JPH10277722A - Differential pressure casting method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fill up molten metal into a cavity at a prescribed initial speed regardless of the pressure in the cavity. SOLUTION: This casting method is provided with a process for adjusting the pressure in the cavity 16 to a first prescribed pressure, the pressure in a molten metal storing vessel 25 to a second prescribed pressure and the pressure in a molten metal reservoir 20r to a third prescribed pressure under condition of closing a molten metal passage 18 with a gate mechanism 19 and thereafter, a process for filling up the molten metal 20 into the cavity 16 and solidifying it by opening the gate mechanism 19. Then, the casting apparatus provided with the sealed molten metal storing vessel 25 in which the differential pressure between the second prescribed pressure and the third prescribed pressure is set so as to raise the surface of molten metal 26 having the prescribed quantity or more in the molten metal reservoir 20r, the cavity 16 filled up with the molten metal 26 therein, the molten metal passage 18 for communicating the molten metal storing vessel 25 and the cavity 16, the gate mechanism 19 for opening/closing this passage and the molten metal reservoir 20r branched from the molten metal passage 18 in the molten metal storing vessel 25 side the gate mechanism and extended to the higher position than the cavity 16, is used to execute the casting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method and apparatus for filling a cavity with molten metal in a hot water storage tank and solidifying the same.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Application Laid-Open No.
No. 7519 is known. This differential pressure casting apparatus pressurizes the surface of the molten metal in the hot water tank as shown in FIG. 4 and sucks the molten metal in the hot water tank into the molten metal passage, and casts the molten metal in the molten metal passage as shown in FIG. In some cases, the pressure inside the storage tank is sucked into the molten metal passage by reducing the pressure. The apparatus shown in FIG. 4 has a mold 30 including an upper mold 32 and a lower mold 34, and a cavity 36 is formed in the mold 30. The cavity 36 is connected to a vacuum pump (not shown) so that the inside of the cavity 36 can be depressurized. The cavity 36 communicates with a hot water storage tank 46 for storing the molten metal 48 via a molten metal passage 38.
A gate piston 40 is provided in the molten metal passage 38 so that the molten metal passage 38 can be opened and closed.
The gate piston 40 has a molten metal reservoir 40r for storing the molten metal 48 above the gate 38a, and the upper end thereof is open to the atmosphere. The hot water storage tank 46
Is installed in a melting furnace 45 closed by a furnace wall 44. The melting furnace 45 is connected to a pressurized air supply device (not shown) so that the surface of the molten metal 48 in the hot water tank 46 can be pressurized. To perform casting in such a device,
First, with the gate piston 40 closed, the melting furnace 45 is closed.
Pressurized air is supplied to the inside, and the surface of the molten metal 48 in the hot water storage tank 46 is pressurized. When the inside of the melting furnace 45 is pressurized, the molten metal 48 rises in the molten metal passage 38 by the pressure. When the surface of the molten metal sucked into the molten metal passage 38 rises to a predetermined height (a position at a height h from the gate 38 a), the melting furnace 4
The pressurization in 5 ends. Simultaneously with the pressurization in the melting furnace 45,
The pressure in the cavity 36 is set to a predetermined value by a vacuum pump. In this state, by opening the gate piston 40, the molten metal in the molten metal passage 38 is filled into the cavity 36 and cast. 5 is different from the apparatus shown in FIG. 5 in that the hot water storage tank 46 is opened to the atmosphere and a vacuum pump (not shown) is connected to an exhaust port 40a provided in the gate piston 40. Therefore, in order to perform casting with the apparatus shown in FIG. 5, the pressure inside the molten metal reservoir 40r is reduced by a vacuum pump connected to the exhaust port 40a, and the molten metal is sucked into the molten metal passage 38. After the inside of the cavity 36 is set to a predetermined pressure, the molten metal sucked into the molten metal passage 38 by opening the gate piston 40 is filled into the cavity 36 and cast.

[0003]

In such a casting apparatus, in any case, before the gate piston 40 is opened, the following relational expression is established from the balance of the forces. Here, the pressure P _f in the hot water storage tank, the pressure P _r in the molten metal reservoir,
The height h of the molten metal from the gate 38a and the hot water storage tank 46
Let H be the height from the molten metal surface to the gate. The gravity acceleration is g, and the density of the molten metal is ρ.

[0004] P_f= P_r+ Ρg (H + h) (1) This relationship is graphically shown in FIG. In FIG. 3, the pressure is plotted on the vertical axis.
And the force balance in the device shown in FIGS. 4 and 5
And the case according to the present invention described below
I have. As shown in FIG. 3, the apparatus shown in FIG.
Pressure in the reservoir P _rBecomes the atmospheric pressure and the pressure P in the hot water tank
_fIs the pressure P in the molten metal reservoir_rPressure due to the weight of the molten metal
ρg (H + h) is applied. Shown in FIG.
In the device, the pressure P in the hot water tank_fIs at atmospheric pressure,
Pressure P in molten metal reservoir_rIs the pressure P in the hot water tank_fDissolving from
The pressure is obtained by subtracting the pressure ρg (H + h) due to the weight of the hot water.
ing. In such a casting apparatus, the cavity 36
The initial speed v of filling the molten metal into the inside is determined by the inlet of the gate 38a and the cap.
It is determined by the pressure difference between the vitities 36. Entrance of the gate 38a
Is the pressure P in the molten metal reservoir._rDue to the weight of the molten metal
Pressure (P)_r+ Ρgh). Obedience
The pressure in the cavity is P_cThen, the gate 38
The pressure difference between the inlet a and the cavity 36 is as follows.
You.

[0005] A P _r + ρgh over P _c ··· (2) this pressure difference, the case of the apparatus of FIG. 4 and FIG. 5 to FIG. 3, respectively as differential pressure. In the apparatus shown in FIG. 4, the pressure P _r in the molten metal reservoir becomes the atmospheric pressure. Here, the height h of the molten metal from the gate 38a and the height H from the surface of the molten metal in the hot water storage tank 46 to the gate are values determined by the apparatus. Further, the pressure _Pc in the cavity is maintained at a high degree of vacuum from the viewpoint of reducing the amount of air entrained in the molten metal filled in the cavity. Therefore, the initial filling speed of the molten metal into the cavity was a value determined by the structure of the apparatus. Also in the apparatus shown in FIG. 5, the pressure P _f in the hot water tank is in the atmospheric pressure, the structural determined pressure of the pressure P _r is also devices in the molten metal reservoir. Here, the gate 38a
The height h of the molten metal from the melt, the height H from the surface of the molten metal in the hot water storage tank 46 to the gate, and the pressure _Pc in the cavity are the same as those in the above-described apparatus of FIG. It is a value determined by the above. Therefore, also in the apparatus shown in FIG. 5, the initial filling speed of the molten metal into the cavity was a value determined by the structure of the apparatus. Therefore, in the conventional apparatus, when the initial filling speed of the molten metal is too slow, there is a problem that the flowability of the molten metal into the cavity is deteriorated, and when the initial filling speed of the molten metal is too fast, There is a problem that the surface layer of the molten metal filled in the cavity is broken, and the molten air entrains residual air in the cavity.

[0006]

Accordingly, the above-mentioned problems are solved by a casting method and apparatus having the following features. That is, the invention according to claim 1 includes a sealed hot water storage tank, a cavity filled with molten metal in the hot water storage tank,
A molten metal passage communicating the molten metal storage tank and the cavity, a gate mechanism for opening and closing the molten metal passage, and branching from the molten metal passage closer to the molten metal storage tank than the gate mechanism and extending to a position higher than the cavity. In a casting method performed using a casting apparatus having a molten metal reservoir,
With the molten metal passage closed by the gate mechanism, the pressure in the cavity is set to a first predetermined pressure, the pressure in the hot water storage tank is set to a second predetermined pressure, and the pressure in the molten metal reservoir is set to a third predetermined pressure. A step of adjusting and then a step of filling and solidifying the molten metal into the cavity by opening the gate mechanism, wherein the second predetermined pressure and the third predetermined pressure are a predetermined amount in the molten metal reservoir. It is characterized in that the pressure difference is set so that the molten metal rises. According to the above method, the pressure in the cavity, the pressure in the hot water tank, and the pressure in the molten metal reservoir are set to predetermined values with the gate mechanism closed. Therefore, since the pressure difference between the inside of the cavity and the entrance of the gate section can be controlled to an arbitrary value,
The molten metal is sucked and filled into the cavity at a predetermined initial speed. That is, in the present invention, the pressure P _f in the hot water tank and the second predetermined pressure, the pressure P _r in the molten metal reservoir and a third predetermined pressure. Here, since the second predetermined pressure and the third predetermined pressure are set to a pressure difference at which a predetermined amount or more of the molten metal rises in the molten metal reservoir, the molten metal in the hot water storage tank is placed in the molten metal passage. A predetermined amount is sucked and the surface level of the molten metal becomes h. Thus, by controlling the pressure P _r of the pressure P _f and the melt reservoir remains hot water storage tank to maintain a melt-surface height h of the molten metal, to differential pressure (P _r + ρgh over P _c) and any value Can be. Therefore, the initial filling speed of the molten metal in the cavity can be controlled. For example, if the poor water around property, as in the invention sample A shown in FIG. 3, the pressure P _f in the hot water tank and the second predetermined pressure above atmospheric pressure, the pressure P _r in the molten metal reservoir large A third predetermined pressure equal to or higher than the atmospheric pressure. Therefore, differential pressure (P _r + ρgh over P _c) can be increased as compared with the conventional device shown in FIG. 4, it may be filled with molten metal into the cavity instantaneously faster the melt filling initial velocity. Further, when it is desired to prevent air from being entrained in the molten metal, as shown in Example B of the present invention shown in FIG.
The _f and below the second predetermined sub-atmospheric pressure, and a third predetermined pressure the pressure P _r in the molten metal reservoir below atmospheric pressure. Therefore, differential pressure (P _r + ρgh over P _c) to indicate can be reduced as compared with the conventional device FIG. 5, a slower melt filling initial velocity can be slowly filled with the molten metal into the cavity. Here, the amount of the molten metal sucked into the molten metal reservoir is set so that the amount of the molten metal in the molten metal passage to the lowest gate portion is filled (h ≧ 0). Preferably, it is desirable to suck the molten metal into the molten metal reservoir at a position higher than the sprue and at a level that can store the molten metal having a volume equal to or larger than the cavity. If the initial filling speed of the molten metal into the cavity is high, the air on the upper surface of the molten metal sucked into the molten metal reservoir is sucked into the cavity.

According to a second aspect of the present invention, in the casting method of the first aspect, the first predetermined pressure, the second predetermined pressure, and the third predetermined pressure are all set to an atmospheric pressure or less. It is characterized by the following. According to the above method, the pressure in the sprue inlet and the inside of the cavity is set so that the pressure in the hot water tank is set to the second predetermined pressure equal to or lower than the atmospheric pressure and the pressure in the molten metal reservoir is set to the third predetermined pressure equal to or lower than the atmospheric pressure. The difference can be reduced, and the initial filling speed of the molten metal can be reduced as compared with the conventional apparatus. That is, this corresponds to the case of the invention sample B shown in FIG.

According to a third aspect of the present invention, in the casting method of the first aspect, the first predetermined pressure is set to a high degree of vacuum. According to the above method, since the first predetermined pressure is set to a high degree of vacuum, the amount of residual air in the cavity can be reduced, and the amount of air remaining in the cavity into the molten metal can be reduced. .

According to a fourth aspect of the present invention, in the casting method of the first aspect, the initial speed of filling the molten metal into the cavity is such that the surface layer of the molten metal flowing into the cavity is not broken. The first predetermined pressure, the second predetermined pressure, and the third predetermined pressure are set. According to the above method, the first predetermined pressure, the second predetermined pressure, and the third predetermined pressure are set so that the surface layer of the molten metal flowing into the cavity is not broken. Therefore, it is possible to prevent the residual air in the cavity from being caught in the molten metal flowing into the cavity. Here, the speed at which the surface layer of the molten metal flowing into the cavity is not destroyed specifically means that the Reynolds number is 2
It refers to the speed at which the value is lower than 0000.

According to a fifth aspect of the present invention, in the casting method of the first aspect, the step of adjusting the pressure in the hot water storage tank to a second predetermined pressure and adjusting the pressure in the molten metal reservoir to a third predetermined pressure. The difference between the pressure in the hot water tank and the pressure in the molten metal reservoir so that the surface layer of the molten metal sucked in the molten metal passage is not broken by the pressure difference in the hot water tank and the pressure in the molten metal reservoir. The temporal change rate of the pressure difference is controlled. According to the above method, the rate of change in time between the pressure in the hot water tank and the pressure difference in the molten metal reservoir is controlled, so that the speed of the molten metal sucked into the molten metal passage can be controlled. Here, since the speed of the molten metal is controlled so that the surface layer of the molten metal sucked into the molten metal passage is not destroyed, it is possible to prevent entrainment of air in the molten metal passage into the molten metal sucked into the molten metal passage. Can be. Here, the speed at which the surface layer of the molten metal sucked into the molten metal passage is not destroyed means the speed at which the Reynolds number is lower than 20,000 as described above.

According to a sixth aspect of the present invention, in the casting method according to the second aspect, the step of adjusting the pressure in the hot water storage tank to a second predetermined pressure and adjusting the pressure in the molten metal reservoir to a third predetermined pressure. Are performed at the same time, and the pressure reduction speeds of both are controlled to be the same.
After reaching a predetermined pressure, the pressure in the molten metal reservoir is further reduced to suck the molten metal in the storage tank into the molten metal passage. According to the above method, the pressure in the hot water storage tank and the pressure in the molten metal reservoir are reduced at the same decompression rate. Therefore, while the pressure in the hot water tank is reduced to the second predetermined pressure, the molten metal in the hot water tank is not sucked into the molten metal passage. Therefore, before the molten metal in the hot water storage tank is sucked into the molten metal passage, the inside of the molten metal passage is in a depressurized state, so that the amount of entrained air remaining in the molten metal passage into the molten metal sucked into the molten metal passage is reduced. Less.

The invention according to claim 7 provides a sealed hot water storage tank, a cavity filled with the molten metal in the hot water storage tank, a molten metal passage communicating the hot water storage tank with the cavity, and a molten metal passage. In a casting apparatus having a gate mechanism that opens and closes and a molten metal reservoir that branches from the molten metal passage and extends to a position higher than a cavity on a side of the molten metal storage tank closer to the gate mechanism, the pressure in the hot water storage tank is controlled. It is characterized by comprising a hot water tank pressure control means, a pressure control means for controlling the pressure in the cavity, and a pressure control means in the melt reservoir for controlling the pressure in the melt reservoir. According to the above-mentioned apparatus, since means for controlling the pressure in the hot water storage tank, the pressure in the cavity, and the pressure in the molten metal reservoir are provided, it is possible to control the initial speed of filling the molten metal into the cavity.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a drawing showing a configuration of a casting apparatus according to one embodiment of the present invention. This casting apparatus has a mold 10 composed of an upper mold 12 and a lower mold 14,
A cavity 16 is formed in the mold 10. Also,
The upper mold 12 is provided with a chamber 12d that communicates with the cavity 16 via the gap 13. An exhaust port 12b is provided in the chamber 12d, and is connected to a vacuum pump (not shown) via a pipe 12c and a control valve 29c. By operating this vacuum pump, the air in the chamber 12d and the cavity 16 is sucked, and the inside of the cavity 16 can be set to a predetermined pressure (degree of vacuum). The vacuum state in the cavity 16 is measured by a pressure sensor (not shown) provided in the chamber 12d, and a signal obtained by the pressure sensor is sent to the controller 28 via the actual vacuum monitor 27. The controller 28 opens and closes the control valve 29c based on the signal of the pressure sensor, and can maintain the inside of the cavity 16 at a predetermined degree of vacuum. That is, in the present embodiment,
The pipe 12c, the pressure sensor installed in the chamber 12d, the vacuum pump connected to the pipe 12c, the controller 28, and the control valve 29c function as the pressure control means in the cavity. The upper mold 12 has the cavity 1
A pressurizing pin 22 is provided to press the molten metal in the cavity 16 when the molten metal is filled and solidified in 6. The pressure pin 22 is driven in a vertical direction by a driving device (not shown).

A cavity 16 formed in the mold 10
Is connected through a molten metal passage 18 to a hot water storage tank 25 that melts the casting metal and stores it as a molten metal 26. This hot water storage tank 25 can melt the casting metal by a heating device (not shown) and maintain the molten state. The hot water storage tank 25 is installed in a melting furnace 23 composed of a lower mold base 15 and a furnace wall 24 attached to the lower mold base 15. An exhaust port 24a is provided in the furnace wall 24, and the exhaust port 24a has a pipe 24b and a control valve 29f.
Is connected to a vacuum pump (not shown).
This is because, in the present embodiment, it is necessary to reduce the initial speed of filling the molten metal into the cavity 16. Conversely, if the initial speed of filling the molten metal is to be increased, it is connected to the pressurized air supply device. That is, the present embodiment corresponds to the present invention example B shown in FIG.
Is equivalent to The degree of vacuum of the melting furnace 23 is measured by a pressure sensor (not shown) installed in the melting furnace 23. The signal obtained by the sensor is sent to the controller 28 via the actual vacuum monitor 27. Control controller 28
Can open and close the control valve 29f based on the signal of the pressure sensor, and can set the pressure in the hot water storage layer 25 (the pressure in the melting furnace 23) to a predetermined pressure. That is, in the present embodiment,
Pipe 24b, pressure sensor installed in melting furnace 23, vacuum pump connected to pipe 24b, controller 2
8, and the control valve 29f function as pressure control means in the hot water tank.

The melt connecting the cavity 16 and the hot water tank 25
The hot water passage 18 is provided with a hot water port 18 a and a molten hole formed in the lower mold 14.
Stoke 1 attached to hot water passage 18b and lower mold 14
8c. The molten metal passage 18 b communicates with the cavity 16.
A sluice portion 18a through which a molten metal, which will be described later, extends further upward.
It branches to hot water reservoir 20r. Beyond Stoke 18c
The end is immersed in the molten metal 26 of the hot water storage tank 25. Gate
A shut pin 21 is provided in the portion 18a, and the cavity
When the molten metal is filled in the
The cavity 16 and the melt passage 18b.
ing. At the boundary between the gate section 18a and the molten metal passage 18b,
A gate mechanism 19 is provided, and the cavity 16 and the
The molten metal passage 18 communicating with the hot water storage tank 25 can be opened and closed.
Has become. The gate mechanism 19 includes the gate piston 2
0 and a diagram in which the gate piston 20 is displaced in the axial direction.
It comprises a drive mechanism not shown. Of this gate piston 20
Details are shown in FIG. Gate piston 20 has a cylindrical side
The upper mold 12 includes a wall 20a and an upper plate 20b.
Slidably inserted through the through hole 12a. Gate
The upper plate 20b of the ston 20 is connected to a drive mechanism not shown.
Is done. With this drive mechanism, the gate piston 20 moves up and down.
To connect the cavity 16 and the hot water storage tank 25.
The molten metal passage 18 can be opened and closed at the entrance of the gate section 18a.
Swelling. That is, the through hole 1 provided in the upper die 12
2a is the diameter of the molten metal passage 18b formed in the lower mold 14.
Larger by the thickness of the side wall 20a of the gate piston 20
The gate piston is made and inserted into the through hole 12a.
The lower mold 20 is brought into contact with the lower mold 14 so that the lower mold 20
14 and the melt passage 18 b provided in the cavity 16.
Is shut off at the entrance of the gate 18a. Gate gate
The inner space of the stone 20 is located higher than the spout 18a.
Molten metal reservoir that stores more than the volume of cavity 16
Functions as the server 20r. The upper plate 20b has an exhaust
A port 20c is provided, and the exhaust port 20c is connected to a pipe 20d and a pipe 20d.
And a vacuum pump (not shown) through the control valve 29r.
Have been. The degree of vacuum in the molten metal reservoir 20r depends on the gate
The pressure is measured by a pressure sensor (not shown)
Is determined. The signal from the pressure sensor is sent to the actual vacuum monitor 27.
Sent to the controller 28 via the Control control
In the controller 28, the control valve is controlled based on the signal of the pressure sensor.
29r is opened and closed, and the pressure inside the molten metal reservoir 20r is adjusted.
Can be a fixed value. That is, in the present embodiment, the distribution
A pressure sensor installed in the pipe 20d and the gate piston 20
Vacuum pump connected to pipe 20d, control controller
Roller 28 and control valve 29r control the pressure in the molten metal reservoir.
Functions as a means. In this embodiment, the pipe 20d
Is connected to a vacuum pump, but the initial speed of filling the molten metal is increased.
For this purpose, a pressurized air supply device is connected to the exhaust port 24a of the furnace wall 24.
If it continues, depending on the pressure value in the hot water tank 25,
A pressurized air supply device may be connected to 20d. Immediately
That is, as shown in Example A of the present invention shown in FIG.
Pressure P _fIs set high, the melt reservoir 20r
Pressure P_rMay have to be above atmospheric pressure
That's why.

Next, the operation of the casting apparatus when casting is performed in such a casting apparatus will be described. First, with the gate piston 20 closed, the control valves 29f, 29r
To operate the vacuum pumps connected to the pipes 20d and 24b to start reducing the pressure in the hot water storage tank 25 and the molten metal reservoir 20r at the same pressure reduction rate. Since the pressure in the hot water storage tank 25 and the pressure in the molten metal reservoir 20r are reduced while being kept the same, the hot water storage tank 2 installed in the melting furnace 23 is reduced.
5 is depressurized without being sucked into the molten metal passage 18. Hot water storage tank 25 and molten metal reservoir 2
The pressure within 0r is measured by pressure sensors provided in the melting furnace 23 and the gate piston 20, respectively. When the pressure in the hot water tank 25 reaches a predetermined pressure, the control valve 29f is closed by a signal from the controller 28, and the pressure reduction in the hot water tank 25 is completed. Here, the pressure in hot water storage tank 25 is set in the following procedure. That is, the pressure difference between the inlet and the cavity of the sprue 18a (P _r + ρgh over P _c)
Is (P _f -P _c -ρg) from the relationship of the above-mentioned equation (1).
H). Accordingly, assuming that there is no flow loss at the gate piston 20, the initial velocity v of filling the molten metal into the cavity is expressed by the following equation.

V = (2 × (P _f −P _c ) / ρ−2 gH) ^0.5 (3) Here, the pressure P _f in the hot water storage tank 25 and the molten metal reservoir 20 r
Pressure P _r , pressure P _c inside cavity 16, gate 1
The molten metal surface height h from 8a, the height from the molten metal surface of the hot water storage tank 25 to the sprue portion is H, the weight acceleration g, and the density of the molten metal are ρ. Actually, assuming that the flow rate loss at the gate piston 20 is C and the velocity coefficient at the gate piston is C, the following equation is used.

V = C × (2 × (P _f −P _c ) / ρ−2gH) ^0.5 (4) Here, the velocity coefficient C of the gate piston 20 is determined by the shapes of the gate piston 20 and the gate section 18a. This is a coefficient determined by the above, etc., and is separately obtained through experiments or the like. The flow velocity v of the molten metal flowing into the cavity 16 must be set at a speed that does not destroy the surface layer of the molten metal. This is because the molten metal flowing into the cavity 16 does not entrain the residual air in the cavity 16. Specifically, the Reynolds number of the molten metal is 20
It may be determined appropriately within a range not exceeding 000. Also, the flow rate of the molten metal should be as small as 20
It is preferable to determine in the range close to 000. Therefore,
The flow velocity v of the molten metal and the pressure P _c in the cavity 16 are determined,
Based on these values, the pressure P _f in the hot water tank 25 is determined from the above-described equation (4) (in this example, the pressure P _f in the hot water tank 25 is determined).
_f is reduced from 760 Torr to 231 Torr, for example).

After the control valve 29f is closed and the pressure in the hot water storage tank 25 is reduced, the pressure in the molten metal reservoir 20r is reduced. Accordingly, the pressure P _r in the molten metal reservoir 20r is lower than the pressure P _f in the hot water tank 25, the molten metal 26 in the hot water tank 25 is sucked into the melt passage 18. in this way,
Since the molten metal 26 in the storage tank 25 is sucked after the pressure in the molten metal reservoir 20r (the molten metal passage 18) is reduced to some extent, the amount of residual air in the molten metal passage 18 that is drawn into the molten metal in the molten metal passage 18 is reduced. can do. Also,
The suction speed of the molten metal is proportional to the pressure reduction speed in the molten metal reservoir 20r. If the surface layer of the sucked molten metal is broken even though the inside of the molten metal passage 18 is decompressed to some extent, residual air in the molten metal passage 18 may be caught in the molten metal and cause casting defects. Therefore, it is preferable to set the decompression speed in the molten metal reservoir 20r within a range where the surface layer of the molten metal to be sucked is not broken. Specifically, if the rising speed of the molten metal and v _t, in time dt melt v _t dt only the surface of the molten metal is that it has increased. d
Assuming that the pressure in the molten metal reservoir 20r decreases by dp within the time t, the following equation is established by the balance of the forces.

Dp = −ρgv _t dt (5) Accordingly, if the rising speed v _t of the molten metal is determined, the pressure reduction speed in the molten metal reservoir 20r is determined. Melt rise speed v _t
May be appropriately determined within a range in which the surface layer of the molten metal is not broken, that is, the Reynolds number does not exceed 20,000. When the pressure in the molten metal reservoir 20r reaches a predetermined pressure, the controller 28 closes the control valve 29r based on the signal of the pressure sensor installed on the gate piston 20, and the pressure reduction in the molten metal reservoir 20r is completed. Here, the pressure in the molten metal reservoir 20r is, as shown in FIG.
The height of the molten metal is set to a predetermined height h from a. Specifically, it is preferable to determine the height h so that the surface of the molten metal is higher than the spout 18a and the volume of the molten metal stored in the molten metal reservoir 20r is equal to or larger than the volume of the cavity 16. . This is because when the filling rate of the molten metal into the cavity 16 is high, the molten metal reservoir 20r
This is because air or the like on the upper surface of the molten metal stored in the cavity 16 is sucked into the cavity 16. Therefore, if the molten metal surface height h is determined, the pressure in the molten metal reservoir 20r is determined by the following equation (in the present example, the pressure is reduced to, for example, 1 Torr). Here, the pressure P _f in the hot water storage tank, the pressure P _r in the molten metal reservoir, the height h of the molten metal from the spout 18a, and the height from the surface of the molten metal in the hot water storage tank 25 to the spout are H. . The weight acceleration is g, and the density of the molten metal is ρ.

P _r = P _f -ρg (H + h) (6) In the present embodiment, the hot water storage tank 25 and the molten metal reservoir 20
After the pressure in the hot-water storage tank 25 reached a predetermined pressure, the pressure in the molten metal reservoir 20r was further reduced. However, if the speed of the molten metal rising in the molten metal passage 18 does not exceed the Reynolds number of 20000, the decompression speed in the molten metal reservoir 20r is set to be greater than the decompression speed in the hot water storage tank 25, and The pressure inside the hot water storage tank 25 may be reduced while sucking.

Simultaneously with the reduced pressure in the hot water storage tank 25 and the reduced pressure in the molten metal reservoir 20r, the inside of the cavity 16 is reduced to a predetermined pressure (degree of vacuum). When the pressure in the cavity 16 reaches a predetermined pressure, the controller 28 controls the control valve 2 based on the signal of the pressure sensor installed in the chamber 12d.
9c is closed, and the pressure reduction in the cavity 16 is completed. The pressure in the cavity 16 is set to a high vacuum level (in this example, reduced to 1 Torr, for example) in order to reduce the amount of air remaining in the cavity 16 into the molten metal. After the decompression of each part is completed, the gate piston 20 rises and the molten metal passage 18 is opened. Therefore, the molten metal in the molten metal passage 18 is sucked and filled into the cavity 16 by the pressure difference between the inlet of the gate section 18a and the cavity 16 (in this example, the pressure in the molten metal reservoir 20r and the pressure in the cavity 16). Are the same, the differential pressure between the inlet of the gate 18a and the cavity 16 is vacuum gravity casting with only the head pressure ρgh of the molten metal.) When the cavity 16 is filled with the molten metal, the shut pin 21 is driven to shut off the cavity 16 and the molten metal passage 18b. In accordance with the progress of solidification of the molten metal in the cavity 16, pressure is applied by the pressure pin 22 to complete casting.

As described above, in the present embodiment, by setting the pressure in the hot water storage tank 25 and the pressure in the molten metal reservoir 20r to predetermined values based on the pressure in the cavity 16, a desired pressure (vacuum degree) can be obtained. The cavity 16) can be filled with the molten metal at a predetermined initial speed. Accordingly, the initial speed of filling the molten metal can be increased within a range in which the surface layer of the molten metal filled in the cavity 16 is not destroyed, and it is possible to prevent the entrapment of the residual air into the molten metal and to ensure the flowability of the molten metal. Further, since the pressure in the hot water storage tank 25 and the molten metal reservoir 20r is reduced every casting, hydrogen in the molten metal in the hot water storage tank 25 and hydrogen in the molten metal sucked in the molten metal passage 18b are degassed. Therefore, the hydrogen gas level in the molten metal can be kept low, and a sound cast product can be obtained. Also,
Since the pressure in the hot water storage tank 25 and the pressure in the molten metal reservoir 20r are reduced at the same decompression speed, when the molten metal rises in the molten metal passage 18, the pressure in the molten metal passage 18 is already reduced. Therefore, the molten metal passage 1 to the molten metal sucked into the molten metal passage 18
8 can reduce the amount of entrained residual air.
Furthermore, since the depressurizing speed in the molten metal reservoir 20r is controlled so that the rising speed of the molten metal does not destroy the surface layer of the molten metal, air entrapment in the molten metal can be prevented.

According to the above casting method, 200 mm × 100
A plate-shaped test piece having a thickness of 10 mm and a thickness of 10 mm was cast. As the casting metal, aluminum alloy (AC according to JIS standard)
4CH) was used. The melt temperature was set at 750 degrees. The mold temperature of the upper mold 12 and the lower mold 14 was 150 ° C., and a graphite release material was applied to the mold surface. First, the pressures in the hot water storage tank 25 and the molten metal reservoir 20r are increased at the same decompression speed (20
(Torr / Sec) to 205 Torr. After a while, the inside of the molten metal reservoir 20r is further filled with 10.5 Torr.
r to a predetermined level (h = 20c
m). Hot water tank 25 and molten metal reservoir 20
r, the pressure in the cavity 16 is reduced by 0.5
The pressure was reduced to Torr. In this state, the gate piston is opened, and the molten metal in the molten metal passage 18 is filled with the molten metal at an initial speed of about 2 m / s.
To fill the cavity 16. The molded product was of high quality without any defects due to gas bubbles inside.

[0025]

As described above, in the casting method according to the first aspect, the pressure in the cavity, the pressure in the hot water storage tank, and the pressure in the molten metal reservoir are each set to a predetermined pressure. The initial melt filling speed can be controlled.

In the casting method according to the second aspect, the pressure in the hot water tank, the pressure in the cavity, and the pressure in the molten metal reservoir are set to be equal to or lower than the atmospheric pressure. .

Further, in the casting method according to the third aspect, since the inside of the cavity is made to have a high degree of vacuum, the amount of entrained air remaining in the cavity into the molten metal can be reduced.

In the casting method according to the fourth aspect, the pressure in the cavity, the pressure in the hot water storage tank, and the pressure in the molten metal reservoir are set such that the initial speed of filling the molten metal is a speed at which the surface layer of the molten metal is not destroyed. As a result, the initial filling speed of the molten metal into the cavity can be kept low, and entrainment of the residual air in the cavity into the molten metal filled in the cavity can be prevented.

Further, in the casting method according to the fifth aspect, the speed of the molten metal sucked into the molten metal passage is set to a speed at which the surface layer of the molten metal is not destroyed. Entrapment of residual air in the interior can be prevented.

In the casting method according to the sixth aspect, the molten metal in the molten metal passage is depressurized before the molten metal in the molten metal storage tank is sucked into the molten metal passage. Can be reduced in the amount of residual air entrained in the melt passage.

In the casting apparatus according to the present invention, since means for controlling the pressure in the hot water storage tank, the pressure in the cavity, and the pressure in the molten metal reservoir are provided, the pressure in the cavity is not changed. The initial speed of filling the cavity with the molten metal can be controlled.

[Brief description of the drawings]

FIG. 1 is a drawing showing a configuration of a casting apparatus according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a main part of a casting apparatus according to one embodiment of the present invention.

FIG. 3 is a graph showing the relationship between each pressure in the apparatus according to the present invention and the conventional apparatus in a graph.

FIG. 4 is a drawing showing a configuration of a conventional casting apparatus.

FIG. 5 is a view showing a configuration of a conventional casting apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Mold 16 ... Cavity 18 ... Melt passage 20 ... Gate piston 23 ... Melting furnace 25 ... Hot water storage tank 27 ... Actual vacuum degree monitor 28 ... Control controller

Claims (7)

[Claims] 1. A sealed hot water storage tank, a cavity filled with the molten metal in the hot water storage tank, a molten metal passage communicating the hot water storage tank with the cavity, a gate mechanism for opening and closing the molten metal passage, and a gate thereof. In a casting method using a casting apparatus having a molten metal reservoir that is branched from the molten metal passage and extends to a position higher than the cavity at a position closer to the molten metal storage tank than a mechanism, the molten metal passage is closed by the gate mechanism. Adjusting the pressure in the cavity to a first predetermined pressure, the pressure in the hot water tank to a second predetermined pressure, and the pressure in the molten metal reservoir to a third predetermined pressure in the state; A step of filling the cavity with the molten metal and solidifying the molten metal, and wherein the second predetermined pressure and the third predetermined pressure are equal to or less than a predetermined amount in the molten metal reservoir. A casting method, wherein a pressure difference at which the upper molten metal rises is set. 2. The casting method according to claim 1, wherein the first predetermined pressure, the second predetermined pressure, and the third predetermined pressure are all set to an atmospheric pressure or less. 3. The casting method according to claim 1, wherein the first predetermined pressure is set to a high degree of vacuum. 4. The casting method according to claim 1, wherein the first predetermined pressure and the second predetermined pressure are such that an initial speed of filling the molten metal into the cavity is a speed at which a surface layer of the molten metal flowing into the cavity is not broken. 2. A casting method, wherein two predetermined pressures and the third predetermined pressure are set. 5. The casting method according to claim 1, wherein the step of adjusting the pressure in the hot water tank to a second predetermined pressure and adjusting the pressure in the molten metal reservoir to a third predetermined pressure comprises: The time change rate of the pressure difference between the pressure in the hot water storage tank and the pressure in the molten metal reservoir so that the surface layer of the molten metal sucked into the molten metal passage is not destroyed by the pressure difference in the molten metal reservoir and the pressure in the molten metal reservoir. A casting method characterized by being controlled. 6. The casting method according to claim 2, wherein the steps of adjusting the pressure in the hot water tank to a second predetermined pressure and adjusting the pressure in the molten metal reservoir to a third predetermined pressure are performed simultaneously, and After the pressure in the hot water storage tank reaches the second predetermined pressure, the pressure in the hot water storage tank is further reduced, and the molten metal in the hot water storage tank is further reduced by controlling the pressure in the hot water storage tank to the second predetermined pressure. A casting method characterized by sucking into a molten metal passage. 7. A sealed hot water storage tank, a cavity filled with the molten metal in the hot water storage tank, a molten metal passage communicating the hot water storage tank with the cavity, a gate mechanism for opening and closing the molten metal passage, and a gate thereof. In a casting apparatus having a molten metal reservoir that is branched from the molten metal passage and extends to a position higher than a cavity on a side of the molten metal tank than a mechanism, a pressure control unit in the molten metal tank that controls a pressure in the molten metal tank, A differential pressure casting apparatus comprising: an in-cavity pressure control means for controlling the pressure in the cavity; and a molten metal reservoir pressure control means for controlling the pressure in the molten metal reservoir.