JPH0337461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a degassing device for a mold used in a molding machine such as a die casting machine.

Conventionally, die casting has been widely used as a method for manufacturing precision products in large quantities, but there are cases where die casting is not suitable for products where the integrity of the product without porosity is important.

The reason for this is that since the cavity is filled with molten metal at high speed and high pressure, the gas in the cavity may not be able to escape sufficiently and may mix with the molten metal and remain in the product as cavities.

In order to eliminate these inconveniences, the applicant's company has developed a technology that allows a large amount of gas to be reliably and easily removed without being restricted by cast products or molds, thereby eliminating gas entrainment and producing sound die-cast products. We have developed a gas venting device for molds that allows this.

This device performs injection with the discharge path leading from the mold cavity to the outside of the mold opened by the action of a valve, and when the gas with a small mass in the cavity has been exhausted through the gas discharge path, By applying the inertial force of the large mass of the molten material to be injected that has advanced from inside the cavity directly to the valve, the valve is reliably and quickly moved and closed, directly cutting off the gas discharge path and removing this gas. It is possible to prevent the melt to be injected from flowing out from the discharge path, and to ensure that gas in the mold can be vented easily during injection.

This degassing device for molds has a spool with a slidably installed valve inside that is movable in the sliding direction of the valve using a cylinder. A stopper mechanism is provided to stop the retreat of the spool and open the valve, and a member is provided at the rear end of the spool that acts to stop only the valve from retreating by the action of the stopper mechanism. Therefore, the height of the degassing device itself has become high and its structure has become complicated.

Note that the mold is cold at the start of injection molding, and it would be inconvenient if the method of injection molding, in which injection molding is performed at a low speed at the initial stage and then at a high speed during normal operation, is applied as is.

That is, if the mold is cold, the molten metal will solidify before reaching the corners of the mold cavity, making it impossible to obtain a perfect molded product. Therefore, usually several shots are injected at low speed to warm up the mold and then normal injection molding is performed.

However, if the valve was operated only at low speed at the start of operation, the inertia of the molten metal would be weak, so the valve would not close and there was a risk that the molten metal would enter the valve. This means that
This phenomenon can also occur when injection molding is performed using only low-speed injection other than at the start of operation.

If molten metal enters the valve, it will solidify there and the degassing device will not be able to perform its function.The degassing device will have to be removed and repaired or replaced, during which time the operation will have to be stopped. , the operational efficiency will decrease.

Further, when the mold is opened, the entire spool is raised, and the valve is stopped from retracting while the spool is retracting, and the valve is opened by a stopper mechanism, and when the mold is clamped, the valve is lowered to a predetermined position with the valve open. However, when the cylinder that lowers the spool is started, hydraulic oil pressure suddenly acts on it, causing a shock that exceeds the holding capacity of the holding mechanism that keeps the valve open, causing the valve to close. Sometimes. If this happens, the device loses its degassing function, and the gas in the cavity cannot escape and remains as bubbles in the product, creating what is called a cavity.

The present invention was made in order to eliminate the above-mentioned conventional drawbacks, and the inertial force of molten metal is When the valve is small, the valve can be closed in advance by remote control to protect the valve.
This allows the valve to operate reliably during normal injection, makes the device relatively compact, and prevents the valve from closing when the spool is lowered.

To this end, in the present invention, a valve chamber has a front part formed in a mold, a rear part formed in a part separated from the mold, and a valve seat formed between the front part and the rear part. A gas vent groove is provided that communicates between the mold cavity and the front of the valve chamber, a gas exhaust port is provided that communicates with the outside of the mold from the rear of the valve chamber, and a gas vent is provided that is separated from the middle of the gas vent groove to connect the valve seat. A bypass is provided that leads to the side of the valve chamber just in front of the valve chamber, and a seat-type valve is placed in the front part of the valve chamber at the valve opening position where the bypass and the rear of the valve chamber communicate, and communication between the bypass and the rear of the valve chamber is blocked. The valve is slidably moved between the valve closed position and the valve closed position, and the valve is closed by the inertia of the molten metal traveling through the gas vent groove before the molten metal traveling through the bypass reaches the valve chamber during injection. A first holding device is provided to hold the valve in the valve open position in such a manner that the valve can be moved from the open position to the valve closed position, and the valve is moved from the valve open position to the valve closed position by the initial inertia of the molten metal. a second holding device that holds the valve in the valve-closed position after the valve has been removed, and a valve-opening device that releases the valve from the valve-closed position when the valve is returned from the valve-closed position to the valve-open position. In the extraction device, a piston cylinder device is provided at the rear of the valve chamber, the rear end of the valve stem of the valve is used as a piston, and the valve is slidably installed in the cylinder, and the valve is opened against the force of the second holding device. A first holding device is provided at the rear of the valve chamber to be releasably installed at a position, a second holding device is provided at the rear of the valve chamber so as to always apply a rearward force to the piston, and the piston cylinder The device is arranged to act as a valve opening device for forcing the piston forwardly against the force of the second retaining device, and the piston-cylinder device is adapted to force the piston rearwardly against the force of the first retaining device. The valve is provided so that it can act as a valve closing device for releasing the valve from the valve open position and moving it to the valve closed position by moving the valve.

In addition, the first holding device is a steel ball type holding device that presses the stepped side of the valve stem, and the second holding device is a holding device using a compression spring or low-pressure fluid pressure that acts on the front surface of the piston. The valve closing device is a valve closing device using high fluid pressure acting on the front surface of the piston, and the valve opening device is a valve opening device using high fluid pressure acting on the rear surface of the piston.

Further, the valve closing device is configured to be actuated by a remote device to forcibly close the valve when the mold is at a low temperature when the molding machine is started, or during low-temperature injection.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

1 and 2 illustrate one embodiment of the present invention, in which the reference numeral 1 indicates a fixed mold, 2 a movable mold, and 1a and 2a a fixed mold and a movable mold. It is a half-shaped seat fitted into each split surface. Here, the seats 1a and 2a are part of a fixed mold 1 and a movable mold 2, respectively. A degassing device 3 is provided at the dividing plane between the fixed mold 1, the movable mold 1, and the movable mold 2, and at an extended position thereof.

On the other hand, the exhaust air reaches the lower part of the gas venting device 3, that is, the front part 11a of the valve chamber 11, which will be described later, from the periphery of the cavity 4 through the gas venting groove 6 from the gas venting path 5 formed on the dividing surface of the mold. A passage has been formed.

As the gas venting device 3, a seat type valve 7 is provided so that the lower surface of the valve head 7a is substantially perpendicular to the gas venting groove 6, and from the middle of the gas venting groove 6 to the lateral direction of the valve head 7a. A gas exhaust passage 8 is provided, which is a bypass that detours to the upper side of the valve head 7a, that is, to the side surface of the valve chamber 11 immediately in front of the valve seat 10, which will be described later. 8a is a hot water pool part.

The valve 7 slides in the axial direction of the spool 9 within the spool 9, which is a valve support member, and when the valve 7 moves upward in FIG. Valve head 7 on seat 10
a contact, and communication between the passage 8 and the rear portion 11b of the valve chamber 11 in the spool 9 is closed. The valve chamber 11 has a front part 11a formed in a mold, a rear part 11b formed in a part separated from the mold, and a valve seat 10 formed between the front part 11a and the rear part 11b. are doing. And the front part 1 of the valve chamber 11
In 1a, the valve head 7a of the seat type valve 7
, the passage 8 which is a bypass is connected to the rear part 11 of the valve chamber 11.
The valve is slidably provided between the open position where the valve b communicates with the valve and the closed position where communication between the passage 8 and the rear part 11b of the valve chamber 11 is cut off. Before reaching the valve chamber 11, the valve 7 can be moved from the valve open position to the valve closed position by the inertial force of the molten metal advancing through the gas vent groove 6.

A rear part 11b of the valve chamber 11 formed around the valve stem 7b is continuous above the valve head 7a, and a discharge port 12 is formed in the rear part 11b of the valve chamber 11.

A spring receiver 13 is fixed to the upper end of the valve stem 7b in the middle of the spool 9.
is slidably fitted in a chamber 14 formed at the upper end of the spool 9, similar to the piston, and includes a spring receiver 13 and a guide member for the valve rod 7b provided on the lower surface of the chamber 14, that is, in the middle of the spool 9. A compression spring 15 is elastically mounted between the valve 9b and the upper surface of the valve 9b, and a force is always applied to the valve 7 in the closing direction. Valve stem 7b
The spring receiver 13 at the rear end is a piston, and the piston and the chamber 14 form a piston cylinder device. The compression spring 15 is connected to the valve 7
This is a type of second holding device that holds the valve 7 in the valve-closed position after it is moved from the valve-open position to the valve-closed position by the initial inertia of the molten metal.

A through hole 9a is formed in the guide member 9b in the middle of the spool 9 in a state perpendicular to the valve stem 7b, and a steel ball 17 is inserted into the through hole 9a while being pressed by a compression spring 16. This steel ball 17 is in contact with a small diameter portion 7c formed in the middle of the valve stem 7b. Further, the pressing force of the compression spring 16 can be adjusted by a push screw 18.

The steel ball 17 is used to stop the valve 7 which is about to be moved upward from the valve open position to the valve closed position by the compression spring 15, which is a second holding device. It is large enough to overcome the force of the attack.

Here, the steel balls 17 and the like provided at the rear of the valve chamber 11 are affected by the inertia of the molten metal traveling through the gas vent groove 6 before the molten metal traveling through the passage 8 reaches the valve chamber 11 during injection. A first holding device is formed to hold the valve 7 in the valve open position in such a manner that the valve 7 can be moved from the valve open position to the valve closed position. Then, the first holding device holds the valve 7.
It is installed in a freely releasable position in the valve opening position against the force of a second holding device consisting of a compression spring 15.

The piston cylinder device is provided so as to act as a valve opening device that moves a spring receiver 13, which is a piston, forward against the force of a second holding device consisting of a compression spring 15, and is also equipped with a steel ball 17, etc. By forcibly moving the piston 13 backwards against the force of the first holding device, it acts as a valve closing device to release the valve 7 from the valve open position and move it to the valve closed position. It is set up like this. The valve opening device is a spring receiver 13
due to high fluid pressure acting on the rear surface of the
The valve closing device was based on high fluid pressure acting on the front surface of the spring receiver 13. Then, when the mold is at a low temperature when the molding machine is started, or during low-speed injection, the electromagnetic switching valves 33, 34, etc., which will be described later, are switched using a remote device, and the valve closing device is activated to forcibly close the valve 7. I made it possible to close it.

Projections 9c, 9c are provided on both sides of the upper end of the spool 9, forming a T-shape.
9a so as to be slidable. This block 19 is connected to a piston rod 21a of a cylinder 21 fixed to a support frame 20 fixed to the fixed mold 1 side.
is fixed at the bottom edge of the

A rotary lever 25 is rotatably supported on the front surface of the block 19 via a thumbscrew 24, and when the rotary lever 25 is in the vertical position, its lower end touches the front surface of the upper end on the spool 9 side. ing. As a result, when the rotating lever 25 is in the vertical position, the spool 9 cannot escape from the T-slot 19a, and when the rotating lever 25 is in the horizontal position,
With the spool 9 and the valve 7 moved above the molds 1 and 2, the spool 9 can be pulled out in the horizontal direction.

Further, the block 19 has a protrusion 1 in a part thereof.
9d, and this protrusion 19d is slidably fitted into a guide rod 28 provided on the side of the support frame 20, and guides the spool 9 when it is raised or lowered, as will be described later.

The block 19 to which the upper end of the spool 9 is connected has a backing plate 2 on the side opposite to the rotating lever 25.
9 is fixed at its upper end with a bolt 30. The lower end of the backing plate 29 extends toward the spool 9 side.

Furthermore, connecting holes 29a and 29b are formed at the lower end and center of the backing plate 29 for connection to an air source, and these connecting holes 29a and 29b are connected to the chamber 14 formed at the upper end of the spool 9. It communicates with through holes 14a and 14b that are continuous at the lower and upper portions. Then, at the edges of the through holes 14a and 14b, the connecting hole 29
O-rings 22 are placed in contact with the edges of a and 29b.
is attached, and the structure is such that the joint between the two can be kept airtight.

The connecting hole 29a has a pipe 31, an electromagnetic switching valve 33,
A compressed air source 35 is connected through the A port of 34, and the B port of the electromagnetic switching valve 33 is connected to the connecting hole 29b through a pipe 32.

A patch plate 29 as described above is provided, and the connection hole 29 is
A, 29b is in contact with the spool 9.
If the structure with the ring 22 is adopted, the spool 9 can be inserted into the T-groove 19a when cleaning the degassing device.
It is possible to easily remove only the spool 9 and valve 7 by pulling it out from the holder. Therefore, the patch plate 29 remains as it is, and the pipes 31 and 32 on the air source 35 side remain as they are on the block 19 side, and there is no need to attach or detach the pipes, making cleaning and maintenance operations extremely easy. Of course, when attaching the spool 9 to the block 19, push the spool 9 into the T-slot 19a,
It can be attached extremely easily by simply pressing it against the backing plate 29 and locking it with the rotating lever 25.

Next, the operation of the embodiment configured as above will be explained.

When starting up the injection molding apparatus, first, the electromagnetic switching valve 34 is turned on for the gas venting device which is raised to a position away from the mold side, and the air source 3 is turned on.
5 to the chamber 14 via the electromagnetic switching valve 33.
Lead it into the lower room. Then, the pressure on the lower side of the spring receiver 13 increases, and the valve 7 is raised against the pressing force of the steel ball 17, and the valve 7 is closed.

Note that the air pressure above the spring receiver 13 is controlled by the solenoid valve 33.
Since the valve 7 escapes to the exhaust port of the valve 7, the upward movement of the valve 7 is performed smoothly.

In this state, the cylinder 21 is operated to lower the entire spool 9. Of course, after the entire spool 9 is lowered, the electromagnetic switching valve 34 can be turned on and the valve 7 can be closed.

When the fixed mold 1 and the movable mold 2 are clamped in this state, low-speed injection can be performed with the valve 7 closed. Although the inertial force of the molten metal is small during low-speed injection, since the valve 7 is closed in advance, the molten metal does not go around to the valve chamber 11 side.

Several shots are performed in this manner until the mold warms up.

On the other hand, after the mold has warmed up, the injection operation is performed by a combination of low-speed injection and high-speed injection, but at this time, the molten metal has a large inertial force, so
There is sufficient force to close the valve 7, and it is necessary to prevent the valve 7 from being closed by the shock when the spool 9 descends.

In this case, both electromagnetic switching valves 33 and 34 are turned on. As a result, air pressure is introduced above the spring receiver 13 having a piston structure, and this air pressure causes the valve 7 to move downward against the force of the compression spring 15, so that the valve 7 remains open. Therefore, even if a shock occurs when the cylinder 21 operates and the spool 9 descends, the valve 7 will not close. At this time,
As the valve 7 descends, the steel ball 17 moves toward the valve stem 7.
The valve 7 is fitted into the small diameter portion 7c formed in the middle of the valve 7, and the valve 7 is held in an open state.

Next, with the mold open, the steel ball 17 is pressed against the lower end step of the small diameter portion 7c of the valve stem 7b, and the spool is pressed with the valve head 7a separated from the valve seat 10, that is, with the valve open. 9 is lowered by operating the cylinder 21. After the spool 9 is lowered, the electromagnetic switching valves 33 and 34 are turned off.

When the fixed mold 1 and the movable mold 2 are clamped in this state, a passage is formed from the cavity 4 to the outside of the spool 9 via the degassing path 5, degassing groove 6, passage 8, and valve chamber 11. .

Then, in this state, an injection plunger (not shown) operates to supply molten metal into the cavity 4. At this time, the molten metal filling the cavity 4 advances through the gas vent passage 5 and the gas vent groove 6, but the gas inside the cavity 4 passes through the passage 8 and the valve chamber 11 and flows toward the discharge port 12. Head over. Note that since the gas has a small mass, the valve 7 will not close due to the action of the gas.

On the other hand, following the gas, the molten metal collides with the lower surface of the valve head 7a. At this time, the impact applied to the valve 7 is much larger than the impact applied to the valve 7 by the gas, as the mass of the molten metal is extremely large compared to the gas, and the inertia is large, causing the valve 7 to be thrown upward. As a result,
The restraining force of the steel ball 17 pressed by the compression spring 16 is released, the valve 7 faces upward, and the upward pulling force of the compression spring 15 is also applied, so that the upper surface of the valve head 7a is seated on the valve seat 10. Aisle 8
and the valve chamber 11 to prevent the outflow of molten metal from the valve 7.
Stop at the position.

At this time, even if the molten metal mixes with the gas in the gas vent path 5 and the gas vent groove 6, becomes a droplet, and hits the valve body discontinuously, the first collision of the molten metal causes the valve body to be blown away. Even if the upward pressure from the molten metal disappears when the gas comes, the valve 7 is given the habit of moving upward by the force of the compression spring 15, so the valve 7 will not block the exhaust passage. It will definitely be done.

Furthermore, as is clear from FIG. 1, since the valve head 7a has an extremely deep recess 7d formed on its lower surface, most of the molten metal and metal powder collide into this recess 7d. The inconvenience that the valve head 7a passes around the valve head 7a and above the valve head 7 is eliminated, and the valve head 7a can be reliably seated on the valve seat 10.

Injection is carried out in this manner, and when the casting operation is completed by pressurized cooling for a predetermined period of time with the valve 7 of the degassing device closed, the mold is opened, the cylinder 21 is operated, and the spool 9 to rise. With this upward movement, the solidified metal filling the cavity 4, gas vent path 5, gas vent groove 6, and passage 8 separates from the valve 7, and the molded product is moved by a product extrusion device (not shown). Remove from mold.

When the cylinder 21 is actuated and the entire spool 9 is pulled up, air pressure is applied to the spring receiver 13 as described above, and the spring receiver 13 is pulled up from the compression spring 1.
5, push downward to open the valve 7, and clean the valve head 7a, valve seat 10, etc. with compressed air.

In addition, if you wish to clean or maintain the entire degassing device 3, loosen the bell screw 24, rotate the rotating lever 25 approximately 90 degrees, and move it from the vertical position to the horizontal position. The protruding portion 9c formed in the portion can be easily removed from the T-slot 19a, and the entire spool 9 can be removed extremely easily.

Since this embodiment is configured as described above,
It is possible to remotely open and close the valve using air pressure without using a conventional mechanical stopper mechanism, which not only makes the device more compact, but also eliminates cumbersome and dangerous operations such as adjusting the valve by the operator. The valve can be opened and closed without any movement.

Of course, this device can perform injection only at low speed even when the mold is at a low temperature when the molding machine is started, and the inertial force of the molten metal is small, as well as when the mold temperature has reached the desired temperature. Since the inertial force of the molten metal may be small when injection is performed, the valve 7 can be closed in advance before injection.

FIG. 3 explains another embodiment of the present invention, and is shown in a simplified manner except for parts necessary for explanation.

In this embodiment, a spring 15 that constantly presses upward the spring receiver 13 having a piston structure is used.
The pipes 31 and 32 are inserted into the through holes 29a and 29b.
Connect the electromagnetic switching valve 33 via the electromagnetic switching valve 3
An electromagnetic switching valve 36 and a pressure reducing valve 37 are provided between the electromagnetic switching valve 33 and the air source 35 in this order from the electromagnetic switching valve 33 side.

Since this embodiment employs the above-described structure, if the electromagnetic switching valves 33 and 36 are turned off during low-speed injection at the initial stage of operation of the injection molding apparatus, the pressure reducing valve 37 can maintain the predetermined pressure. The reduced air pressure is supplied to the lower side of the piston corresponding to the spring receiver 13 of the chamber 14. In this case, the low-pressure fluid pressure retaining device acting on the front side of the piston forms a second retaining device.

If the pressure at this time is set to a value slightly smaller than the pressing force by the steel ball 17, which is the first holding device, the valve 7 can be kept open. An upward force is applied to the valve 7, and the valve 7 is prevented from opening after the valve 7 is closed. That is, the air pressure introduced through the pressure reducing valve 37 plays the role of the spring 15 in the embodiment shown in FIGS. 1 and 2.
In this case, if the inertial force of the molten metal acts on the valve 7 during injection, the valve closes.

Note that when the electromagnetic switching valve 36 is turned on, the spring receiver 13 is forcibly pushed up by the high pressure of the compressed air source 35, and the valve 7 is closed. in this way,
If the valve 7 is set on the mold side with the valve 7 closed by air pressure and the test shot is performed at the beginning of operation by low-speed injection, even if the inertia of the molten metal is small and there is not enough force to close the valve 7, Molten metal does not go around to the valve chamber side.

On the other hand, when the mold warms up and normal injection molding is performed by a combination of low-speed injection and high-speed injection, the spool 9 is in the raised position by the cylinder 21, and the electromagnetic switching is performed with the mold open. valve 33,
36 is turned on, the pressure of the air source 35 reaches the upper side of the spring receiver 13 of the piston structure. As a result,
Valve 7 is forced open. Therefore, the valve 7 will not be closed by the shock when the spool 9 is lowered by the cylinder 21.

Since this embodiment is configured as described above,
The same effects as the above-mentioned embodiment can be obtained, and
It is not necessary to provide the compression spring 15, the number of parts is reduced, and assembly is facilitated.

As is clear from the above description, according to the present invention, the gas venting valve can be closed by the action of inertia of the molten metal during injection, thereby ensuring that the gas is not discharged from the mold cavity during injection. easy to do,
You can always easily obtain a mold-free injection product. Furthermore, by using the second holding device, the once-closed valve can be prevented from opening during injection, and the present device can be used semi-permanently.

In addition, because the valve can be forcibly opened and closed using fluid pressure and can be remotely controlled, there is no need for a mechanical stopper mechanism to open the valve as in the past. is simplified.

Furthermore, since the operator does not have to manually open and close the valve, it is possible to operate the valve reliably without any trouble or danger.

Furthermore, since there is no need to attach a lever for a stopper mechanism to the valve, the mass of the valve can be reduced and the inertia of the valve can be reduced, so the responsiveness of the valve's opening and closing operations can be significantly improved. .

Of course, since the upper end of the valve stem has a piston structure and a configuration is adopted in which fluid pressure is applied to the front chamber, the valve can be closed by remote control when testing at the start of operation. When the mold temperature is low or during low-speed injection, the valve does not close and molten metal enters the valve chamber, which prevents inconvenient accidents and prevents molten metal from entering the valve chamber by manually blocking the passage. There's no need to. Also,
Since it uses a structure that applies fluid pressure to the rear chamber of the piston structure, the valve does not close even if there is a shock when the spool is lowered, and the spool is lowered with the valve open, maintaining normal gas venting function. can be done. and a first holding device that holds the valve in the valve open position and a second holding device that holds the valve in the valve closed position.
The use of the holding device makes the operation of the device more reliable.

[Brief explanation of the drawing]

1 and 2 are a vertical side view and a partially sectional front view showing one embodiment of the present invention, and FIG. 3 is an air circuit diagram showing another embodiment of the present invention. 1... Fixed mold, 2... Movable mold, 3... Gas venting device, 4... Cavity, 7... Valve, 9...
Spool, 10... Valve seat, 11... Valve chamber, 13...
...Spring receiver, 15, 16... Compression spring, 17...
Steel ball, 19...Block, 19a...
T groove, 21... cylinder, 25... rotating lever,
33, 34, 36... Solenoid switching valve, 35... Compressed air source, 37... Pressure reducing valve.

Claims (1)

[Claims] 1. A valve chamber having a front part formed in a mold, a rear part formed in a part separated from the mold, and a valve seat formed between the front part and the rear part. A gas vent groove is provided that communicates the mold cavity with the front part of the valve chamber, and a gas exhaust port is provided that communicates with the outside of the mold from the rear of the valve chamber. A bypass communicating with the side of the valve chamber immediately before the valve chamber is provided, and a seat-type valve is placed in the front part of the valve chamber at the valve opening position where the bypass and the rear part of the valve chamber communicate, and when the communication between the bypass and the rear part of the valve chamber is cut off. During injection, the valve is opened by the inertia of the molten metal traveling through the gas vent groove before the molten metal traveling through the bypass reaches the valve chamber. A first holding device is provided for holding the valve in an open position such that the valve can be moved from the open position to the closed position by the initial inertia of the molten metal. A second holding device is provided to hold the valve in the valve-closed position after the valve has been removed, and a valve-opening device is provided to release the valve from the valve-closed position when the valve is returned from the valve-closed position to the valve-open position. In the device, a piston cylinder device is provided at the rear of the valve chamber, the rear end of the valve stem of the valve is used as a piston and is slidably provided in the cylinder, and the valve is moved to the valve open position against the force of the second holding device. A first holding device is installed at the rear of the valve chamber, and the second time keeping device is installed at the rear of the valve chamber so as to keep a rearward force acting on the piston at all times. The device is arranged to act as a valve opening device for forcing the piston forwardly against the force of the second retaining device, and the piston-cylinder device is adapted to force the piston rearwardly against the force of the first retaining device. 1. A degassing device for a mold, characterized in that it is provided so as to be able to function as a valve closing device that releases a valve from a valve open position and moves it to a valve closed position by moving the valve. 2. The first holding device is a steel ball type holding device that presses the stepped side surface of the valve stem, and the second holding device is a holding device using a compression spring or low-pressure fluid pressure acting on the front surface of the piston. Claim 1, wherein the valve closing device is a valve closing device using high fluid pressure acting on the front surface of the piston, and the valve opening device is a valve opening device using high pressure fluid pressure acting on the rear surface of the piston. Gas venting device for molds. 3. Claim 1, wherein the valve closing device is configured to be operated by a remote device to forcibly close the valve when the mold is at a low temperature when the molding machine is started, or during low-temperature injection. Degassing device for the mold described.