Gas pressure control device

Abstract

To provide a gas pressure control device capable of controlling the pressure applied to the surface of a molten metal at high precision.SOLUTION: A gas pressure control device 1 comprises: a gas generation part 10 for generating a nitrogen gas; and a pressure control part 20 for adjusting the pressure of the nitrogen gas generated in the gas generation part 10 to feed the same to a low pressure casting device 50. The pressure control part 20 comprises: a servo valve 23 for controlling the flow rate of the nitrogen gas fed from a tank 17 to flow the same to the low pressure casting device 50; and a pressure controller 29 for adjusting the opening degree of the servo valve 23 based on the measuring pressure Pm of the nitrogen gas fed to the low pressure casting device.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas pressure control device suitable for generating a differential pressure between the internal space of a holding furnace for holding molten metal and the cavity of a casting mold to supply the molten metal in the holding furnace to the cavity.

Background Art

[0002] In an apparatus for casting using the differential pressure between a holding furnace and the cavity of a casting mold, for example, a low-pressure casting apparatus, molten metal is supplied to the holding furnace, and after repeating casting a predetermined number of shots, new molten metal is supplied to the holding furnace in preparation for the next casting. In a low-pressure casting apparatus, since the supply of molten metal is batchwise, when the number of casting shots increases, the molten metal level in the holding furnace drops. Therefore, even if the pressure for filling the cavity with molten metal is available in the first shot, the pressure decreases as the number of shots increases. Therefore, as disclosed in Patent Document 1 for example, it is necessary to perform subsequent casting with a corrected pressure in which the pressure applied to the molten metal is increased corresponding to the amount by which the molten metal level drops. The accuracy of the corrected pressure affects the quality of the cast product.

[0003] Patent Document 2 discloses using a servo valve to control the gas pressure for pressurizing the surface of molten metal. Patent Document 2 states that this gas pressurization control servo valve enables stepwise pressure increase of the gas pressure corresponding to each stage of filling the cavity of the casting mold with molten metal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a gas pressure control device capable of controlling the pressure applied to the surface of the molten metal with high precision.

Means for Solving the Problems

[0006] The gas pressure control device of the present invention includes a gas generation unit that generates nitrogen gas, and a pressure control unit that adjusts the pressure of the nitrogen gas generated by the gas generation unit and supplies it to a low-pressure casting device. The gas generation unit includes a separator that separates and extracts nitrogen gas from the taken-in air, and a tank that stores the nitrogen gas extracted by the separator. The pressure control unit includes a servo valve that controls the flow rate of the nitrogen gas supplied from the tank and flows it toward the low-pressure casting device, and a pressure controller that adjusts the opening degree of the servo valve based on the measured pressure of the nitrogen gas supplied to the low-pressure casting device.

[0007] The pressure controller preferably compares the measured pressure with the target pressure of nitrogen gas in the low-pressure casting device, and adjusts the opening degree of the servo valve corresponding to the difference between the measured pressure and the target pressure.

[0008] The pressure controller preferably holds casting pressure pattern data in which the elapsed time from the start to the completion of the supply of nitrogen gas to the low-pressure casting device and the target pressure corresponding to the elapsed time are associated, and compares the measured pressure with the casting pressure pattern data.

[0009] The pressure controller preferably holds casting pressure pattern data corresponding to each of a plurality of types of molds used in the low-pressure casting device, extracts the casting pressure pattern data corresponding to the mold when the plurality of types of molds are specified, and compares it with the measured pressure.

[0010] The pressure control unit preferably includes a pressure reducer that reduces the pressure of the nitrogen gas supplied to the servo valve and flows it toward the servo valve.

[0011] The gas generation unit and the pressure control unit are preferably housed in a common housing. Further, the pressure control unit preferably further includes a flow path that controls the flow rate of the nitrogen gas supplied from the tank and directs it to a target other than the low-pressure casting apparatus.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a gas pressure control device capable of controlling the pressure applied to the surface of the molten metal with high precision.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The gas pressure control device 1 according to the embodiment controls the pressure of nitrogen gas separated from air (hereinafter sometimes referred to as air) supplied from a supply source, and supplies it to a low-pressure casting device 50 as an example of a supply destination. The gas pressure control device 1 according to the present embodiment can control the pressure of nitrogen gas with high precision by performing feedback control on the servo valve 23. Hereinafter, after explaining the configuration of the gas pressure control device 1 and the configuration of the low-pressure casting device 50, the casting operation of the low-pressure casting device 50 using nitrogen gas whose gas pressure is controlled will be described.

[0015] [Gas pressure control device 1: Figure 1] As shown in FIG. 1, the gas pressure control device 1 includes a gas generation unit 10 that separates and generates nitrogen gas from air, and a pressure control unit 20 that controls the pressure of the nitrogen gas generated by the gas generation unit 10. The gas generation unit 10 includes a connection port 11 that receives air from a supply source, an impurity removal machine 13 that removes impurities from the air supplied from the connection port 11, a separator 15 that separates nitrogen gas from the air from which impurities have been removed by the impurity removal machine 13, and a tank 17 that stores the nitrogen gas separated by the separator 15. Note that the connection port 11 and the impurity removal machine 13, and between the impurity removal machine 13 and the separator 15 are connected by pipes, but the pipes are indicated by arrows in FIG. 1 and the like.

[0016] As the air supply source, an air supply source with a compressor installed in the factory where the gas pressure control device 1 and the low-pressure casting device 50 are provided is preferably used. This air supply source supplies air compressed in the range of, for example, 0.2 to 0.9 MPa.

[0017] The impurity removal machine 13 removes moisture, oil, and dust from the air. As the impurity removal machine 13, for example, a Reman dry filter is applied. This Reman dry filter includes, for example, a first element that separates moisture and oil from the compressed air from above, and a second element that includes a filter that removes solid particles in addition to moisture and oil from the air from which moisture and oil have been separated by the first element.

[0018] As the separator 15, as an example, a separation membrane method, a PSA (Pressure Swing Adsorption) method, and a cryogenic separator can be adopted. The separation membrane method includes a separation membrane composed of, for example, a bundle of polyimide hollow fibers. When compressed air is supplied to this separation membrane, it is separated into nitrogen gas and other gases during the process of passing through the inside of the hollow fibers. In addition, PSA gas separators include oxygen PSA that extracts oxygen from air and nitrogen PSA that extracts nitrogen. In this embodiment, nitrogen PSA is adopted. Nitrogen PSA utilizes the difference in the adsorption rates of oxygen and nitrogen of an adsorbent (Molecular Sieving Carbon) composed of a type of activated carbon. That is, pressurized air is sent into an adsorption tank filled with the adsorbent, and oxygen is preferentially adsorbed by the adsorbent, thereby separating nitrogen with higher purity than air and taking it out from the adsorption tank. The cryogenic separator 15 cools air, liquefies nitrogen (boiling point = -195.8°C), oxygen (boiling point = -183°C), and argon (boiling point = -185.7°C), and extracts high-purity gases based on the difference in their boiling points. The nitrogen separated from oxygen and the like by the separator 15 is stored in the tank 17 and supplied to the low-pressure casting device 50 according to the opening and closing operation of the servo valve 23. An oxygen concentration meter 19 for measuring the amount of oxygen contained in the nitrogen gas stored inside the tank 17 is provided in the tank 17, and the measurement result of the oxygen concentration meter 19 is sent to the separator 15.

[0019] Here, the oxygen concentration meter 19 is provided for the following first purpose and second purpose. First purpose: A guide for replacing the separator 15 If the concentration of oxygen contained in the separated nitrogen gas increases to a predetermined value or more, the life of the separator 15 is presumed. In that case, the separator 15 is replaced. Second purpose: Adjustment of the air supply amount to the separator 15 The separator 15 using the separation membrane method and the PSA method has a change in oxygen concentration depending on the supply amount of air. That is, when the supply amount of air is large, the oxygen concentration is high, which is due to oxygen molecules that cannot be completely separated and adsorbed passing through the separator 15 forcefully. On the other hand, when the supply amount is small, the oxygen concentration decreases, but in this case, the passing amount of nitrogen gas also decreases. Therefore, by measuring the oxygen concentration, the oxygen concentration can be suppressed, and a necessary amount of nitrogen gas can be supplied to the tank 17.

[0020] [Pressure control unit 20: Figure 1] Next, as shown in Figure 1, the pressure control unit 20 includes a pressure reducer 21 that reduces the nitrogen gas supplied from the tank 17 to a desired pressure, and a servo valve 23 that adjusts the flow rate of the nitrogen gas depressurized by the pressure reducer 21 and flows it downstream. The pressure control unit 20 includes a pressure gauge 25 that detects the pressure of the nitrogen gas flowing from the servo valve 23, and a discharge port 27 that discharges the nitrogen gas passing through the pressure gauge 25 toward the low-pressure casting apparatus 50. Further, the pressure control unit 20 includes a pressure controller 29 that controls the pressure of the nitrogen gas flowing downstream from the servo valve 23 by adjusting the opening degree of the servo valve 23, and a setter 31 that sets the pressure of the nitrogen gas controlled by the pressure controller 29.

[0021] Taking the nitrogen gas stored in the tank 17 as an example, the pressure reducer 21 adjusts it to 0.1 to 0.3 MPa and flows it toward the servo valve 23. This pressure is a value suitable for adjusting the pressure of the nitrogen gas required for the low-pressure casting apparatus 50. The specific means of the pressure reducer 21 is not limited as long as it can adjust this pressure.

[0022] The servo valve 23 adjusts the pressure of the nitrogen gas according to the change in the pressure of the nitrogen gas inside the pressurizing chamber 70 that stores the molten metal of the low-pressure casting apparatus 50 described later, and flows it downstream. The servo valve 23 can control this pressure adjustment with high precision and in multiple steps by adjusting the flow rate of nitrogen gas. That is, the pressure of nitrogen gas inside the pressurizing chamber 70 changes subtly due to the rise of the molten metal, the change in the height of the molten metal surface, the temperature inside the pressurizing chamber 70, the stalk 80, etc. On the other hand, in order to obtain high-quality castings with the low-pressure casting apparatus 50, it is desirable to correct this pressure change and realize a flow rate of the molten metal that matches or approximates the required ideal pressure change. Therefore, the gas pressure control device 1 controls the flow rate of the molten metal by adjusting the pressure of the nitrogen gas supplied to the low-pressure casting apparatus 50 by using the servo valve 23. This control of the molten metal is executed inside the mold according to the shape and dimensions of the casting.

[0023] The pressure gauge 25 is provided downstream of the servo valve 23 and measures the pressure of the nitrogen gas flowing from the servo valve 23. The measured pressure Pm is provided to the pressure controller 29.

[0024] The pressure controller 29 adjusts the opening degree of the servo valve 23 based on the measured pressure Pm of the nitrogen gas measured by the pressure gauge 25. This adjustment is performed by feedback control by comparing the measured pressure Pm with the casting pressure pattern set for the casting produced by the low-pressure casting apparatus 50 that the pressure controller 29 has. For this purpose, the pressure controller 29 holds the casting pressure pattern data. The casting pressure pattern data (hereinafter simply referred to as the casting pressure pattern) is data in which the elapsed time Tc from the start to the end of casting and the target pressure Pt of the nitrogen gas set for the casting are associated with each other for the casting. The casting pressure pattern is set according to the types of castings with different dimensions and shapes. The casting and the mold correspond one-to-one. Therefore, the pressure controller 29 stores the casting pressure pattern in association with a plurality of types of molds. Note that the operation of the pressure controller 29 may also be controlled by a higher-level control device 40. The higher-level control device 40 may also control the operation of the low-pressure casting device 50. Further, the opening degree of the servo valve 23 can also be adjusted based on an external pressure gauge, for example, a pressure gauge installed in the low-pressure casting device 50. This is a necessary measure to avoid response delay when the pipe connecting the discharge port 27 and the low-pressure casting device 50 is long.

[0025] An example of the casting pressure pattern will be described based on FIG. 2. In this example, the process from the start to the end of casting is divided into 11 stages from the 0th stage at the start of casting to the 10th stage at the end of casting as shown in FIGS. 2(a) and 2(b). For each of these 11 stages, the elapsed time from the start of casting and the pressure of the nitrogen gas are associated. For example, in the 1st stage, it is associated that when the elapsed time from the start of casting is 1 sec., the target pressure Pt of the nitrogen gas is 9 kPa. Also, in the 5th stage, it is associated that when the elapsed time from the start of casting is 5 sec., the target pressure Pt of the nitrogen gas is 18 kPa. Further, in the 7th stage, it is associated that when the elapsed time from the start of casting is 5 sec., the target pressure Pt of the nitrogen gas is 80 kPa. And in the 9th stage, it is associated that when the elapsed time from the start of casting is 9 sec., the target pressure Pt of the nitrogen gas is 0 kPa. Note that the casting pressure pattern in FIG. 2(a) includes the stroke 80 of the low-pressure casting device 50 and regions A to F in the cavity 95 of the mold 90, which will be described later, and the passage of the molten metal M through regions A to F can be understood. Regions A to F are shown in FIG. 4.

[0026] Here, the casting pressure pattern is adjusted according to the change in the cross-sectional area of the flow path through which the molten metal M passes. The cross-sectional area varies in regions A to F as will be described below. The flow path through which the molten metal M passes here includes the stroke 80, the runner 98, the gate 97, and the cavity 95. The first stage (region A) is a flow path through which the molten metal M passes inside the stalk 80, and its cross-sectional area is A. A Moreover, the relationship between the elapsed time Tc and the target pressure Pt of the nitrogen gas during this period is specified by the following equation (1) in FIGS. 2(a) and (b). Pt = A × Tc... Equation (1) 0 ≦ Pt ≦ 9 (kPa), 0 < Tc ≦ 1 (sec.)

[0027] The second stage (region B) is the runner 98 of the molten metal M (see FIG. 4) at the lowermost end inside the fixed mold 91, which is continuous with the upper limit position of region A. Its cross-sectional area is A. B However, it decreases from the lower limit position to the upper limit position. Moreover, the relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equation (2) in FIGS. 2(a) and (b). Pt = B × Tc... Equation (2) 9 < Pt ≦ 11 (kPa), 1 < Tc ≦ 2 (sec.) As shown in FIG. 2(b), the pressure from the first stage to the second stage rises linearly in proportion to the elapsed time, but this is merely an example. For example, the pressure in this section may rise in a curved shape, or the pressure in this section may rise stepwise in a staircase shape.

[0028] The third stage (region C) is the gate 97 of the molten metal M inside the fixed mold 91 (see FIG. 4), which is continuous with the upper limit position of region B. Its cross-sectional area is A. C Moreover, the relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equation (3) in FIGS. 2(a) and (b). Pt = C × Tc... Equation (3) 11 < Pt ≦ 12 (kPa), 2 < Tc ≦ 3 (sec.)

[0029] The fourth stage (region D) is the lower cavity 95L of the cavity 95 inside the fixed mold 91, which is continuous with the upper limit position of region C. Its cross-sectional area is A. DHowever, it increases from the lower limit position toward the upper limit position. Also, the relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equation (4) in FIGS. 2(a) and 2(b). Pt = D × Tc … Equation (4) 12 < Pt ≤ 16 (kPa), 3 < Tc ≤ 4 (sec.)

[0030] The fifth stage (region E) is the central cavity 95M among the cavities 95 inside the fixed die 91, which is continuous with the upper limit position of region D. Its passage cross-sectional area is A E However, it increases from the lower limit position toward the upper limit position. Also, the relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equation (5) in FIGS. 2(a) and 2(b). Pt = E × Tc … Equation (5) 16 < Pt ≤ 18 (kPa), 4 < Tc ≤ 5 (sec.)

[0031] The sixth stage (region F) is the upper cavity 95U among the cavities 95 that span both the inside of the fixed die 91 and the movable die 93, which is continuous with the upper limit position of region E. Its passage cross-sectional area is A F However, it increases from the lower limit position toward the upper limit position. Also, the relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equation (6) in FIGS. 2(a) and 2(b). In this embodiment, the molten metal M is filled into the cavity 95 formed between the fixed die 91 and the movable die 93 in the sixth stage. Pt = F × Tc … Equation (6) 18 < Pt ≤ 21 (kPa), 5 < Tc ≤ 6 (sec.)

[0032] The seventh and eighth stages are the first pressure-holding process that produces a pressure-pushing effect on the solidification shrinkage of the molten metal M by continuing to apply a high pressure, for example, 80 MPa, with nitrogen gas after the filling of the molten metal M. At the same time, as shown by the dashed line in FIG. 4, the center pin 96 is lowered to close the sprue 97. The relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equations (7) and (8) in FIGS. 2(a) and 2(b). The seventh stage Pt = G × Tc… Equation (7) 21 < Pt ≤ 80 (kPa), 6 < Tc ≤ 6.1 (sec) Eighth stage Pt = G… Equation (8) Pt = 80 (kPa), 6.1 < Tc ≤ 9 (sec)

[0033] In the ninth and tenth stages, after the descent of the center pin 96 is completed, the target pressure Pt is reduced to zero. As a result, the molten metal surface of the molten metal M in the stock 80 is lowered, and a second pressure holding process for pressurizing the molten metal M in the cavity 95 is performed using a pressurizing mechanism (not shown) incorporated in the mold 90. The second pressure holding process compensates for what is lacking in the first pressure holding process that depends only on the gas pressure. The relationship between the elapsed time Tc and the target pressure Pt during this period is specified by the following equations (9) and (10) in FIGS. 2(a) and (b). Ninth stage Pt = 0 (kPa)… Equation (9) Tc = 9 (sec) Tenth stage Pt = 0 (kPa)… Equation (10) 9 < Tc ≤ 10 (sec)

[0034] Where the cross-sectional area through which the molten metal M passes in this embodiment changes, that is, when transitioning from region A to region B, from region B to region C, from region C to region D, from region D to region E, and from region E to region F, the target pressure Pt of the nitrogen gas is changed. Thus, changing the target pressure Pt of the nitrogen gas where the cross-sectional area through which the molten metal M flows changes is for the following first to fourth purposes. First purpose: Appropriately control the flow rate of the molten metal according to the cross-sectional area, for example, prevent casting defects caused by turbulence of the molten metal such as air entrainment. Second objective: To address the situation where the air remaining in the cavity 95 of the mold 90 becomes a resistance and deteriorates the fluidity of the molten metal M. For example, as the molten metal M flows, the remaining air is gradually compressed and inhibits the molten metal flow. In particular, after the molten metal M passes through the split surface of the mold 90, the need increases because the locations where air can escape decrease. Also, for example, by adding vacuum suction to the mold 90, it becomes possible to reduce the air resistance. Third objective: To counteract the increase in the viscosity of the molten metal M due to the decrease in the temperature of the molten metal M and the resulting increase in the flow resistance. Fourth objective: To counteract the load of the weight of the molten metal M as the molten metal M rises due to the progress of filling. This applies to the case of vertical casting.

[0035] Next, the feedback control of the servo valve 23 by the pressure controller 29 will be described. This feedback control compares the measured pressure Pm of the nitrogen gas obtained by the pressure gauge 25 with the casting pressure pattern, and adjusts the opening degree of the servo valve 23 so that the measured pressure Pm matches the target pressure Pt of the casting pressure pattern. For example, during the first stage, that is, when the elapsed time Tc satisfies 0 < Tc ≤ 1, the measured pressure Pm and the target pressure Pt according to Equation (1) are compared. This comparison is performed by the pressure controller 29. If the measured pressure Pm is greater than the target pressure Pt, the pressure controller 29 closes the servo valve 23 by an amount corresponding to the difference. If the measured pressure Pm is less than the target pressure Pt, the pressure controller 29 opens the servo valve 23 by an amount corresponding to the difference. Further, if the measured pressure Pm matches the target pressure Pt, the pressure controller 29 maintains the opening degree of the servo valve 23.

[0036] The comparison between the measured pressure Pm and the target pressure Pt can also be performed by setting a threshold value for the target pressure Pt. For example, for the target pressure Pt = 9 kPa in the first stage, a threshold value of ±0.2 kPa is added, and the target pressure Pt for comparison with the measured pressure Pm can be in the range of 8.8 kPa to 9.2 kPa. In this case, if the measured pressure Pm is in the range of 8.8 kPa to 9.2 kPa, the pressure controller 29 regards the measured pressure Pm as being equal to the target pressure Pt. Also, if the measured pressure Pm is less than 8.8 kPa, the pressure controller 29 opens the servo valve 23 because the measured pressure Pm is less than the target pressure Pt. Furthermore, if the measured pressure Pm exceeds 9.2 kPa, the pressure controller 29 closes the servo valve 23 because the measured pressure Pm is greater than the target pressure Pt.

[0037] For the subsequent stages, the comparison between the measured pressure Pm and the target pressure Pt can be similarly performed to adjust the opening degree of the servo valve 23.

[0038] [Low-pressure casting device 50: Figures 3 and 4] Next, an example of the low-pressure casting device 50 will be described with reference to Figures 3 and 4. As shown in Figure 3, the low-pressure casting device 50 includes a holding furnace 60 for holding the molten metal M, a pressurizing chamber 70 that is communicated with the holding furnace 60 via the first communication path 81 and holds the molten metal M supplied from the holding furnace 60, and a stalk 80 that is communicated with the pressurizing chamber 70 via the second communication path 83. The upper end of the stalk 80 is connected to the opening of the fixed mold 91 that communicates with the cavity 95 of the mold 90 composed of the fixed mold 91 and the movable mold 93, and supplies the molten metal M to the cavity 95. Note that heaters (not shown) for heating the molten metal M in the holding furnace 60, the first communication path 81, and the second communication path 83 to the temperature required to maintain a molten state of about 500°C to 700°C are provided.

[0039] As shown in FIG. 3, the holding furnace 60 is provided with a stopper 61 that controls the supply of the molten metal M to the pressurizing chamber 70. The stopper 61 opens and closes the inlet to the first communication passage 81 of the holding furnace 60 so that a constant amount of the molten metal M is always accommodated inside the pressurizing chamber 70 at the start of the casting process.

[0040] As shown in FIG. 3, the upper end opening of the pressurizing chamber 70 is closed by a lid 75, and the upper surface space of the molten metal M in the pressurizing chamber 70 becomes a sealed space. The gas pressure control device 1 is connected to this sealed space via a gas inlet 71. The gas pressure control device 1 supplies nitrogen gas into the pressurizing chamber 70 via the gas inlet 71. Further, a molten metal level detection rod 73 is installed on the lid 75 facing the liquid level of the molten metal M. The molten metal level detection rod 73 detects whether or not the liquid level of the molten metal M in the pressurizing chamber 70 has reached a predetermined level when the molten metal M is sent from the holding furnace 60 to the pressurizing chamber 70.

[0041] [Casting operation of the low-pressure casting device 50: FIGS. 2, 5, and 6] Next, the casting operation of the low-pressure casting device 50 will be described with reference to FIGS. 2, 5, and 6. FIG. 5(a) shows the start point of casting, which shows the state at the 0th stage in FIGS. 2(a) and (b). When the elapsed time reaches 1 sec. after the start of casting, the opening degree of the servo valve 23 is adjusted so that the target pressure Pt becomes 9 kPa. Next, when the elapsed time reaches 2 sec., the opening degree of the servo valve 23 is controlled so that the target pressure Pt becomes 11 kPa. Next, when the elapsed time reaches 3 sec., the opening degree of the servo valve 23 is controlled so that the target pressure Pt becomes 12 kPa. At this time, as shown in FIGS. 5(b) and 4, the surface of the molten metal M reaches the lower limit of the region D.

[0042] Next, when the elapsed time reaches 4 sec., the opening degree of the servo valve 23 is controlled so that the target pressure Pt becomes 16 kPa, and when the elapsed time reaches 5 sec., the opening degree of the servo valve 23 is controlled so that the target pressure Pt becomes 18 kPa. At this point, as shown in FIGS. 6(a) and 4, the surface of the molten metal M reaches the lower limit of the region F. Further, when the elapsed time reaches 6 sec., the opening degree of the servo valve 23 is controlled so that the target pressure Pt becomes 21 kPa. At this point, as shown in FIGS. 6(b) and 4, the surface of the molten metal M reaches the upper limit of the region F, that is, the cavity 95 is filled with the molten metal M and reaches its upper limit.

[0043] After the surface of the molten metal M reaches the upper limit of the region F until the elapsed time reaches 6.1 sec., the opening degree of the servo valve 23 is adjusted so that the target pressure Pt becomes 80 kPa, and the state of 80 kPa is continued until the elapsed time reaches 9 sec. This step is performed to give the above-described effect of the pressing molten metal to the molten metal M.

[0044] When the elapsed time reaches 9 sec. and the step of pressing the molten metal is completed, the servo valve 23 is closed so that the target pressure Pt becomes zero, and the supply of nitrogen gas is stopped.

[0045] [Effect] Next, the effect of the gas pressure control device 1 according to the present embodiment will be described. In the gas pressure control device 1, the filling of the molten metal M in the low-pressure casting device 50 and the control of the pressure of the nitrogen gas during casting can be performed by feedback control by the servo valve 23. Therefore, according to the gas pressure control device 1, the control of the pressure of the nitrogen gas in multiple stages can be performed with high precision. Through this high-precision control, stable quality of the cast product obtained by the low-pressure casting device 50 can be obtained.

[0046] Further, according to the gas pressure control device 1, the target pressure Pt is changed according to the change in the cross-sectional area of the flow path of the molten metal M supplied to the mold 90. Thereby, the control of the pressure of the nitrogen gas suitable for the cast product can be performed with high precision.

[0047] Further, the gas pressure control device 1 includes a gas generation unit 10 that generates nitrogen gas and a pressure control unit 20 that controls the pressure of the generated nitrogen gas, and thus can be connected to and used with the low-pressure casting device 50. If the air supplied in the factory is used as the generation source of nitrogen gas, the gas pressure control device 1 can control the pressure of nitrogen gas without adding other configurations such as a nitrogen gas cylinder. That is, the gas pressure control device 1 has a self-contained device configuration. Further, if the gas generation unit 10 and the pressure control unit 20 are incorporated and housed in a single common housing, it can be quickly started to be used by moving to the position where it is used and connecting.

[0048] As described above, the present embodiment has been described. However, in addition to the above, as long as the gist of the present invention is not deviated from, it is possible to select the configurations listed in the above embodiment, or to appropriately change to other configurations. As an example thereof, the gas pressure control device 2 shown in FIG. 7 will be described. The gas pressure control device 2 includes a distributor 22 between the pressure reducer 21 and the servo valve 23 of the gas pressure control device 1, so as to utilize nitrogen gas for other devices of the low-pressure casting device 50. The gas pressure control device 2 further provides a distributor 22A in the flow path branched from the distributor 22, and the distributor 22A further branches the flow path into two in the downstream direction. Then, pressure reducers 21A and 21B are provided in each flow path, and flow rate control valves 23A and 23B are provided downstream of each of the pressure reducers 21A and 21B. Connection ports 27A and 27B are provided downstream of the flow rate control valves 23A and 23B so that nitrogen gas can be supplied from each to other usage targets. As an example of other uses, there are utilization of nitrogen gas for lowering the molten metal M inside the stalk 80 of the low-pressure casting device 50, utilization as degassing treatment and oxidation prevention treatment of the molten metal M, and the like.

[0049] The gas pressure control device 2 shown in FIG. 7 has a configuration different from that of the servo valve 23 and subsequent components of the gas pressure control device 1 in that it is provided downstream from the distributor 22A. However, in the present invention, it is also possible to include a plurality of servo valves 23 and subsequent components.

Explanation of reference numerals

[0050] 1 Gas pressure control device 10 Gas generation unit 11 Connection port 13 Impurity remover 15 Separator 17 Tank 19 Oxygen concentration meter 20 Pressure control unit 21 Pressure reducer 22 Distributor 23 Servo valve 25 Pressure gauge 27 Discharge port 29 Pressure controller 31 Setter 40 Control device 50 Low-pressure casting device 60 Holding furnace 61 Stopper 70 Pressure chamber 71 Gas inlet 73 Molten metal level detection rod 75 Cover 80 Stock 90 Mold 91 Fixed mold 93 Movable mold 95 Cavity 96 Center pin 97 Sprue 98 Runner M Molten metal

Claims

1. A gas generation unit that generates nitrogen gas, and a pressure control unit that adjusts the pressure of the nitrogen gas generated by the gas generation unit and supplies it to a low-pressure casting apparatus, wherein the gas generation unit comprises a separator that separates and extracts the nitrogen gas from the inhaled air, and a tank that stores the nitrogen gas extracted by the separator, and the pressure control unit comprises a servo valve that controls the flow rate of the nitrogen gas supplied from the tank and flows it toward the low-pressure casting apparatus, and a pressure controller that adjusts the opening degree of the servo valve based on the measured pressure of the nitrogen gas supplied to the low-pressure casting apparatus, and the pressure controller holds casting pressure pattern data set according to castings of different dimensions and shapes, and compares the measured pressure with the casting pressure pattern data. A gas pressure control device characterized by this.

2. The pressure controller compares the measured pressure with the target pressure of the nitrogen gas in the low-pressure casting apparatus, and adjusts the opening degree of the servo valve corresponding to the difference between the measured pressure and the target pressure. The gas pressure control device according to claim 1.

3. The casting pressure pattern data is associated with the elapsed time from the start to the completion of the supply of the nitrogen gas to the low-pressure casting apparatus and the target pressure corresponding to the elapsed time. The gas pressure control device according to claim 2.

4. The casting pressure pattern data corresponds to each of a plurality of types of molds used in the low-pressure casting apparatus. The gas pressure control device according to claim 3.

5. The pressure control unit comprises a pressure reducer that reduces the pressure of the nitrogen gas supplied to the servo valve and flows it toward the servo valve. The gas pressure control device according to any one of claims 1 to 4.

6. The gas generation unit and the pressure control unit are housed in a common housing. The gas pressure control device according to any one of claims 1 to 5.

7. The pressure control unit further comprises a flow path that controls the flow rate of the nitrogen gas supplied from the tank and flows it toward a usage target other than the low-pressure casting apparatus. The gas pressure control device according to any one of claims 1 to 6.

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