taken out from the mold body 20.

[0016] One end of each of a plurality of vent pipes 50 is connected to the mold body 20. The other end of each of the plurality of vent pipes 50 is connected to a solenoid valve unit 60. The solenoid valve unit 60 has a plurality of solenoid valves 61. Each of the plurality of vent pipes 50 is connected to any one of the plurality of solenoid valves 61. The number of vent pipes 50 and the number of solenoid valves 61 provided in the solenoid valve unit 60 do not necessarily have to be the same. The number of solenoid valves 61 may be more than the number of vent pipes 50. Depending on the number of vent pipes 50, one or more solenoid valves 61 may not be connected to the vent pipes 50.

[0017] The solenoid valve unit 60 is connected to an exhaust fan 71. A decompression chamber 72 is arranged between the solenoid valve unit 60 and the exhaust fan 71.

[0018] FIG. 2 is a partial cross-sectional view showing the internal structure of the mold body 20 of the first embodiment. The mold body 20 is, for example, a wooden mold. A hollow space 22 is formed inside the mold body 20. Molding sand is supplied into the hollow space 22 from a molding sand supply device via an inlet 21 whose upper end of the hollow space 22 opens upward. The inlet 21 constitutes an inlet of the molding sand into the hollow space 22. The core molding device 1 supplies pressurized gas into the blow head 11, and blows the molding sand into the hollow space 22 of the mold body 20 through the blow nozzle 12 to fill the hollow space 22 with the molding sand.

[0019] As schematically shown in FIG. 2, with the blow plate 13 placed on the upper surface of the mold body 20, the blow nozzle 12 communicates with the inlet 21. The blow nozzle 12 is arranged to open toward the hollow space 22. From the blow head 11, the molding sand and the pressurized gas are supplied into the hollow space 22 in the mold body 20 through the blow nozzle 12. The molding sand is blown into the hollow space 22. The hollow space 22 is filled with the molding sand. The plurality of curved arrows shown in FIG. 2 schematically indicate the trajectories of the molding sand moving in the hollow space 22.

[0020] The hollow space 22 of the embodiment shown in FIG. 2 has a complex shape. When trying to fill the hollow space 22 with molding sand in a random manner, there are concern areas where the molding sand is likely to become clogged and sand clogging defects may occur. The concern areas are, for example, the tip portions 24 (24A, 24B) at the tip of the hollow space 22, the upper recess 25 where the upper surface of the hollow space 22 is recessed upward, the confluence portion 26 where the molding sand flowing in the hollow space 22 during the molding process swirls and merges, and the like.

[0021] Since the tip portion 24A is located at the tip position of the hollow space 22 with a small cross-sectional area and a long path, if the exhaust from the vent 30A1 is insufficient, an air pocket may form at the tip portion 24, and even if pressure is applied, the casting sand may not clog up to the tip portion 24. Similarly, an air pocket may form at the confluence portion 26, reducing the fluidity of the casting sand and potentially causing the casting sand to clog at the confluence portion 26. In the upper recess 25, since the casting sand is to be filled against gravity, if the casting sand cannot flow upward against gravity, the casting sand may not clog in the upper recess 25.

[0022] In addition to being away from the blow nozzle 12, the tip portion 24B is also away from the bent portion 28 where the flow direction of the casting sand suddenly changes. There is a possibility that the casting sand cannot reach the tip portion 24B and the tip portion 24B may become clogged with casting sand. At the bent portion 28, the fluidity of the casting sand decreases and the casting sand stagnates, blocking the upstream portion 29 upstream of the bent portion 28 in the moving direction of the casting sand in the hollow space 22, preventing the casting sand from being efficiently fed to the tip portion 24B and raising concerns about sand clogging defects.

[0023] The mold body 20 is formed with a plurality of ventilation passages 36 that communicate the hollow space 22 with the outer surface of the mold body 20. The ventilation passages 36 serve as passages for the gas flowing out of the hollow space 22. A vent 30 is provided at the gas extraction port from the hollow space 22 to the ventilation passages 36. The vent 30 is provided for the purpose of discharging the pressurized gas blown into the hollow space 22 together with the casting sand from the hollow space 22 to the outside. The vent 30 has, for example, a shape with a plurality of narrow slits formed or a fine mesh shape. The vent 30 allows the flow of the gas passing through the vent 30. The vent 30 is formed so that the casting sand cannot pass through the vent 30.

[0024] Specifically, a vent 30A1 is disposed on the end face of the hollow space 22 facing the tip portion 24A. The ventilation passage 36A1 communicates the vent 30A1 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30A1. A vent 30A2 is disposed on the upper surface of the hollow space 22 closer to the inlet 21 than the vent 30A1. The ventilation passage 36A2 communicates the vent 30A2 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30A2. A vent 30A3 is disposed on the upper surface of the hollow space 22 closer to the inlet 21 than the vent 30A2. The ventilation passage 36A3 communicates the vent 30A3 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30A3.

[0025] A vent 30B2 is disposed on the upper surface of the hollow space 22 facing the upper recess 25. The ventilation passage 36B2 communicates the vent 30B2 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30B2. A vent 30B1 is disposed on the end face of the hollow space 22 facing the tip portion 24B, farther from the inlet 21 than the vent 30B2. The ventilation passage 36B1 communicates the vent 30B1 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30B1.

[0026] A vent 30B3 is disposed on the upper surface of the hollow space 22 closer to the inlet 21 than the vent 30B2. The ventilation passage 36B3 communicates the vent 30B3 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30B3. A vent 30B4 is disposed on the upper surface of the hollow space 22 closer to the inlet 21 than the vent 30B3. The ventilation passage 36B4 communicates the vent 30B4 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30B4.

[0027] A vent 30C2 is disposed on a side surface of the hollow space 22 facing the confluence portion 26. The ventilation passage 36C2 communicates the vent 30C2 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30C2. A vent 30C1 is disposed on a side surface of the hollow space 22 below the vent 30C2. The ventilation passage 36C1 communicates the vent 30C1 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30C1. A vent 30C3 is disposed on the upper surface of the hollow space 22 closer to the inlet 21 than the vent 30C2. The ventilation passage 36C3 communicates the vent 30C3 with the outer surface of the mold body 20 and serves as a passage for the gas flowing out from the hollow space 22 through the vent 30C3.

[0028] FIG. 3 is a partial cross-sectional view showing an enlarged connection portion between the ventilation passage 36 and the ventilation pipe 50. As shown in FIG. 3, the ventilation passage 36 is exposed on the outer surface of the mold body 20. The ventilation pipe 50 is connected to an opening 38 where the ventilation passage 36 opens to the outer surface of the mold body 20. The ventilation pipe 50 has a coupler (not shown) at one end, and the ventilation pipe 50 may be connected to the ventilation passage 36 by inserting the coupler into the ventilation passage 36 from the opening 38. The opening 38 serves as an outlet for the gas from the ventilation passage 36. The gas flowing out from the ventilation passage 36 flows into the ventilation pipe 50 and flows through the ventilation pipe 50.

[0029] The ventilation pipe 50 is provided with a pressure sensor 52. The pressure sensor 52 can detect the pressure inside the ventilation pipe 50. The pressure sensor 52 is disposed outside the mold body 20. In order to detect the pressure inside the ventilation pipe 50 at a position closer to the connection portion with the ventilation passage 36, it is desirable that the pressure sensor 52 be disposed in the vicinity of the outer surface of the mold body 20.

[0030] FIG. 3 illustratively shows one of the plurality of ventilation passages 36 formed in the mold body 20. The structure shown in FIG. 3 is applicable to any of the ventilation passages 36A1 to 36A3, 36B1 to 36B4, and 36C1 to 36C3 shown in FIG. 2. The same number of ventilation pipes 50 as the ventilation passages 36 are provided. Each of the ventilation pipes 50 is individually connected to any one of the plurality of ventilation passages 36. The pressure sensor 52 is provided in each of the ventilation pipes 50. The pressure sensor 52 can detect the pressure value and the change in the pressure value (pressure change) within each ventilation passage 36.

[0031] As also shown in FIG. 1, the other end of the ventilation pipe 50 is connected to the solenoid valve unit 60. Although a simplified solenoid valve unit 60 is shown in FIG. 1, the solenoid valve unit 60 has more solenoid valves 61 than the number of ventilation passages 36 (and ventilation pipes 50). The ventilation pipe 50 individually connects any one of the plurality of ventilation passages 36 and any one of the plurality of solenoid valves 61.

[0032] The solenoid valves 61 are provided corresponding to each of the ventilation pipes 50. The solenoid valves 61 can open and close each of the ventilation pipes 50. By opening the solenoid valve 61, a gas flow is generated from the hollow space 22 of the mold body 20 through the corresponding vent 30, ventilation passage 36, and ventilation pipe 50. By closing the solenoid valve 61, the gas stops flowing through the corresponding vent 30, ventilation passage 36, and ventilation pipe 50. The solenoid valve 61 constitutes a flow rate adjustment valve of the embodiment that adjusts the flow rate of the gas flowing through each ventilation passage 36. By individually opening and closing the plurality of solenoid valves 61, the gas flow within the ventilation passage 36 can be individually adjusted for each ventilation passage 36. The flow rate adjustment valve is not limited to the solenoid valve 61 and may be an electric valve.

[0033] The exhaust fan 71 communicates with the ventilation passage 36 via the solenoid valve unit 60 and the ventilation pipe 50. The exhaust fan 71 corresponds to the suction device of the embodiment that sucks the gas in the ventilation passage 36. The ventilation passage 36 inside the mold body 20 and the ventilation pipe 50 outside the mold body 20 constitute a suction path through which the gas sucked by the suction device flows. The core molding apparatus 1 includes a plurality of suction paths, and each suction path corresponds to any one of the plurality of vents 30.

[0034] In the configuration shown in FIG. 1, a plurality of solenoid valves 61 are attached to one header pipe, and the header pipe is connected to the exhaust fan 71 via the decompression chamber 72. The present invention is not limited to this configuration. For example, each ventilation pipe 50 may be connected to a separate exhaust fan 71. In this case, even without a flow rate adjustment valve, by switching the start and stop of each exhaust fan 71, the flow of the gas in the ventilation passage 36 can be individually adjusted for each ventilation passage 36.

[0035] The portions where defects are concerned are not limited to the tip portions 24(24A, 24B), the upper concave portion 25, and the confluence portion 26 shown in FIG. 2. FIG. 4 is a cross-sectional view showing another example of the portion where defects are concerned. In FIG. 4, a constricted portion 27 is shown. The constricted portion 27 is a portion where the hollow space 22 is partially formed narrowly. When the molding sand passes through the constricted portion 27, the flow velocity of the molding sand decreases due to the friction between the wall surface of the constricted portion 27 and the molding sand. As a result, it becomes difficult for the molding sand to flow to the tip side of the hollow space 22 rather than the constricted portion 27, and the molding sand may be clogged at the tip. Since the constricted portion 27 shown in FIG. 4 extends in the lateral direction (horizontal direction), an upper concave portion 25 is formed on the tip side of the hollow space 22 rather than the constricted portion 27. Since the flow velocity of the molding sand is decreasing in the constricted portion 27, it becomes difficult for the molding sand to flow into the upper concave portion 25 against gravity, and the molding sand may be clogged in the upper concave portion 25.

[0036] FIG. 5 is a cross-sectional view showing still another example of a portion where there is a concern about defects. FIG. 5 shows a plurality of bent portions 28. In the bent portion 28, since the flow direction of the molding sand suddenly changes, collisions of the molding sand against the inner wall of the hollow space 22, friction between the inner wall of the hollow space 22 and the molding sand, and collisions and friction between the molding sands occur. In the bent portion 28, it becomes generally difficult for the molding sand to flow. As a result of the molding sand passing through the plurality of bent portions 28, it becomes difficult for the molding sand to flow toward the tip side of the hollow space 22 than the bent portion 28, and the tip portion 24 may be clogged with the molding sand.

[0037] In the core molding apparatus 1 of the embodiment, considering portions where there is a concern about defects such as the tip portions 24 (24A, 24B), the upper concave portion 25, the confluence portion 26, the narrow portion 27, and the bent portion 28, it is set which of the plurality of ventilation paths 36 the gas is preferentially flowed through. Thereby, even if there is a portion where there is a concern about defects where the sand is less likely to be clogged in the hollow space 22, by actively guiding the sand to the portion where there is a concern about defects, it becomes possible to appropriately fill the entire hollow space 22 with the molding sand, and the defect of sand clogging is reduced. FIG. 6 is a flowchart showing the flow of the process of the core molding method of the first embodiment.

[0038] As shown in FIG. 6, first, the sand is kneaded (step S1), and the sand tank 4 is filled with sand (step S2). The blow head 11 is filled with sand, and the blow plate 13 and the blow nozzle 12 above the mold body 20 are brought into close contact with each other. Further, a pressurized gas is supplied to the blow head 11 to apply a blow pressure (step S3).

[0039] Subsequently, the vent 30 near the portion where there is a concern about defects is opened. The other vents 30 are closed. That is, among the plurality of solenoid valves 61, the solenoid valve 61 communicating with the vent 30 that is the target to be opened via the ventilation path 36 and the ventilation pipe 50 is opened. By opening the solenoid valve 61, the gas can flow through the vent 30, the ventilation path 36, and the ventilation pipe 50 in order. In this state, the exhaust fan 71 is driven to suck the air in the ventilation pipe 50 and the ventilation path 36 (step S4).

[0040] Specifically, among the vents 30A1 to 30A3 shown in FIG. 2, vents 30A1 and 30A2 are opened in step S4. Vent 30A3 is closed. Among the vents 30B1 to 30B4, vents 30B1 and 30B2 are opened in step S4. Vents 30B3 and 30B4 are closed. Among the vents 30C1 to 30C3, vents 30C1 and 30C2 are opened in step S4. Vent 30C3 is closed.

[0041] Due to the suction by the exhaust fan 71, the pressure in the ventilation path 36 communicating with the opened vent 30 decreases, and a negative pressure is generated in the ventilation path 36 (step S5). Specifically, a negative pressure is generated in the ventilation paths 36A1, 36A2, 36B1, 36B2, 36C1, and 36C2.

[0042] Among the ventilation paths 36A1 to 36A3, the ventilation path 36A1 connected to the vent 30A1 located at the tip 24 preferentially allows gas to flow. The ventilation of the ventilation path 36A1 is started prior to starting the ventilation of the ventilation path 36A3 connected to the front (closer to the inlet 21) vent 30A3. The gas flow in each ventilation path 36 is adjusted so as to generate a gas flow in the ventilation path 36A1 prior to the ventilation path 36A3.

[0043] Among the ventilation paths 36B1 to 36B4, the ventilation path 36B2 connected to the vent 30B2 located in the upper concave portion 25 preferentially allows gas to flow. The ventilation of the ventilation path 36B2 is started prior to starting the ventilation of the ventilation paths 36B3 and 36B4 connected to the front vents 30B3 and 30B4. The gas flow in each ventilation path 36 is adjusted so as to generate a gas flow in the ventilation path 36B2 prior to the ventilation paths 36B3 and 36B4.

[0044] Among the ventilation passages 36C1 to 36C3, the ventilation passage 36C2 connected to the vent 30C2 located at the confluence portion 26 is preferentially flowed with gas. The ventilation of the ventilation passage 36C2 is started prior to starting the ventilation to the ventilation passage 36C3 connected to the front vent 30C3. The flow of the gas in each ventilation passage 36 is adjusted so as to generate a flow of gas in the ventilation passage 36C2 prior to the ventilation passage 36C3.

[0045] The pressure sensor 52 detects the air pressure in the ventilation pipe 50 communicating with the ventilation passage 36. When the pressure value detected by the pressure sensor 52 becomes equal to or less than the threshold value, the opening of the blow nozzle 12 is opened to start filling the casting sand into the hollow space 22 (step S6).

[0046] The casting sand and the pressurized gas are supplied into the hollow space 22. The pressurized gas flows toward the ventilation passage 36 where a negative pressure is generated, and the casting sand moves in the hollow space 22 along the flow of the pressurized gas. Since the vents 30A1 and 30A2 at the tip portion 24 of the hollow space 22 are opened and a negative pressure is generated in the ventilation passages 36A1 and 36A2, the casting sand flows together with the gas toward the vents 30A1 and 30A2. Then, the casting sand gradually fills the hollow space 22 from the tip portion 24 (step S7).

[0047] When the tip portion 24 is filled with the casting sand, the vent 30A1 is blocked by the filled casting sand. The flow of the pressurized gas trying to flow from the hollow space 22 into the ventilation passage 36A1 via the vent 30A1 is blocked by the filled casting sand. When the suction by the exhaust fan 71 is continued in this state, the pressure in the ventilation passage 36A1 decreases, and the pressure in the ventilation pipe 50 connected to the ventilation passage 36A1 also decreases. When the pressure value in the ventilation pipe 50 detected by the pressure sensor 52 becomes 1 to 20% lower than the peak value, it is determined that the tip portion 24 is clogged with sand, and the front vent 30A3 is opened (step S8).

[0048] The vent 30A3 that was closed in step S4 is opened in step S8. Similarly, the vents 30B3, 30B4, and 30C3 that were closed in step S4 are opened in step S8. After generating a gas flow in the air passages 36A1, 36B2, 36C2 in step S4, a gas flow is generated in the air passages 36A3, 36B3, 36B4, 36C3 in step S8. The gas flow is adjusted so that the ventilation of the air passages 36A1, 36B2, 36C2 is started in step S4 and the ventilation of the air passages 36A3, 36B3, 36B4, 36C3 is started in the subsequent step S8. Due to the suction by the exhaust fan 71, the pressure in the air passage 36 communicating with the opened vent 30 decreases, and a negative pressure is generated in the air passage 36.

[0049] Since the vent 30A3 is opened and a negative pressure is generated in the air passage 36A3, it becomes easier for the molding sand to flow together with the gas toward the vent 30A3. The molding sand is filled in the hollow space 22 without gaps.

[0050] When all the vents 30 are opened and the filling of the molding sand into all the vents 30 is completed, the supply of the molding sand and the pressurized gas into the hollow space 22 is terminated (step S9).

[0051] FIG. 7 is a chart showing an example of the time change of the pressure value (atmospheric pressure) in the ventilation pipe 50 detected by the pressure sensor 52. The horizontal axis in FIG. 7 is time, and the vertical axis is atmospheric pressure. In FIG. 7, the temporal transitions of the detection results of the pressures in the three ventilation pipes 50 respectively communicating with the vents 30A1, 30A2, 30A3 are shown. The label A1 shown in FIG. 7 indicates the detection result of the pressure by the pressure sensor 52 in the ventilation pipe 50 communicating with the vent 30A1. The label A2 indicates the detection result of the pressure by the pressure sensor 52 in the ventilation pipe 50 communicating with the vent 30A2. The label A3 indicates the detection result of the pressure by the pressure sensor 52 in the ventilation pipe 50 communicating with the vent 30A3.

[0052] At time T0, vents 30A1 and 30A2 are opened and vent 30A3 is closed (corresponding to step S4 in FIG. 6). By sucking the gas in the ventilation passages 36A1 and 36A2, the pressure in the ventilation passages 36A1 and 36A2 decreases (corresponding to step S5 in FIG. 6). At time T1, filling of the casting sand into the hollow space 22 is started (corresponding to step S6 in FIG. 6). By the pressurized air flowing into the ventilation passages 36A1 and 36A2, the pressure in the ventilation passages 36A1 and 36A2 increases.

[0053] At time T2, filling of the casting sand into the position of vent 30A1 is started, and at time T3, filling of the casting sand into the position of vent 30A2 is started (corresponding to step S7 in FIG. 6). Since the flow of the pressurized air trying to flow from the hollow space 22 into the ventilation passages 36A1 and 36A2 via vents 30A1 and 30A2 is blocked by the filled casting sand, the pressure in the ventilation passages 36A1 and 36A2 gradually decreases.

[0054] At time T4, filling of the casting sand into the position of vent 30A1 is completed and vent 30A3 is opened (corresponding to step S8 in FIG. 6). At time T5, filling of the casting sand into the position of vent 30A2 is completed. At time T6, filling of the casting sand into the position of vent 30A3 is completed (corresponding to step S9 in FIG. 6).

[0055] Returning to Fig. 6, after the filling is completed, the blow plate 13 is raised to separate the blow plate 13 from the mold body 20 (step S10). The mold body 20 is moved to the curing device 43, and the casting sand is cured by the curing gas (step S11). The mold body 20 is moved from the curing device 43 to the mold release workbench 42, the mold body 20 is split, and the core molded from the hollow space 22 is taken out (step S12). The quality of the taken-out core is checked (step S13). At this time, the data of the opening and closing timing of each vent 30 and the pressure change in the vent pipe 50 in steps S4, S5, S8, and S9 are recorded, and it can be confirmed that there is no defect such as a pressure drop due to leakage from the hollow space 22. By associating the data of the pressure change of each vent 30 with the data of the core determined to be defective as a result of the quality check, the filling conditions of the casting sand, specifically, the timing of opening and closing the vent 30 can be reviewed. The result of the core quality check is fed back to the filling conditions of the casting sand, and the filling conditions can be optimized.

[0056] As a result of the quality check, the cores determined to be good are shipped (step S14). In this way, a series of processes related to core molding are completed.

[0057] As described above, in the core molding apparatus 1 according to the embodiment, as shown in Fig. 2, a plurality of ventilation paths 36 serving as passages for the gas flowing out from the hollow space 22 are formed in the mold body 20. The flow of the gas in the ventilation path 36 can be individually adjusted for each ventilation path 36.

[0058] By actively controlling the flow of the sand in the hollow space 22, when there is a part where there is a concern about a defect such as sand clogging in the hollow space 22, the gas can be preferentially flowed to the part where there is a concern about a defect, and the casting sand can be preferentially supplied to the part where there is a concern about a defect by riding on the gas flow. Therefore, the sand clogging defect at the part where there is a concern about a defect can be reduced.

[0059] Conventionally, for cores with complex shapes where there is a concern about sand clogging, the cores were shaped manually. According to the embodiments of the present disclosure, there is no need to manually fill sand into the locations where problems are suspected, and the shaping of cores with complex shapes can be automated, so labor can be saved and productivity can be improved. Since sands with poor fluidity and prone to sand clogging can also be applied, the degree of freedom in sand selection is improved. The sand density after shaping can be made uniform, and the quality of the cores is stabilized, so the quality of the castings cast using the cores is improved.

[0060] As shown in FIG. 1, the core shaping device 1 includes a plurality of solenoid valves 61 for adjusting the flow rate of the gas flowing through each ventilation path 36. By appropriately controlling the plurality of solenoid valves 61, opening the solenoid valve communicating with the ventilation path 36 through which the gas flows and closing the solenoid valve communicating with the ventilation path 36 that is not the target for gas flow, the flow of the gas in the ventilation path 36 can be appropriately adjusted, and the casting sand can be surely supplied to the locations where problems are suspected.

[0061] As shown in FIG. 1, the core shaping device 1 further includes a plurality of ventilation pipes 50 equal in number to the ventilation paths 36. As shown in FIG. 3, each of the ventilation pipes 50 is individually communicated with any one of the plurality of ventilation paths 36. The gas flowing out from the hollow space 22 flows into the ventilation pipe 50 via the ventilation path 36. The path of the ventilation pipe 50 can be determined so as to flow the gas to an arbitrary position outside the mold body 20. The plurality of ventilation pipes 50 can be assembled in the solenoid valve unit 60 shown in FIG. 1.

[0062] As shown in FIG. 1, each solenoid valve 61 is provided on each of the ventilation pipes 50. By controlling the solenoid valve 61 outside the mold body 20, the flow of the gas in the ventilation path 36 communicating with the ventilation pipe 50 can be adjusted. It is not necessary to provide the solenoid valve 61 on the mold body 20. The ventilation pipe 50 provided with the solenoid valve 61 can be connected to the ventilation path 36 of an arbitrary mold body 20 to adjust the flow of the gas in the ventilation path 36. Since the same ventilation pipes 50 and solenoid valves 61 can be used for different mold bodies 20 for shaping cores with different shapes, the versatility of the core shaping device 1 can be improved and the cost can be reduced.

[0063] As shown in FIG. 1, the solenoid valve 61 opens and closes the ventilation pipe 50. By applying an inexpensive solenoid valve 61 capable of opening and closing the path, the cost of the core molding apparatus 1 can be reduced. By appropriately adjusting the timing of opening and closing of the solenoid valve 61, the gas flow in the ventilation path 36 can be individually adjusted for each ventilation path 36.

[0064] As shown in FIG. 3, a pressure sensor 52 is provided in each of the ventilation pipes 50. From the detection result of the pressure sensor 52, it can be determined that the hollow space 22 at the position where the ventilation path 36 communicating with the ventilation pipe 50 is connected is filled with molding sand. Based on the detection result of the pressure sensor 52, the gas flow in the ventilation path 36 can be switched. Instead of the pressure sensor 52, a flow meter for detecting the gas flow rate in the ventilation pipe 50 may be provided, but the pressure sensor 52 is less expensive and control based on pressure is easy.

[0065] From the detection results of the plurality of pressure sensors 52 provided in the plurality of ventilation pipes 50, it can be determined whether the sand is blocked in the middle of the hollow space 22. For example, when it is detected that the pressure in the ventilation pipe 50 communicating with the ventilation path 36A1 has decreased and gas starts to flow into the ventilation path 36A3, if the pressure in the ventilation pipe 50 communicating with the ventilation path 36A3 is substantially the same as the pressure in the ventilation pipe 50 communicating with the ventilation path 36A1, it can be determined that the hollow space 22 is blocked on the side closer to the inlet 21 than the vent 30A3.

[0066] The pressure in the ventilation pipe 50 can be detected outside the mold body 20, and the pressure sensor 52 does not have to be provided in the mold body 20. Since the same ventilation pipe 50 and pressure sensor 52 can be used for different mold bodies 20 for molding cores of different shapes, the versatility of the core molding apparatus 1 can be improved and the cost can be reduced.

[0067] By analyzing the pressure in the vent pipe 50 detected by the pressure sensor 52, the behavior of the molding sand when filling the mold body 20 with the molding sand can be visualized. The pressure in the vent pipe 50 detected by the pressure sensor 52 can be used as basic data for optimizing the suction timing for each vent passage 36 and other blowing conditions. This data can also be used to understand abnormal behavior during mass production of the cores. For example, by detecting pressure fluctuations with the pressure sensor 52 when sand clogs the vent 30 and the suction force decreases, or when gas leaks from the gaps in the mold body 20, the cleaning of the vent 30 can be carried out early, and the defect of molding low-quality cores can be suppressed.

[0068] As shown in FIG. 1, the core molding apparatus 1 further includes an exhaust fan 71 that sucks the gas in the vent passage 36. By generating a negative pressure in the hollow space 22 to create a gas pressure gradient, the fluidity of the molding sand can be improved. By individually optimizing the suction intensity or timing for each vent passage 36, the movement of the molding sand can be controlled more actively.

[0069] As shown in FIG. 2, a gas flow is generated in the vent passage 36A1 connected to the tip portion 24, ahead of the vent passage 36A3 connected closer to the inlet 21, which is the inlet of the molding sand into the hollow space 22 than the vent passage 36A1. By changing the timing of generating the gas flow in the vent passages 36A1 and 36A3 and adjusting the gas flow so that the ventilation of the vent passage 36A3 starts after the ventilation of the vent passage 36A1 starts, the movement of the molding sand to the tip portion 24 connected to the vent passage 36A1 is promoted. Thereby, the molding sand can be surely filled in the tip portion 24, and the sand clogging defect at the tip portion 24 can be reduced.

[0070] As shown in FIG. 2, a gas flow is generated in the ventilation passage 36B2 connected to the upper concave portion 25, ahead of the ventilation passages 36B3 and 36B4 connected near the introduction port 21 which is the inlet of the casting sand into the hollow space 22 rather than the ventilation passage 36B2. By changing the timing of generating the gas flow in the ventilation passages 36B2, 36B3, and 36B4 and adjusting the gas flow so that the ventilation of the ventilation passages 36B3 and 36B4 is started after the ventilation of the ventilation passage 36B2 is started, the movement of the casting sand to the upper concave portion 25 connected to the ventilation passage 36B2 is promoted. Thereby, the upper concave portion 25 can be surely filled with the casting sand, and the clogging defect in the upper concave portion 25 can be reduced.

[0071] As shown in FIG. 2, a gas flow is generated in the ventilation passage 36C2 connected to the confluence portion 26, ahead of the ventilation passage 36C3 connected near the introduction port 21 which is the inlet of the casting sand into the hollow space 22 rather than the ventilation passage 36C2. By changing the timing of generating the gas flow in the ventilation passages 36C2 and 36C3 and adjusting the gas flow so that the ventilation of the ventilation passage 36C3 is started after the ventilation of the ventilation passage 36C2 is started, the movement of the casting sand to the confluence portion 26 connected to the ventilation passage 36C2 is promoted. Thereby, the confluence portion 26 can be surely filled with the casting sand, and the clogging defect in the confluence portion 26 can be reduced.

[0072] <Second Embodiment> FIG. 8 is a diagram showing an outline of the configuration of the core molding apparatus 1 according to the second embodiment. Compared with the first embodiment shown in FIG. 1, the core molding apparatus 1 according to the second embodiment is different in that it does not include the exhaust fan 71 and the decompression chamber 72. That is, in the core molding apparatus 1 according to the second embodiment, the gas in the ventilation passage 36 and the ventilation pipe 50 is not sucked. The casting sand is filled into the hollow space 22 by supplying pressurized air from the blow head 11.

[0073] FIG. 9 is a flowchart showing the processing flow of the core molding method of the second embodiment. In steps S21 to S23 shown in FIG. 9, the same processing as steps S1 to S3 in the core molding method of the first embodiment shown in FIG. 6 is performed.

[0074] Subsequently, the vent 30 near the portion where a defect is suspected is opened (step S24). That is, the solenoid valve 61 communicating with the vent 30 to be opened via the ventilation path 36 and the ventilation pipe 50 is opened. Since there is no exhaust fan, suction in the ventilation path 36 is not performed. Without waiting for the generation of negative pressure in the ventilation path 36, the filling of the casting sand into the hollow space 22 is immediately started (step S25). The pressurized gas flows toward the opened vent 30, and the casting sand moves in the hollow space 22 along the flow of the pressurized gas. Since the vent 30A3 is closed and the vents 30A1 and 30A2 are opened, the casting sand flows together with the gas toward the vents 30A1 and 30A2. Then, the casting sand moves to the tip portion 24 (step S26).

[0075] When the tip portion 24 is filled with the casting sand, the filled casting sand blocks the vent 30A1. The flow of the pressurized gas that tries to flow from the hollow space 22 into the ventilation path 36A1 via the vent 30A1 is blocked by the filled casting sand. The flow rate of the pressurized gas flowing from the hollow space 22 into the ventilation path 36A1 decreases, so that the pressure in the ventilation path 36A1 drops. When the pressure value in the ventilation pipe 50 detected by the pressure sensor 52 becomes 1 to 20% lower than the peak value, the front vent 30A3 (closer to the inlet 21) is opened (step S27).

[0076] In subsequent steps S28 to S33, the same processing as steps S9 to S14 shown in FIG. 6 is performed.

[0077] Even if the gas in the ventilation path 36 is not sucked by the suction device, the opening and closing of the vent 30 can be switched at an appropriate timing to control the flow of the pressurized gas into the ventilation path 36. The core can be molded so that the casting sand fills the hollow space 22 without gaps, thereby reducing the risk of sand clogging.

[0078] In the core molding method of the first and second embodiments, an example has been described in which after filling the mold body 20 with casting sand using gas-curable sand, the casting sand is cured with a curing gas (steps S11, S30). Instead of gas-curable sand, self-hardening sand that cures with the passage of time may be used.

[0079] <Third Embodiment> FIG. 10 is a diagram showing an outline of the configuration of the core molding apparatus 1 according to the third embodiment. Compared with the first embodiment shown in FIG. 1, the core molding apparatus 1 according to the third embodiment is different in that it further includes a ventilator 81 and an accumulator 82. In addition to being able to suck the gas in the ventilation path 36 and the ventilation pipe 50 described in the first embodiment, the core molding apparatus 1 according to the third embodiment is configured to be able to flow gas from the ventilator 81 toward the vent 30 and reverse-inject the gas from the ventilation path 36 into the hollow space 22.

[0080] As shown in FIG. 10, the ventilator 81 and the accumulator 82 are connected to the solenoid valve unit 60. Although shown in a simplified manner in FIG. 10, for each solenoid valve 61 and the ventilation pipe 50 connected to the solenoid valve 61, either suction by the exhaust fan 71 or reverse injection by the ventilator 81 can be selectively applied.

[0081] For example, for the purpose of improving the sand clogging defect at the tip 24B shown in FIG. 2, while sucking from the vent 30B1, gas can be reverse-injected from the ventilation pipe 50 connected to the vent 30C1 to form a gas flow from the vent 30C1 toward the vent 30B1. By the action of this reverse injection, the casting sand with reduced fluidity at the bent portion 28 where the flow direction of the casting sand suddenly changes can be efficiently guided to the tip 24B, and the tip 24B can be filled with the casting sand, reducing the sand clogging defect. When the casting sand is filled up to the vent 30B4, the suction of the vent 30C1 is switched, and the filling of the casting sand into the hollow space 22 is completed.

[0082] After removing the shaped core from the mold 20, gas can be reverse-injected into all the vents 30. In this way, even if molding sand is trapped on the side of the hollow space 22 of the slit or mesh of the vent 30 during the filling of the molding sand, the trapped molding sand can be blown away for cleaning. Since the core molding apparatus 1 with the vent 30 cleaned can be used for the next core molding, quality control of the core becomes easier. Since the cleaning of the vent 30 can be automated, there is no need for an operator to clean it manually, and it can be efficiently cleaned in a short time.

[0083] <Fourth Embodiment> In the fourth embodiment, an example will be described in which molding sand is supplied to the hollow space 22 of the mold 20 from the blow head 11 in multiple divided portions. Usually, core molding is completed by one filling of molding sand into the mold 20, but at a location where the hollow space 22 suddenly becomes narrow, the molding sands collide with each other and the flow of the molding sand is suppressed. In order to avoid the collision of the molding sands, it is conceivable to reduce the ratio of the molding sand in the mixed molding sand and gas, but there are cases where the molding sand with a small diameter and high fluidity flows first and blocks the vent at the tip, suppressing the flow of the molding sand. Since the contact and pushing of the molding sands against each other also have the effect of improving the filling property, it is not desirable to reduce the ratio of the molding sand in the mixed molding sand and gas too much. A method of supplying the molding sand to the hollow space in multiple divided portions while maintaining the ratio of the molding sand sufficiently can compensate for the above-mentioned drawbacks.

[0084] FIG. 11 is a first diagram showing a process of supplying molding sand in divided portions. In the mold 20 shown in FIG. 11 and FIGS. 12 to 15 described later, an L-shaped hollow space 22 is formed. A total of 10 vents 30D1 to 30D10 are provided in the hollow space 22. In FIGS. 11 to 15, among the vents 30D1 to 30D10, the white squares indicate the vents 30 in the open state, and the black squares indicate the vents 30 in the closed state.

[0085] The casting sand supply device is configured to be able to adjust the supply amount of casting sand to the hollow space 22 in addition to switching the supply and stop of the casting sand to the hollow space 22 of the mold body 20. For example, a plurality of pressurized gas supply paths are arranged and connected to the blow head 11 at intervals in the vertical direction, and the pressurized gas can be selectively supplied into the blow head 11 from any one of the plurality of pressurized gas supply paths, so that the amount of casting sand falling from the blow head 11 to the mold body 20 can be adjusted.

[0086] In FIG. 11, the vents 30D1 and 30D2 are open, and the other vents 30D3 to 30D10 are closed. Along with the flow of the pressurized gas passing through the vents 30D1 and 30D2, the casting sand is carried toward the vents 30D1 and 30D2. In the first split supply, when the casting sand is filled in the hollow space 22 without gaps from the tip of the hollow space 22, the vents 30D1 and 30D2 are closed, but the casting sand in an amount that does not close the vent 30D3 before that is supplied into the hollow space 22.

[0087] FIG. 12 is a second diagram showing the process of split-supplying the casting sand. The casting sand supplied in the first split supply is clogged inside the hollow space 22 from the tip of the hollow space 22. The casting sand closes the vents 30D1 and 30D2. The vents 30D1 and 30D2 are closed. The vents 30D3 and 30D4 are open. The other vents 30D5 to 30D10 are closed.

[0088] Along with the flow of the pressurized gas passing through the vents 30D3 and 30D4, the casting sand is carried toward the vents 30D3 and 30D4. In the second split supply, when the casting sand is filled in the hollow space 22 without gaps from the tip of the hollow space 22 in combination with the amount supplied in the first split supply, the vents 30D1 to 30D4 are closed, but the casting sand in an amount that does not close the vent 30D5 before that is supplied into the hollow space 22.

[0089] Figure 13 is a third diagram showing the process of dividing and supplying molding sand. The molding sand supplied in the first and second divided supplies is clogged inside the hollow space 22 from the tip of the hollow space 22. The molding sand blocks vents 30D1 to 30D4. Vents 30D1 to 30D4 are closed. Vents 30D5 and 30D6 are open. The other vents 30D7 to 30D10 are closed.

[0090] Along with the flow of the pressurized gas flowing through vents 30D5 and 30D6, the molding sand is carried towards vents 30D5 and 30D6. In the third divided supply, if the molding sand is filled without gaps from the tip of the hollow space 22 in combination with the amounts supplied in the first and second divided supplies, vents 30D1 to 30D6 are closed, but vent 30D7 immediately before that is not closed, and an amount of molding sand is supplied into the hollow space 22.

[0091] Figure 14 is a fourth diagram showing the process of dividing and supplying molding sand. The molding sand supplied in the first to third divided supplies is clogged inside the hollow space 22 from the tip of the hollow space 22. The molding sand blocks vents 30D1 to 30D6. Vents 30D1 to 30D6 are closed. Vents 30D7 and 30D8 are open. The other vents 30D9 and 30D10 are closed.

[0092] Along with the flow of the pressurized gas flowing through vents 30D7 and 30D8, the molding sand is carried towards vents 30D7 and 30D8. In the fourth divided supply, if the molding sand is filled without gaps from the tip of the hollow space 22 in combination with the amounts supplied in the first to third divided supplies, vents 30D1 to 30D8 are closed, but vents 30D9 and 30D10 immediately before that are not closed, and an amount of molding sand is supplied into the hollow space 22.

[0093] FIG. 15 is a fifth diagram showing the process of dividing and supplying molding sand. The molding sand supplied in the first to fourth divided supplies is clogged inside the hollow space 22 from the tip of the hollow space 22. The molding sand closes the vents 30D1 to 30D8. The vents 30D1 to 30D8 are closed. The vents 30D9 and 30D10 are open. In the fifth divided supply, the molding sand in an amount that fills the entire hollow space 22, combined with the amount supplied in the first to fourth divided supplies, is supplied into the hollow space 22.

[0094] In this way, by dividing the molding sand filled in the hollow space 22 into an appropriate amount and supplying it into the hollow space 22, and by opening and closing the vents 30 at appropriate positions according to the divided supply, the molding sand can be uniformly filled into the entire hollow space 22 without gaps. Thereby, the problem of sand clogging can be more reliably reduced. By making the blow head 11 that supplies the molding sand and the pressurized air to the mold body 20 have a specification that can measure an appropriate amount of molding sand, an appropriate amount of molding sand can be supplied into the hollow space 22 at an appropriate timing.

[0095] In the previous description, the core molding apparatus 1 including the exhaust fan 71 as a suction device for sucking the gas in the air passage 36 has been described. Instead of the exhaust fan 71, a suction pump may be used as the suction device. However, in efficiently performing the core molding by the core molding apparatus and the core molding method shown in the embodiments of the present disclosure, since the responsiveness of the suction device is important, it is preferable to use the exhaust fan 71 with higher responsiveness.

[0096] In the previous description, the core molding apparatus and the core molding method for filling the hollow space 22 of the mold body 20 with molding sand to mold a core have been described. The idea of the present disclosure is also applicable to any other apparatus that fills a powder into a space by riding on the gas flow.

[0097] Although the embodiments have been described as above, configurations that can be combined with each other among the configurations described in the embodiments may be appropriately combined. Also, the embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0098] 1 Neutron Molding Device, 4 Sand Tank, 5 Mixer, 6 Hopper, 7 Scaffold, 8 Fence, 11 Blow Head, 12 Blow Nozzle, 13 Blow Plate, 20 Mold Body, 21 Inlet, 22 Hollow Space, 24, 24A, 24B Tip, 25 Upper Concave Portion, 26 Confluence Portion, 27 Narrow Portion, 28 Bending Portion, 29 Upstream Portion, 30, 30A1 to 30A3, 30B1 to 30B4, 30C1 to 30C4, 30D1 to 30D10 Vent, 36, 36A1 to 36A3, 36B1 to 36B4, 36C1 to 36C3 Vent Passage, 38 Opening, 41 Mold Base, 42 Mold Removal Workbench, 43 Hardening Device, 44 Gas Port, 50 Vent Pipe, 52 Pressure Sensor, 60 Solenoid Valve Unit, 61 Solenoid Valve, 71 Exhaust Fan, 72 Vacuum Chamber, 81 Blower, 82 Accumulator.

Claims

1. A mold body having a hollow space formed therein, and a molding sand supply device that mixes molding sand and gas and supplies the mixture to the hollow space, wherein a plurality of ventilation passages serving as passages for the gas flowing out from the hollow space are formed in the mold body, the flow of the gas in the ventilation passages can be individually adjusted for each of the ventilation passages, further comprising a plurality of flow rate adjustment valves for adjusting the flow rate of the gas flowing through each of the ventilation passages, the plurality of ventilation passages include a first ventilation passage connected to an upward concave portion where the upper surface of the hollow space is recessed upward, or a confluence portion where the molding sand flowing in the hollow space converges, and a second ventilation passage connected closer to the inlet of the molding sand into the hollow space than the first ventilation passage, a core molding device that adjusts the flow of the gas so that the flow of the gas is generated in the first ventilation passage prior to the second ventilation passage by opening the flow rate adjustment valve that adjusts the flow rate of the gas flowing through the first ventilation passage and closing the flow rate adjustment valve that adjusts the flow rate of the gas flowing through the second ventilation passage.

2. further comprising a plurality of ventilation pipes equal in number to the ventilation passages, each of the ventilation pipes being individually communicated with any one of the plurality of ventilation passages, the core molding device according to claim 1.

3. each of the flow rate adjustment valves is provided in each of the ventilation pipes, the core molding device according to claim 2.

4. the flow rate adjustment valve opens and closes the ventilation pipe, the core molding device according to claim 3.

5. further comprising a pressure sensor provided in each of the ventilation pipes and capable of detecting a pressure value in the ventilation pipes, the core molding device according to any one of claims 2 to 4.

6. further comprising a suction device that sucks the gas in the ventilation passages, the core molding device according to any one of claims 1 to 5.

7. the molding sand supply device can adjust the supply amount of the molding sand to the hollow space and supply the molding sand to the hollow space in a plurality of divided times, the core molding device according to any one of claims 1 to 6.

8. further comprising a blower that reversely injects gas from the ventilation passages into the hollow space, the core molding device according to any one of claims 1 to 7.

9. In a core molding method, molding sand and gas are mixed and supplied into a hollow space formed inside a mold body, and the mold body is formed with a first vent passage and a second vent passage that serve as passages for the gas flowing out from the hollow space. The first vent passage is connected to an upper concave portion where the upper surface of the hollow space is recessed upward, or a confluence portion where the molding sand flowing in the hollow space converges. The second vent passage is connected closer to the inlet of the molding sand into the hollow space than the first vent passage. A core molding method for adjusting the gas flow, in which after starting ventilation to the first vent passage by opening a flow rate adjustment valve for adjusting the flow rate of the gas flowing through the first vent passage and closing a flow rate adjustment valve for adjusting the flow rate of the gas flowing through the second vent passage, the flow rate adjustment valve for adjusting the flow rate of the gas flowing through the second vent passage is opened to start ventilation to the second vent passage.

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