JPH11320072A - Differential pressure casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make controlled returning molten metal by reducing pressure in a cavity, sucking the molten metal through a molten metal supplying tube, filling it into the cavity, holding till solidified, and when passing the molten metal through the molten metal supplying tube and introducing a prescribed quantity of inert gas, releasing the pressure reduction of the cavity and opening the die. SOLUTION: The pressure in an air-tight chamber 4 is reduced from a communicating hole 4-3 with a pressure reducing device 8, and the molten metal 2 is filled up into the cavity 5-3 through a molten metal supplying tube 3. The tip part of a lance 6-1 is lowered to the position faced to the lower part of the molten metal supplying tube 3 after the elapse of time corresponding to the solidification and a valve is opened and the gas is pushed into the molten metal 2 with a fixed quantity gas supplying device. The gas if formed as bubble 6-3 and comes in the molten metal supplying tube 3 and raised to the solidified portion of a product and the unsolidified molten metal 2 is returned back into a molten metal vessel 1 according to the introducing gas. At the time of introducing the prescribed gas quantity, the pressure reduction of the air-tight chamber 4 is released and the die is opened and the product is taken out to complete the casting. Natural dropping is prevented the reduced pressure is kept also, the oxidation of the molten metal 2 is prevented with the inert gas atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a differential pressure casting method.

[0002]

2. Description of the Related Art Pressure differential pressure casting (low casting), in which a furnace is pressurized to press molten metal into a mold, and pressure reducing differential pressure casting, in which a mold is depressurized and a molten metal is sucked, are controlled by differential pressure, and the quality is controlled. Can provide good castings. In any case, the differential pressure is released when the casting is completed, and the unsolidified molten metal is returned to the furnace, so that the product yield is high. The decompression type is applied to thin-walled parts with few cores because of its excellent filling capacity, and the pressure type is appropriately used for other parts with many cores and super-large products.

[0003]

However, the conventional differential pressure casting method has the following problems. At the completion of casting, even if the differential pressure is released, an airtight state is formed between the product and the molten metal, the molten metal does not return, and falls when the airtightness is broken by die cutting or the like. As it falls a considerable height, the molten metal in the furnace is stirred,
Inclusions accumulated at the bottom are caught in the molten metal, or form oxides during the fall to form new inclusions. The inclusions entangled in the molten metal enter the product in the next casting and become defects. A filter such as a wire mesh is used to prevent this, but there are limitations. Attempts were made to release the differential pressure slowly to prevent natural fall, but this had no effect since the melt was airtight as described above. It has also been proposed to provide a closed space at a mold joining portion of a hot water supply pipe, provide a gas introduction hole therein, introduce a gas after completion of casting, and gently lower the molten metal in the hot water supply pipe. However, since the gas introduction hole in this mechanism is closed by the intrusion of the molten metal, a liquid level sensor that determines the upper limit of the molten metal level in the closed space is installed to prevent the intrusion of the molten metal. Also, during casting and holding, if gas leaks from this space, it will enter the product and cause gas defects, so a liquid level sensor that determines the lower limit of the molten metal level in the closed space is also installed, which is a problem for stable operation. Was. Also,
The hot water supply pipe of this structure has a complicated shape and has a problem in life and the like. In some cases, a porous gas inlet is provided near the gate of the mold, but there is a problem in durability due to direct contact with the molten metal and exposure to the air at each casting. Also,
Since it was set on the mold itself, it also affected the life of the mold. SUMMARY OF THE INVENTION An object of the present invention is to provide a differential pressure casting method capable of producing a controlled return hot water without changing the structure of a hot water supply system, for both a pressure type and a pressure reducing type. Another object of the present invention is to provide an inert atmosphere for preventing oxidation.

[0004]

The present invention to achieve the above object is as follows. (1) The cavity in the mold is depressurized, the molten metal in the molten metal container is sucked into the cavity via the hot water supply pipe, filled into the cavity in the mold, and maintained until the product solidifies, and then the inert gas is passed through the molten metal into the hot water supply pipe at a predetermined flow rate And a pressure-reducing differential pressure casting method comprising the steps of releasing the pressure in the cavity in the mold and opening the mold when a predetermined amount is introduced. (2) The molten metal is filled into the mold cavity via a hot water supply pipe communicating with the cavity in the mold by pressurizing the hermetic furnace, holding until the product solidifies, and then reducing the pressure in the hermetic furnace at a preset speed. At the same time, the inert gas is introduced into the hot water supply pipe at a predetermined flow rate at the same time as the pressure in the hermetic furnace reaches the atmospheric pressure, and the pressure in the hermetic furnace is raised to the atmospheric pressure. A pressure-type differential pressure casting method characterized in that the mold is opened and the product is taken out after reaching.

[0005] In the above method (1) or (2), the returning hot water, which could not be controlled only by the external pressure difference, can be completely controlled. It is possible to provide a gradual decrease in pressurization and the like, and to prevent a natural fall, thereby enabling a stable operation. In addition, by adopting a method that is applied to both pressure reduction and pressure application, it is possible to select a casting method according to the characteristics of the product as in the past. In addition, since the introduced gas floats in the molten metal, it is sufficiently heated from the molten metal and the temperature of the space above the hot water supply pipe is supplied through the molten metal from the case where it is directly introduced into the conventional space or from the vicinity of the upper space. There is an advantage that the hot water can be controlled only by the amount of gas and is more stable than the method of performing hot water refining. That is, a level sensor or the like inside the space is unnecessary. Further, the introduction of the gas is performed by changing the position of the lance, and there is no possibility that the gas is mixed during the casting to the holding, thereby solving the problem of the conventional fixed type introduction port. In addition, an inert gas for protecting the molten metal surface can be introduced into both the molten metal container and the hot water supply pipe. The gas introduction device is separate from the casting device such as a hot water supply pipe, and is excellent in maintainability. Further, the level of the molten metal in the molten metal container can be constantly measured from the back pressure by this gas introducing device. In the embodiment, the molten metal level is used for pressure control. Stable casting can be realized because of actual measurement. In addition, the gas introducing device itself can perform a self-diagnosis, detect an unexpected blockage or a sudden leak, and perform a stable operation. Furthermore, in test casting before mass production, since gas can be introduced into the mold cavity via the hot water supply pipe at a fixed time, the progress of product solidification can be reliably and continuously measured at the position of the trap bubble. In addition, degassing of the molten metal can be promoted.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A casting method according to an embodiment of the present invention will be described. FIG. 1 shows an embodiment in which the present invention is applied to a reduced-pressure differential pressure casting, and shows a case in which refilling is started upon completion of casting. In FIG. 1, 1 is a molten metal container (corresponding to a furnace in the case of pressurization), 2 is molten metal, 3 is a hot water supply pipe, and 4 is an airtight chamber. The airtight chamber 4 includes a surface plate 4-1 and an airtight box 4-
The communication port 4-3 is connected to a pressure reducing device such as a vacuum pump (not shown). 5 is a mold,
A cavity 5-3 is formed by the lower mold 5-1 and the upper mold 5-2 and communicates with the hot water supply pipe 3. 6 is a gas introduction device,
It comprises a blowing lance (hereinafter referred to as a lance) 6-1 and a lance moving mechanism 6-2 including a cylinder and the like. Reference numeral 7 denotes a control panel of the gas introduction device, which includes a pressurized inert gas source 8 and a lance 6
1 are connected. 6-3 indicates bubbles of the introduced gas. The control panel 7 receives a gas introduction start signal from a casting device (not shown).

FIG. 2 shows an embodiment in which the present invention is applied to a pressure differential pressure casting, and shows the same steps as in FIG. 2, the same numbers as those in FIG. 1 indicate the same contents. In FIG. 2, furnace 1
Constitutes an airtight structure with the surface plate 4-1. The pressurized gas inlet 1-1 is connected to a pressurized inert gas source 8 via a casting machine control panel 9. Reference numeral 6-5 denotes an insertion port of the lance 6-1 having a built-in airtight seal. FIG. 3 shows a situation other than the hot water return step in the case of the reduced pressure type. FIG. 4 shows the status of steps other than the hot water return step in the case of the pressure type.

FIG. 5 shows the contents of the control panel 7 of the gas introduction device of FIG. A control circuit 7-1 is constituted by an electronic circuit such as a CPU (Central Processor Unit), a memory, and a power supply, and inputs a gas introduction start signal from a control panel of the casting apparatus. The output of the control circuit 7-1 is output to the servomotor 7-2, connected to the on-off valves 7-4, 7-5, 7-8, and connected to the lance moving mechanism 6-2 of the gas introducing device 6. You. Reference numeral 7-3 denotes a fixed-quantity gas supply device, which has a built-in piston 7-31 and is driven by a servomotor 7-2. 7-7 is a pressure reducing valve, and 7-6 is a flow control valve. 7-9 is a pressure sensor for measuring the back pressure of the lance, and the output is input to the control circuit 7-1. The bold line in the figure indicates the path of the gas, and is connected to the lance 6-1 from the pressurized inert gas source 8 via the control panel 7 of the gas introduction device.

FIG. 6 shows the valves 7-4, 7-5, 7-8 of FIG.
FIG. 6 is an operation diagram showing the operation of the lance 6-1 for each process. O indicates open and X indicates closed, and "up" of the lance indicates that the tip is above the lower end of the hot water supply pipe, and "down" indicates that the position is directly below the hot water supply pipe and faces the inside of the hot water supply pipe. FIG.
The contents of the casting machine control panel 9 of the pressurized embodiment of FIG. 2 are shown.
The same numbers as those in FIG. 5 indicate the same contents. In the figure, reference numeral 9-1 denotes a pressure control device, which receives a setting signal from a pressure pattern generation circuit 9-2, receives a measurement signal from a pressure sensor 7-9, and supplies an air supply valve 9-3 and an exhaust valve 9. -4 is output. The setting signal from the pressure pattern generation circuit 9-2 is output to the control circuit 7-1. It is connected from the pressurized inert gas source 8 to the pressurized gas inlet 1-1 of the furnace 1 via the supply valve 9-3, and is also connected to the exhaust valve 9-4 at the same time. The pressure sensor 9-5 is arranged in front of the pressurized gas inlet 1-1, and the output is input to the pressurization control device 9-1. FIG.
FIG. 3 is a characteristic diagram showing a change in the degree of pressure reduction of the airtight chamber 4 and a change in the gas flow rate of the lance 6-1 in the case of the embodiment of FIG. FIG. 9 is a characteristic diagram showing a change in the internal pressure in the hermetic chamber 4 and a change in the flow rate of the lance 6-1 in the case of the embodiment of FIG.

Next, the operation will be described. In the embodiment of FIG. 1, before casting, the lance 6-1 is, as shown in FIG.
The tip is at a position outside the hot water supply pipe 3, and is in the "up" position in the mold opening step of FIG. At this time, the inert gas is supplied from the pressurized inert gas source 8 by the control panel 7 of the gas introduction device to the pressure reducing valve 7-7, the flow control valve 7-6, and the valve 7- in FIG.
The air is blown into the molten metal 2 in the molten metal container 1 by the lance 6-1 through the molten metal 8, and rises in the molten metal 2 as bubbles 6-3 and is discharged from the liquid surface. At this time, the pressure sensor 7-9 of the control panel 7 of the gas introducing device measures the back pressure of the lance 6-1 and outputs it to the control circuit 7-1. Since the back pressure at this time is proportional to the depth of the tip of the lance 6-1 in the molten metal 2, the liquid level in the molten metal 2 can be measured by fixing the position of the distal end. When the casting is continued, the molten metal 2 in the molten metal container 1 is reduced and the liquid level is lowered. Therefore, the measured value of the liquid level due to the back pressure is used for correcting the degree of pressure reduction and correcting gas introduction described later. The control circuit 7-1 obtains the amount of gas to be introduced from the liquid level measurement value from a preset arithmetic expression or a table, and obtains the quantitative gas supply device 7.
The stroke of the piston 7-31 is set, and the servo motor 7-2 moves the piston 7-31 backward. Further, the valve 7-5 is closed, and when the lance 6-1 is returned to the “up” position, the valve 7-4 is opened, and the fixed amount gas is supplied to the fixed amount gas supply device 7-3 by retreating the piston 7-31. Intake inert gas. Valve 7-4 closes after a sufficient time has elapsed.

[0011] Close the mold, cover the airtight box 4-2,
The pressure inside the airtight chamber 4 is reduced by the pressure reducing device 8 through the communication port 4-3, and the molten metal 2 is filled into the cavity 5-3 via the hot water supply pipe 3. After filling, the vacuum is maintained until the product solidifies. As shown in FIG. 1, the valve 7-8 in FIG. 5 is first closed and the lance 6-1 is placed immediately below the lower end of the hot water supply pipe 3 and the tip thereof is inserted into the hot water supply pipe 3 at a time corresponding to the product solidification set by a timer or the like. Lower to face. The valve 7-5 is opened, and the piston 7-31 of the gas quantitative supply device 7-3 is advanced by the servo motor 7-2 according to a preset pattern stored in the control circuit 7-1.
The gas is pushed out into the melt 2 via -1.

The extruded gas forms bubbles 6-3 and enters the hot water supply pipe 3 and rises to a solidified portion of the product, thereby forming a space balanced with the atmospheric pressure. As a result, the unsolidified molten metal of the hot water supply system including the hot water supply pipe 3 returns to the molten metal container 1 according to the amount of introduced gas. That is, the speed of the return hot water can be controlled by the amount of the introduced gas. At this time, the inside of the airtight chamber 4 is kept under reduced pressure. This is to prevent the hot water from being returned only by gas introduction and to prevent the natural fall due to an unexpected airtight leak. The degree of reduced pressure to be held may be the maximum pressure as it is, may be reduced to the equivalent of a gate, or may be gradually reduced to atmospheric pressure. In any case, it is sufficient that the degree of pressure reduction is equal to or higher than the molten metal height in the hot water supply pipe at that time. In practice, maintaining the highest pressure has the advantage that no additional control is required. When the piston 7-31 reaches the forward end and a predetermined amount of gas is introduced, the valve 7-5 is closed, the pressure in the airtight chamber 4 is released, the mold is opened, and the product is taken out. Further, the valve 7-8 is opened, and an inert gas is introduced into the hot water supply pipe 3 to prevent oxidation of the molten metal. Thereafter, the lance 6-1 is raised, and the next casting is awaited. This progress is shown in FIG.
Is shown in Although the case of introducing the gas at a constant amount is shown, the gas may be introduced in a pattern in which the flow rate is gradually increased so as to keep the speed of returning hot water constant.

FIG. 2 shows an embodiment for a pressure type differential pressure casting.
As shown in FIG. FIG. 7 shows a control device, and FIG. 9 shows a characteristic diagram. Since the operation is almost the same as that of the depressurization type, only the matters unique to the pressurization type will be described. In the decompression type, the decompression after solidification did not directly act on the molten metal in the hot water supply pipe 3, but in the pressurization type, the furnace pressure directly acts. 2 and 4,
A casting machine control panel 9 controls the furnace pressure and the gas introduction device 6 instead of the control panel 7 of the gas introduction device in the case of the reduced pressure type. In FIG. 9, the setting signal of the pressure pattern generation circuit 9-2 is set to the target value during the period from casting to holding, and the valve 7-
The back pressure of the lance 6-1 via the pressure sensor 8 is measured by the pressure sensor 7-9, and the pressure control device 9-1 controls the supply valve 9-3 and the exhaust valve 9
-4 is opened and closed, and the inert gas is introduced into the furnace from the pressurized inert gas source 8 or exhausted to the atmosphere, so that the back pressure follows the set pattern.

Since the molten metal level can be measured from the back pressure of the lance 6-1 as described above, the level of the cast metal can follow the set signal. At this time, the supply pressure in the gas introducing device 6 is set to be equal to or higher than the maximum value of the furnace 1 pressurization. Further, as a result, it is not necessary to perform correction by reducing the amount of molten metal in the furnace 1 at each casting. In the hot water return step, the valves 7-8 are closed. At the same time, the output of the pressure sensor 7-9 is switched to the input of the pressure sensor 9-5, and the internal pressure of the furnace 1 is directly controlled.

Next, the lance 6-1 is lowered, and gas is introduced into the hot water supply pipe 3. The internal pressure of the furnace 1 is reduced in a set pattern, and at the same time, the piston 7-31 of the fixed gas supply device 7-3.
Link the moving speed of As a result, the molten metal in the hot water supply pipe 3 lowers its surface level as the internal pressure of the furnace 1 decreases, and returns to the furnace 1.
The speed of the returning hot water can be controlled by the pressure decreasing speed. At this time, it is desirable that the flow rate of the introduced gas is set so that the gas pressure in the hot water supply pipe 3 is always 1 atm, and the internal pressure of the furnace 1 is reduced at a predetermined speed as a pressure equivalent to the molten metal head inside the hot water supply pipe. That is, in the pressurized type, it is possible to control and return the hot water by the internal pressure of the furnace 1 by introducing gas into the hot water supply pipe.

As in the case of the depressurization type, even if gas is sent to the hot water supply pipe 3 while maintaining the pressurization and the level of the hot water is lowered, the internal pressure of the hot water supply pipe 3 is high when the internal pressure of the furnace 1 is released. Spouting into the inside or gas, spoiling the object of the present invention. Further, in a state in which the pressurization of the furnace 1 is released, there is a possibility that the molten metal will naturally drop due to some leak during the reflow of the molten metal, so that the molten metal cannot be practically used. In this embodiment, the casting is controlled by the back pressure. However, the casting can be performed by the internal pressure in the furnace 1. The inert gas is pressurized in the furnace 1 and the lance 6-1.
For example, argon may be provided in the hot water supply pipe 3 and nitrogen gas may be provided in the furnace 1 separately. FIG. 9 shows a pressure change and a flow rate change in a pressurized system. When the pressure of the furnace 1 is reduced at a constant speed, the flow rate of the introduced gas in the case of hot water reconstitution may be a constant flow rate as shown in FIG.

In both embodiments, the piston type quantitative supply device is used for introducing the gas. However, another type may be used in which the flow rate is measured and the integrated value is used. Further, the lance 6-1 moves up and down, but other moving means such as a horizontal direction may be used. In both cases, it is desirable that the lance 6-1 always flow a gas in order to prevent the lance 6-1 from being closed. Further, since it is always used by being immersed in the molten metal, a ceramic product is preferable to a metal member.

[0018]

According to the differential pressure casting method of claims 1 and 2, since the inert gas is introduced into the hot water supply pipe through the molten metal, the returning hot water can be controlled. It is possible to maintain the reduced pressure, to gradually reduce the applied pressure, and to prevent the natural fall, and to provide a stable differential pressure casting method. Further, since the introduction of the gas is performed by changing the position of the lance, there is no possibility that the gas is mixed during casting and holding. The gas introduction device itself can constantly measure the molten metal level in the furnace from the back pressure, can detect an unexpected blockage or a sudden leak, and can operate stably.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a depressurization type at the start of hot water refining upon completion of casting.

FIG. 2 is a cross-sectional view of a pressurized type at the start of hot water replenishment upon completion of casting.

FIG. 3 is a cross-sectional view showing a situation other than a hot water return step in the case of a reduced pressure type.

FIG. 4 is a cross-sectional view showing a situation other than a hot water return step in the case of a pressure type.

FIG. 5 shows the contents of a control panel of the gas introduction device of FIG.

FIG. 6 is an operation diagram showing operations of a valve and a lance in FIG. 5 for each process.

FIG. 7 shows the contents of the casting machine control panel of FIG. 2;

FIG. 8 is a characteristic diagram showing a change in the degree of pressure reduction of the airtight chamber and a change in the gas flow rate of the lance in the case of the pressure reducing method.

FIG. 9 is a characteristic diagram showing a change in the internal pressure in the airtight chamber and a change in the flow rate of the lance in the case of the pressurized type.

[Explanation of symbols]

 Reference Signs List 1 molten metal container 2 molten metal 3 hot water supply pipe 4 airtight chamber 5 mold 5-3 cavity 6 gas introduction device 7 gas introduction device control panel 8 pressurized inert gas source 9 casting machine control panel

Claims (2)

[Claims] 1. Depressurizing a cavity in a mold, sucking molten metal in a molten metal container into the cavity via a hot water supply pipe, filling the cavity in the mold, holding the product until solidification, and then passing inert gas through the molten metal into the hot water supply pipe. Introduce at a predetermined flow rate,
A reduced-pressure differential pressure casting method comprising the steps of releasing the decompression of the cavity in the mold and opening the mold when a predetermined amount is introduced. 2. An airtight furnace is pressurized and filled with a molten metal into a cavity in a mold via a hot water supply pipe communicating with the cavity in the mold. The molten metal is held until solidification of the product. Thereafter, the pressure in the airtight furnace is reduced at a preset speed. At the same time, a predetermined amount of an inert gas is introduced at a predetermined flow rate at the same time as the time when the pressure in the hermetic furnace reaches the atmospheric pressure by passing the inert gas through the molten metal into the hot water supply pipe, and the pressure in the hermetic furnace is increased. A pressure-type differential pressure casting method characterized in that the mold is opened and the product is taken out after reaching the atmospheric pressure.