JP2790470B2 - Degassing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas discharge device for casting, and more particularly to a gas release device that can be suitably used in, for example, an injection molding operation.

BACKGROUND OF THE INVENTION In an injection molding process, molten metal is injected into a cavity having a mold corresponding to the shape of a cast product to be a finished product. To avoid substantially wasteful injection molding, the cavities are placed under suction to remove as much gaseous material from the cavities through the process of injecting the molten metal.

One type of commonly used gas exhaust mechanism employs a shut-off valve to control the extraction of gas from the cavity through a gas exhaust passage. The valve is kept open during the injection process, and when the cavity is filled with the molten metal, the valve is closed so that the suction source does not suck the excess molten metal. This is because this kind of excess molten metal may flow out of the cavity through the degassing passage.

A conventional degassing device using a valve according to the prior art
There are two types. These typically include a reciprocally movable valve body that cooperates with an annular seating site. In one type, the operation of the valve body with respect to the closed position is achieved by a positive driving mechanism synchronized with the injection operation of the molten metal, and the valve element is closed when the cavity is filled with the molten metal. U.S. Pat. No. 3,121,926 discloses a mechanism of this type as one embodiment.
That is, US Pat. No. 3,121,926 discloses a configuration in which a trigger switch driven by an injection ram starts a closing operation of a valve. US Patent 4,46
No. 3,793 discloses another embodiment of such a device.

Another type of valve mechanism used in the prior art includes a valve element driven by molten metal.
In this mechanism, the operation of the valve body directed to the closed position is performed by the pressure obtained by the molten metal itself directly in contact with the valve body,
That is, achieved by dynamic forces.

As disclosed in U.S. Pat. No. 4,431,047, in various prior art embodiments, the valve element is opened under the resilience of a spring, wherein the dynamic force of the molten metal is increased by the resilience of the spring. Overcoming the force displaces the valve body to the closed position. However, as recognized by the same inventor, U.S. Pat. No. 4,489,771 following U.S. Pat. No. 4,431,047, such structures are not necessarily complete. That is, the intermittent collision of the molten metal causes the valve body to oscillate, and as a result, the pressure on the valve body recovers from time to time, thereby allowing the valve body to be opened again.

If the valve body is occasionally opened in the presence of the melt, it will cause a clogging of the sealing surface and allow the melt to enter the degassing chamber. Accordingly, U.S. Pat.
No. 489,771 provides a mechanism for applying a complicated bias and triggering in order to reverse the biasing force on the valve element when the molten metal initially collides with the valve element, that is, to direct the valve element to a closed state. ing.

However, this structure may be able to eliminate the oscillating action of the valve body, but when the molten metal reaches the seating portion of the valve body and hinders the valve body from being closed, the valve body is removed. It is not clear as to whether the resilience to close the valve element is sufficient in all cases of closing the seating portion.

U.S. Pat. No. 3,885,618 discloses a valve body structure driven by molten metal that floats freely in a valve chamber when the mold is in a closed state. U.S. Pat. No. 3,885,618 relies on a structure in which the valve element achieves a sufficient sealing effect when retracting into the seat.

However, there is no guarantee that the melt pressure that actually acts on the valve body will be able to overcome obstacles that may exist between the sealing surfaces. This type of obstacle is caused by solidified molten metal that has scattered through the valve body and reached the seating position.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to overcome the above-mentioned drawbacks and disadvantages of the prior art, and has been described in view of the fact that when a cavity is filled with a molten metal, a degassing system precedes valve closing. It is an object of the present invention to provide a degassing device in a casting process in which a molten metal can be substantially prevented from entering the inside of a casting, and a suction system can be substantially shut off from the cavity.

Another object of the present invention is to provide a gas venting device having a mechanism for overcoming an obstacle existing between a valve body and a seating portion and positively closing the valve body.

Another object of the present invention is to provide a degassing device which can divert a molten metal which travels through a degassing passage to a detour passage having a flow resistance so as to prevent the molten metal from entering the inside of a degassing system. The purpose is to provide.

Still another object of the present invention is that even when the molten metal that proceeds through the gas vent passage captures a driven valve element, the valve element is more quickly directed to a closed state than by the molten metal itself. The present invention provides a degassing device that can move forward in the forward direction, thereby substantially preventing the molten metal from entering the inside of the degassing system even in all situations.

These and other objects of the present invention are directed to a mold having a cavity for filling the melt, a means for injecting the melt into the cavity of the mold, and the cavity being filled before the melt progresses as the melt fills the cavity. This is achieved by a degassing device used in a mold apparatus that includes a cavity for discharging gas from the tubing and a gas discharge passage communicating with the cavity. The degassing device comprises a housing having a valve chamber including an inlet disposed in fluid communication with the gas discharge passage and a discharge port for discharging gas from the valve chamber. An annular seating portion for the valve body adjacent the inlet cooperates with the valve chamber and a valve body coaxial with the valve seating portion, the valve body extending rearward through the valve chamber away from the mold. The valve stem. The valve body may be axially movable toward the mold to open the inlet, and may move rearward away from the mold to close the inlet in cooperation with the seat. It is possible.

A set of detection means is provided, one of which detects that the injection ram has reached a preset position within the stroke of the ram in its operating state, and Generates a signal in response. The valve driving means is disposed in association with the housing, and positively activates the inlet before the molten metal which advances to the valve body in response to the signal from the signal generating means reaches and before contacting the bottom surface of the valve body. The valve body is connected to a valve stem for driving the valve body backward to close the valve body. The valve driving means is preferably driven to advance the valve body so as to forcibly open the inlet before the molten metal is injected into the cavity of the mold. This can include a reversible fluid cylinder as well as a piston that operates on a reciprocable drive member connected to the valve stem.

The joint member allows the valve body to freely move between the open position and the closed position when the fluid cylinder is not pressurized. This is to allow the operator to check for any obstacles such as inside the cavity when the mold is in the open state.

Means for Achieving the Object In order to achieve the above object, the present invention provides a mold having a cavity filled with a molten metal under a driving action of an injection ram, and injects the molten metal into the cavity of the mold. Means having a means and a gas discharge passage communicating with said cavity to discharge gas from said cavity prior to said advancing molten metal as said molten metal is filled into said mold cavity, said device comprising: A housing having a valve chamber defined with an inlet disposed in fluid communication with the gas discharge passage and a discharge port for discharging gas from the valve chamber; and a housing provided proximate to the inlet. An annular valve seat, the valve seat being coaxial with the valve seat and the valve chamber and spaced from the mold. A valve body having a valve stem extending rearward through a valve chamber, and detecting that the injection ram has reached a predetermined position on a stroke in a step of injecting the molten metal into the cavity and performing the detection. Means for generating a signal in response to operation, and for a reversible fluid provided in a bore in a housing having a drive rod coaxial with the valve stem and extending forwardly toward the valve stem. A cylinder / piston assembly, located in the housing, at an intermediate portion between the valve chamber and the return-type fluid cylinder / piston assembly, before the advancing molten metal arrives, and in contact with the bottom surface of the valve body Prior to the operation, the rearward movement of the drive rod is transmitted to the valve stem in response to a signal from the signal generating means to close the inlet and A connection between the drive rod and the valve stem for transmitting forward movement of the drive rod to the valve stem to forcibly open the inlet before the molten metal is injected into the cavity; The valve body is operable to move forward to open the inlet toward the mold, and further to retract the inside of the valve seat to close the inlet. The coupling means includes a first front shoulder provided at an end of the valve stem, a first rear shoulder provided at an end of the drive rod, and the valve. A second rear surface that deflects the ends of the stem and the drive rod and cooperates with the first front shoulder and the first rear shoulder provided on the valve stem and the drive rod, respectively. A slidable joint member having a shoulder and a second front shoulder, wherein the gap defined between the second front shoulder and the second rear shoulder of the slidable joint member is the valve. The space is selected to be larger than the minimum space at the first front shoulder and the first rear shoulder provided at the end of the stem and the drive rod, and the gas discharge passage is provided when the valve body moves forward. And a detour passage for diverting gas entering through the gas discharge passage and leading it to a passage surrounding the valve stem. And the bypass path is a flat space defined on a side of a cylindrical chamber.

Embodiments Other objects and advantages of the present invention will be readily understood from preferred embodiments of the present invention described in detail below with reference to the accompanying drawings.

1 to 4, the die casting apparatus is schematically shown as a sectional view. The die casting apparatus comprises a die having a fixed mold 2 and a movable mold 3, that is, a mold 1, and a mold cavity 4 is defined between the two fixed molds 2 and the movable mold 3. The injection chamber 5 is in communication with the mold cavity 4 via a passage 6. The injection chamber 5 is supplied with molten metal 7 from a crucible 8 or another molten metal supply source via a funnel 9. The injection ram 10 drives the injection piston 11 through the injection chamber 5 to force the molten metal 7 into the cavity 4.

The degassing device 100 according to the present invention is provided in association with a gas discharge mechanism, and functions to remove gas from the cavity 4 through the gas discharge passage 12 while the injection process is performed. As shown more clearly in FIGS. 5 to 7, the gas discharge passage 12 is in communication with the chamber 13, and a valve 106 to be described later can enter the interior of the chamber 13.

Actually, narrow bypass passages 14 and 14 are defined on both sides of the chamber 13, and the passages 14 and 14 communicate with a space around a valve stem 126, which will be described later, formed integrally with the valve body 106. In state.

The valve chamber 102 accommodates a valve seat 104, and the valve seat 104 cooperates with a reciprocally movable valve body 106 at a lower end thereof. As is easily understood from the figure,
The lower end surface 106a of the valve body 106 is formed to be inclined.

A flange-shaped stopper 127 is formed on the upper part. The outer shape of this stopper 127 is valve seat 1
The stopper has substantially the same diameter as the interior wall defined in FIG. 04 and serves to prevent fine powder of molten metal, dust and the like from entering the coupling chamber 122 side.
When 127 abuts on the inner wall surface at the top of the valve seat, it acts to reduce the impact per unit area in its wide area. The valve 106 functions to open and close a gas inlet, that is, an inlet 108 at the lower end of the valve chamber 102. The gas inlet 108 is formed so as to be inclined corresponding to the lower end inclined surface 106a of the valve body 106. The gas discharge port 110 is connected to a vacuum suction source or a negative pressure device (not shown), and is connected to the gas discharge passage 12, the chamber 13, and the inlet.
When the valve body 106 is at the lower end portion, i.e., in the open position, via 108, it sucks in through the gas discharge passage 12 and the chamber 13, while
When the valve body 106 is located at the uppermost end of the bypass gas vent passages 14, 14, it functions to sit on the valve seat 104 and shut off gas.

The valve body 106 is connected to a pneumatic cylinder / piston assembly 112, as will be described later, and the cylinder / piston assembly 112 is used to open and close the inlet 108.
The 106 is moved forward, ie, displaced toward the mold, and retracted, ie, displaced in a direction away from the mold.

As will be appreciated with reference to FIGS. 1 to 4, the pneumatic cylinder and piston assembly 112 is controlled via a solenoid valve 15 which is connected to a compressed air supply indicated by reference numeral 16. The position of the solenoid valve 15 is determined by a control circuit incorporating a set of limit switches 17,18. The limit switches 17 and 18 detect a predetermined position of the injection piston 11 in cooperation with a cam 19 arranged on the drive shaft of the injection ram 10.

The molding, that is, the die casting process will be schematically described with reference to FIGS.

FIG. 1 shows a state of the system before the molten metal is injected into the cavity 4. That is, first, the solenoid valve 15 is switched as shown in FIG. 1, and the valve body 106 is moved to the uppermost position, in other words, through the compressed air supplied from the compressed air supply source 16 to the pneumatic cylinder / piston assembly 112. If so, it will be held in the closed position.

Next, the injection process is started by a manual operation or the like. The injection ram 10 moves to the left in FIG. 1 through the injection chamber, and the piston 11
Is supplied from the crucible 8 and feeds the molten metal 7 in the injection chamber 5 into the cavity 4. By moving the ram 10 further leftward, the cam 19 is moved to one of the limit switches 17.
Engage with. The output signal of the limit switch 17 is used for urging a vacuum suction source (not shown) and for switching the solenoid valve 15. That is, the solenoid valve 15 is
As shown in the figure, the switching operation is performed, and the compressed air from the compressed air supply source 16 causes the piston 18 of the pneumatic cylinder / piston assembly 112 to descend, whereby the valve body 106 performs the forward operation. As a result, the cavity 4, gas exhaust passage 12, chamber
The air, gas and the like in the passage 13 and the passages 14 and 14 are sucked through the vacuum suction source (not shown).

When the piston of the pneumatic cylinder / piston assembly 112 reaches the most advanced position, the proximity switch 152 described later detects this, and a timer (not shown) starts counting.
During this time, the pneumatic cylinder / piston assembly 112 presses the valve body 106 to keep the gas discharge passage 12 closed.

When the timer counts up a predetermined time, the count-up signal deactivates the solenoid valve 15, and the solenoid valve 15 maintains the neutral position and opens the valve body 106 as shown in FIG. Maintained condition. By maintaining the valve body 106 in the open state in this way, when the molten metal attempts to enter through the bypass passages 14, a closed state can be obtained between the valve body and the valve seat in a prompt response. At this time, it will be easily understood from the figure that the cam 19 is located between the limit switches 17 and 18.

The piston 11 further moves forward and continues to engage the cam 19 with the limit switch 18. As a result, the output signal from the limit switch 18 is sent to the solenoid valve 15, and the solenoid valve 15 is switched to the position shown in FIG. For this reason, the piston 118 of the pneumatic cylinder / piston assembly 112 performs a retreat operation, and finally the valve body
106 is seated on the valve seat 104, and the gas exhaust port 110
And the passage 12 is disconnected. That is, the stopper
127 When it comes into contact with the uppermost end of the inner wall of the valve seat 104,
6 cuts off the communication between the gas discharge port 110 and the passage 12. When the pair of adjustment bolts 130, 130 are screwed, the seat blocks 128, 128 screwed thereto are displaced on an inclined surface formed on the top of the valve seat 104, and the position of the valve seat 104 can be adjusted. It is.

As described above, the upward movement of the valve element 106 is caused by the molten metal entering through the gas exhaust passage 12
Prior to entering the interior of 102, inlet 108 is sufficiently closed. In this way, once the molding process is completed, the movable mold 3 is opened, the molded product is removed from the mold, and the excess molten metal is removed from the gas discharge passage 12 and the lower surface of the valve body 106. The solenoid valve 15 in the position shown in FIG. 1 forcibly lowers the valve body 106 again through the compressed air supply source indicated by the reference numeral 16 and shifts the valve body 106 to the open state. Facilitates cleaning. When the cleaning is completed and the mold returns to its original position again, the casting process can be restarted.

The degassing device according to the present invention will be described in more detail with reference to FIGS. 5, 6, 7 and 9.

The valve chamber 102 is contained inside a housing 114,
The pneumatic cylinder / piston assembly 112 is located at the top, or tail end. The assembly 112 includes the piston 1
A driving member extending into the interior of the coupling chamber 122;
That is, it is connected to the drive rod 120. The valve element 106 is inserted into the end of the valve stem 126, and the valve stem 1
26 passes through valve chamber 102 and couples into coupling chamber 1
It extends to the rear of 22. The position of the valve seat 104 is adjustable by seat blocks 128 having tapered surfaces. The seat blocks 128, 128 are adjustment bolts
By means of 130, 130, it is possible to adjust manually from the outside.

The drive rod 120 and the valve stem 126 are coaxial and their ends are indirectly connected by a slidable joint member 132 located inside the coupling chamber 122. Valve stem nut 134 has a shoulder 136 threaded to the end of valve stem 126 and facing forward thereof. This shoulder 136 cooperates with a rearward facing shoulder 138 at the distal end of the sliding joint member 132. Similarly, the drive rod nut 1 screwed into the end of the drive rod 120
40 has a rearwardly facing shoulder 142 which is configured to cooperate with a forwardly facing shoulder 144 at the rear end of the joint member 132. Coupling chamber 12
Inside 2, a coupling coil spring 146 imparts a forward resilient force to a front end 148 of the coupling chamber 122 to a joint member 132 that slides toward a foremost portion. The forward spring force of the coil spring 146 is selected to be greater than the backward spring force of the spring 124. Accordingly, when the valve body 106 is at its forward end, that is, in the open state and the cylinder 116 is in the non-pressurized state, the movable part is in the state shown in FIG. That is, the separation distance S1 is set between the valve stem nut 134 and the driving rod nut 140.

In this so-called check position, the valve body 106 and the valve stem 126 can be freely displaced, which means that the operator has to move the valve body 106 before the mold is closed again to carry out the further casting process. Allows manual checking of freedom of movement.

The sizes and spaces of the various components of the degassing device are as follows.

The valve body 106 and the valve stem 126 secure a stroke S defined between the open position shown in FIGS. 5 and 7 and the closed position shown in FIG. That is, in the fully opened position shown in FIGS. 5 and 7, the valve element 106 closes the gas vent passages 14 and 14, while in the fully closed position shown in FIG. Retreats inside 104.

The shoulder 150 of the valve stem 126 is located at a space S5 away from the rear end of the valve seat 104 in the open position. In this case, the space S5 is equal to or larger than the stroke S. This space S5 is a valve
When the valve 106 is about to close, the valve body 106 is allowed to move the entire stroke. Similarly, when the sliding joint member 132 is in its leading end position, the space S4 must be equal to or greater than the stroke S between its rear end and the rear end of the coupling chamber 122 ( (See FIG. 5). This also ensures a space S6 between the rear end of the piston 118 and the rear end of the cylinder 116. That is, the rearward displacement of the piston 118 causes the driving rod nut 140 to act to raise the joint member 132, and then acts to raise the valve stem nut 134 together with the valve stem 126 and the valve body 106.

The gap G between the front shoulder 138 and the rear shoulder 144 of the sliding joint member 132 is greater than the minimum space S3 between the shoulder 142 of the driving rod nut 140 and the shoulder 136 of the valve stem nut 134. S2 must be taken larger. This distance S2 is at least equal to the stroke S. Of course, space S1 must be equal to space S2 (see FIG. 5).

It is also possible to use auxiliary control means in order to obtain data on the position of certain actuating members constituting the degassing device. In this case, it can be used for an automatic control system if desired.

Thus, magnetic or optical sensor 152 detects the position of valve stem nut 134, while magnetic limit switches 154, 156 detect the position of piston 118 within cylinder 116. If necessary, further position sensors and a controller can be provided, by means of which the status of the various operating elements of the degassing device can be indicated.

8a to 8c are sectional views taken along lines AA, BB and CC of FIG. As indicated by the dashed line, the housing
114, the valve seat 104, the joint member 132, the valve stem 126, and the like are closed by a flat plate.
However, if the plate is removed, the valve seat 104, the joint member 132, and the valve stem 126 can be easily removed. This is to simplify the manual check.

The operation of the degassing device according to the present invention will be described below in detail with reference to FIGS.

FIG. 5 shows the structure of the apparatus when the cylinder 116 is pressurized and the driving valve stem 126 advances, whereby the valve body 106 is forcibly moved to the open position. This is typically performed after opening the mold to return the valve 106 to indicate its open position for cleaning and sensors. The pressure on the rear side of the cylinder 116 is reduced before the mold is reclosed. As a result, the operating portion becomes the seventh
As shown in the figure, it is possible to confirm that the valve stem 126 is in the lowered state. As already described above, the joint member 132 in which the driving rod nut 140 can slide due to the relative elasticity of the springs 124 and 146.
While close to the rear shoulder 144, the joint member 1
32 secures its tip position. This leaves the valve body 106 movably, so that the operator can check for the presence of an obstacle in or around the inlet 108 and confirm that the valve body 106 moves freely. I can do it.

FIG. 5 shows the state of the apparatus while the molten metal is in the injection stage. At this time, the gas is supplied to the gas discharge passage 12, the chamber 13, the bypass passages 14, 14, the inlet 108, and the gas discharge port 110.
Is derived from That is, the gas that precedes the molten metal passes through the passage 12 and the chamber 13 and then is directed to the bypass passages 14 and 14 so as to bypass the valve body 106. Then, inlet 10
As a result, the gas is discharged to the outside from the gas discharge port 110.

In this case, even if the molten metal reaches the gas discharge passage 12 and the chamber 13, the molten metal is effectively prevented from reaching the inlet 108. That is, the detour passages 14 and 14
As can be readily appreciated from Figures a and b, it is formed from a set of substantially flat spaces. Therefore, even when the molten metal enters the bypass passage 14, the flow resistance is extremely large and does not easily reach the inlet 108. Therefore, in this state, the pneumatic cylinder
The piston assembly 112 maintains the valve stem 126 and the valve body 106 in a balanced state so that the valve stem 126 and the valve body 106 can be driven backward while the valve body 106 is maintained in the open state. That is, the compressed air
When introduced into the lower port of 6, the valve stem 126 and valve body
106 moves backward and reaches the closed position.

As shown in FIG. 6, when this state is reached, the valve stem 126 and the valve body 106 are driven rearward at an extremely high speed. As shown in FIG. 5, FIG. 6 and FIG.
The front surface of the valve seat 106 and the front end of the valve seat 104 are secured so as to be inclined at a predetermined angle with respect to a plane perpendicular to the axis of the valve element and the valve stem. This facilitates removal of the molten metal adhering to the surfaces of the valve body 106 and the valve seat 104. Furthermore, it is possible to carry out the cleaning operation by removing the bolted degassing device from a predetermined position on the mold.

Next, FIGS. 10a and 10b show another embodiment of the present invention.
In this embodiment, the same components as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, in particular, a flow resistor having a triangular cross section or serration is disposed at a portion defining the detour passages 14, 14 so as to be uneven, preferably perpendicular to the gas discharge direction. Therefore, the molten metal is provisional
Even if an attempt is made to enter the inlet 108 via 14, the step structure increases the flow resistance and does not hinder the displacement operation of the valve body 106.

As will be easily understood from the above, the object can be effectively achieved by the degassing device according to the present invention. The pneumatic cylinder and piston assembly 112 provides a sufficient closing force to the valve body, thereby
Help them overcome obstacles.

Although the invention is said to be usable in connection with the die casting process, this degassing device according to the invention is likewise applicable to other types with gas discharge, such as injection molding devices using thermoplastics or other substances. It is also possible to use it for a casting device.

Variations of the preferred embodiment disclosed will be apparent to those skilled in the art. For example, cylinder / piston assembly 112
Is applicable to being driven by hydraulic pressure rather than by air pressure. Other coupling means than those disclosed in coupling chamber 122 can be employed as long as they achieve substantially the same function.

As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. Of course.

[Brief description of the drawings]

1, 2, 3 and 4 are schematic illustrations of a die casting apparatus cooperating with the degassing apparatus according to the present invention, showing an extension stage of the die and degassing operation, and FIG. Figure,
6 and 7 are longitudinal sectional views of the gas venting apparatus of the present invention showing different stages of the die casting and gas discharging operations, and FIGS. 8a to 8c are lines AA and BB of FIG. 7, respectively. And C-
9A is an enlarged longitudinal sectional view of the gas venting device according to the present invention, FIG. 9B is a cross sectional explanatory view of the gas venting portion of FIG. 9A, and FIG. FIG. 10b is a longitudinal sectional view of another embodiment of the degassing device, and FIG. 10b is a longitudinal sectional view of the degassing portion of FIG. 10a. DESCRIPTION OF SYMBOLS 1 ... Mold, 2 ... Fixed mold 3 ... Movable mold, 4 ... Cavity 5 ... Injection chamber, 12 ... Gas discharge passage 13 ... Chamber, 14, 14 ... Detour passage 100 ... Gas release Apparatus 102 Valve chamber 104 Valve seat 106 Valve 108 Inlet 110 Gas exhaust port 112 Pneumatic cylinder / piston assembly 118 Piston 122 Coupling chamber 126 Valve stem, 127 Stopper 128, 128 Seat block 130, 130 Adjustment bolt 132 Joint member 140 Drive rod nut

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-180354 (JP, A) JP-A-1-40159 (JP, A) JP-A-6-122051 (JP, U) JP-A-62-1 109849 (JP, U) Shokai Sho 61-17267 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 17/14, 17/22

Claims (1)

(57) [Claims] 1. A mold having a cavity filled with a molten metal under the driving action of an injection ram, means for injecting the molten metal into the cavity of the mold, and A gas discharge passage communicating with said cavity for discharging gas from said cavity prior to said device, said device comprising an inlet arranged to be in fluid communication with said gas discharge passage. A housing having a formed valve chamber and a discharge port for discharging gas from the valve chamber, an annular valve seat provided in close proximity to the inlet, and coaxial with the valve seat and the valve chamber. A valve body having a valve stem extending away from the mold and rearwardly through the valve chamber Means for detecting that the injection ram has reached a predetermined position on a stroke in a step of injecting the molten metal into the cavity and generating a signal in response to the detection operation; and A reversible fluid cylinder / piston assembly provided in a bore of a housing having a drive rod that is coaxial and extends forwardly toward the valve stem; In response to a signal from the signal generating means, the driving mechanism is disposed at an intermediate portion of the return-type fluid cylinder / piston assembly and before the traveling molten metal arrives and before contacting the bottom surface of the valve body. The rearward movement of the rod is transmitted to the valve stem to close the inlet, and the inlet is closed before the molten metal is injected into the cavity. Braking manner consists of a coupling means connected between the drive rod and the valve stem for transmitting the operation to the front of the drive rod relative to the valve stem so as to open,
The valve body is operable to move forward to open the inlet toward a mold, and is further operable to move backward within the valve seat to move away from the mold to close the inlet to close the inlet, The coupling means surrounds a first front shoulder provided at an end of the valve stem, a first rear shoulder provided at an end of the drive rod, and an end of the valve stem and the drive rod. And a slidable joint member having a second rear shoulder and a second front shoulder cooperating with the first front shoulder and the first rear shoulder provided on the valve stem and the drive rod, respectively. And a gap defined between a second front shoulder and a second rear shoulder of the slidable joint member includes a first front shoulder provided at an end of the valve stem and the drive rod; First It is selected to be larger than the minimum space at the rear shoulder, and the gas discharge passage communicates with a substantially cylindrical chamber that enters when the valve body moves forward, and the chamber further comprises The gas entering through the gas discharge passage is branched and communicated with a bypass passage for leading the valve stem toward the passage surrounding the valve stem, and the bypass passage is defined on a side portion of the cylindrical chamber. A degassing device characterized by being a flat space.