Method for acknowledging operation phase of gas venting device in injection molding apparatus and acknowledging means therefor

Abstract

 In an injection molding apparatus, provided are a main die-casting section, a gas venting arrangement for discharging gas from a mold cavity, and means for acknowledging operation mode of the gas venting arrangement. The gas venting arrangement has a gas vent control valve for opening and closing a gas vent passage in communication with the mold cavity. The acknowledging means checks actual period starting from a molten metal detection at the gas vent passage and ending at a timing of complete closure of the gas vent control valve. A comparator is provided for comparing the actual period with a normal set period. If the actual period is outside the normal period, alarm signal is generated for notifying an operator of any abnormality in the gas venting arrangement.

Description

[0001] The present invention relates to a method for acknowledging an operation phase of a gas venting device for use in an injection molding apparatus, and an acknowledging means for acknowledging the operation phase of the gas venting device.

[0002] In a conventional molding apparatus such as a die casting machine, a gas vent control valve is provided at an exit end of a gas venting passage formed in a metal mold and in fluid communication with a mold cavity in order to produce a molded product free from voids. More specifically, a molten metal is filled in the mold cavity while opening the gas vent control valve so as to discharge gas in the mold cavity toward outside of the metal mold through the gas vent passage and through the valve. Further, a molten metal detection means is provided which generates a signal indicative of the molten metal detection at a predetermined position. In response to the detection signal, the gas vent control valve is forcibly closed so as to avoid overflow of the molten metal through the valve. Such conventional structure is disclosed in Japanese Patent Application Kokai Nos.59-130670 and 62-34657 and Japanese Utility Model Publication No. 59-19554.

[0003] In the conventional gas venting arrangement described above, several checkings are required prior to actual injection molding. For example, a position of the gas vent control valve must be checked. Further, the valve closing operation must be provisionally checked prior to the molten metal injection in order to investigate malfunction of the valve. In other words, due to the inherent constructions of the conventional arrangement, operational acknowledgements can only be made with respect to the complete immobility of the valve and the continuous valve stop at its close position.

[0004] However, there are other important checking items. For example, if degraded is the performance of a valve driving mechanism which moves the gas vent control valve to its close position upon detection of the molten metal, the molten metal may overflow through the gas vent control valve. Further, a pneumatic source is applied to the valve driving mechanism as a power source for operating the latter. In this case, if the pressure reduction occurs in the pneumatic source, the valve driving mechanism cannot be sufficiently operated, to thereby lower a moving speed of the gas vent control valve, to thus retard a closing timing thereof. As a result, molten metal overflow may occur. In this connection, it is also necessary to check the degradation of the performance of the valve driving mechanism and pressure reduction in the pneumatic source. However, such type of checkings are not achievable in the conventional arrangement.

[0005] It is therefore, an object of the present invention to provide a method and means for acknowledging an operation mode of a gas venting arrangement in an injection molding apparatus.

[0006] Another object of the invention is to provide such method and means capable of acknowledging the continuous seating of a gas vent control valve on a valve seat even during injection molding operation, as well as acknowledging degradation of performance of the gas venting arrangement.

[0007] These and other objects of the present invention will be attained by providing means for acknowledging an operation mode of a gas venting arrangement in an injection molding apparatus. The molding apparatus is provided with a metal mold formed with a mold cavity and a gas vent passage in fluid communication with the mold cavity, and the gas venting arrangement includes a gas vent control valve movably provided at an exist portion of the gas vent passage for selectively opening and closing the passage, a molten metal detection means provided at the gas vent passage for generating a molten metal detection signal, a control means connected to the molten metal detection means for providing an output drive signal in response to the molten metal detection signal, and a valve driving mechanism connected to the control means and to the gas vent control valve. The valve driving mechanism is operated in response to the output drive signal for moving the gas vent control valve to its valve closing position. The acknowledging means comprises a position sensor provided at a position adjacent the gas vent control valve, the position sensor generating a position detecting signal indicative of a complete closure of the gas vent control valve, a setter in which provisionally settable is a normal period starting from a molten metal detection and ending at a complete closure of the gas vent control valve, a comparator connected to the molten metal detection means and the position sensor for receiving the molten metal detection signal and the position detecting signal for measuring an actual period running from a timing of the molten metal detection by the molten metal detection means to a timing of the position detection by the position sensor, the comparator being also connected to the setter for comparing the actual period with the normal period, and means for generating an alarm when the actual period is outside of the normal period.

[0008] In another aspect of the invention, there is provided a method for acknowledging an operation mode of a gas venting arrangement in an injection molding apparatus, the injection molding apparatus having a metal mold formed with a mold cavity and a gas vent passage in fluid communication with the mold cavity, the gas venting arrangement including a gas vent control valve movably provided at an exist portion of the gas vent passage for selectively opening and closing the passage, a molten metal detection means provided at the gas vent passage for generating a molten metal detection signal, a control means connected to the molten metal detection means for providing an output drive signal in response to the molten metal detection signal, and a valve driving mechanism connected to the control means and to the gas vent control valve, the valve driving mechanism being operated in response to the output drive signal for moving the gas vent control valve to its valve closing position, the method comprising the steps of provisionally setting a normal period starting from the molten metal detection and ending at the complete closure of the gas vent control valve, detecting a closed timing of the gas vent control valve and generating a position detecting signal, measuring an actual period running from the molten metal detection to the position detection, comparing the actual period with the normal period, and generating an alarm if the actual period is outside the normal period.

[0009] These and other objects of this invention will become apparent from the description of the drawings and the preferred embodiments which follow.

[0010] In the drawings;

Fig. 1 is a schematic view showing a die-casting machine provided with a gas venting arrangement and means for acknowledging an operation phase of the gas venting arrangement according to one embodiment of this invention;

Fig. 2 is a vertical cross-sectional view showing a molten metal detection means used in the gas venting arrangement;

Fig. 3 is a schematic cross-sectional view showing a valve driving mechanism in which a modification is made to a valve driving mechanism shown in Fig. 1;

Fig. 4 is a schematic cross-sectional view showing a valve driving mechanism according to another modification; and

Fig. 5 is a schematic view showing an essential portion of a valve driving mechanism in which a modification is made on the embodiment shown in Fig. 4.

[0011] A die casting machine shown in Fig. 1 includes a main die casting section A, a gas venting arrangement B and a means C for acknowledging an operation of the gas venting arrangement B.

[Die-Casting Section A]

[0012] The die-casting section A includes a stationary mold half 1 and a movable mold half 2, and a parting faces 3 are defined therebetween. At the parting faces 3, a mold cavity 4, a gate 16, a runner 16 and a gas vent passage 5 are formed. The gate 16 is positioned immediately upstream the mold cavity 4, and the gas vent passage 5 is positioned downstream the cavity 4. One end of the passage 5 is in fluid communication with the mold cavity 4, and another end is opened to an atmosphere for discharging gas within the cavity 4 to the atmosphere. Alternatively, the other end of the gas vent passage 5 is connected to a vacuum sucking device 15 (described later) for positively discharging the gas within the cavity 4 into the sucking device 15 as shown in Fig. 1. In the stationary mold 1, a casting sleeve 17 extends, and having one end in fluid communication with the runner 16, and another end formed with a casting port 17a through which a molten metal is casted.

[0013] An injection cylinder 18 is provided which is connected to a plunger 19 disposed slidable in the casting sleeve 17. After the molten metal is casted into the casting sleeve 17 through the casting port 17a, and the injection cylinder 18 is actuated, the molten metal is urged toward the mold cavity 4 through the runner 16 and the gate 14. Incidentally, a plunger rod 19a is provided to move the plunger 19. The rod 19a is provided with a striker 20 which is abuttable against limit switches 21, 22. These limit switches 21,22 are connected to a main controller 13. when the striker 20 abuts the first limit switch 21 for injecting the molten metal into the cavity 4, the main controller 13 generates an output signal for actuating the vacuum sucking device 15 (described later), so that gas within the cavity 4 can be discharged. Further, when the striker 20 abuts the second limit switch 22, the main controller 13 generates a second output signal so that advancing speed of the plunger 19 is accelerated for accomplishing high speed casting. In the illustrated embodiment, after the plunger 19 closes the casting port 17a, the striker 20 abuts the first limit switch 21.

[Gas Venting Arrangement B]

[0014] The gas venting arrangement B includes the gas vent passage 5, a molten metal detection means 7, a gas vent control valve 6, a valve driving mechanism 9, a vacuum sucking means 15, a control means 8 and the main controller 13.

[0015] The molten metal detection means 7 is positioned at the gas vent passage 5 so as to detect the molten metal of electrically conductive material. The detection means 7 is electrically connected to the control means 8, and is adapted to generate a signal indicative of the molten metal detection which signal is transmitted to the control means 8. Detailed construction of the detection means 7 is shown in Fig. 2.

[0016] As shown in Fig. 2, the molten metal detection means 7 is fitted in the stationary mold half 1 and is exposed to the gas vent passage 5. The detection means 7 includes a holder 7e fitted in a recessed portion 1a of the stationary mold half 1, and a pair of electrically conductive pins 7a, 7b juxtaposedly supported by the holder 7e through insulators 7c and 7d. Each one ends of the pins project from the insulator 7c and extend into the passage 5 in a direction substantially perpendicular to the molten metal flowing direction. Each another ends of the pins 7a,7b are connected to lines 7g, 7f which are connected to the control means 8 (this connection is shown by a line 24 in Fig. 1). When molten metal is coming into contact with the pins 7a and 7b, an electrical current flows so as to operate the control means 8.

[0017] The gas vent control valve 6 is positioned at an exit end of the gas vent passage 5. The valve 6 is movably provided to open and close the gas vent passage 5, and has a valve head 6a and a valve stem 6c. The valve head 6a can be seated on a valve seat 6b for closing the passage 5. The movement of the gas vent control valve 6 is governed by the valve driving mechanism 9.

[0018] The vacuum sucking device 15 includes an electromagnetic valve 15a connected to the main controller 13, a tank 15b, a vacuum pump 15c and a motor 15d. When the controller 13 sends the first output signal upon abutment of the striker 20 against the first limit switch 21, the electromagnetic valve 15a is shifted to a first position, so that the vacuum is applied to the interior of the gas vent passage 5, the mold cavity 4 and the runner 16 (in a state shown in Fig. 1, the positive gas discharge from the passage 5 is not conducted because of a second position of the electromagnetic valve 15a). The vacuum sucking device 15 can however be dispensed with by providing a gas vent passage with having relatively large diameter. By providing a large volume passage 5, the gas within the cavity 4 and the casting sleeve 17 can be discharged through the gas vent control valve 6.

[0019] Incidentally, if molten metal were to reach the gas vent control valve 6, and discharged therefrom prior to complete seating of the valve head 6a onto the valve seat 6b, in response to the detection of the detection means 7, it would be impossible to conduct subsequent injection molding operation. Therefore, it is necessary to retard the molten material in reaching the valve 6 so that the vent control valve 6 is closed prior to the arrival of the molten material to the valve 6. In this connection, after detection of the molten material by the detection means 7, sufficient time must be provided by delaying the molten material in reaching the valve 6. To this effect, in this embodiment, the gas vent passage 5 is in the form of net pattern having a plurality of obstructing protrusions (not shown) or in the form of meandering pattern (not shown).

[0020] The control means 8 comprises a relay circuit or a switching circuit. Alternatively, an electronic circuit such as a monostable multivibrator and a flip-flop circuit can be used as the control means 8. The control means 8 has one end connected to the detection means 7 by way of a line 24 (actually the lines 7f and 7g). When the molten metal detection signal is inputted from the detection means 7 into the control means 8, the control means 8 generates a drive signal to operate the valve driving mechanism 9 so as to promptly close the gas vent control valve 6, whereby overflow of the molten metal through the control valve 6 is avoidable.

[0021] Next, one example of the valve driving mechanism 9 is shown in Fig. 1. The valve driving mechanism is adapted to operate the gas vent control valve 6, and is operated upon receiving the output drive signal from the control means 8. For this purpose, the valve driving mechanism 9 is connected to the control means 8 by a line 25. The mechanism 9 includes an electromagnetic valve 9c, a valve driving cylinder 9a, a valve driving piston 9b slidably movable within the cylinder 9a, and a pneumatic source or a compressor 9d. The valve driving piston 9b is connected to the valve stem 6c, and divides the cylinder 9a into a front chamber 9i and a rear chamber 9h. At the valve driving cylinder 9a, a position sensor 10 (described later) which is one of the components of the acknowledging means C is provided. The position of the electromagnetic valve 9c is movable to a gas vent control valve closing position and to a gas vent control valve opening position (Fig. 1). When the drive signal is transmitted from the control means 8 to the electromagnetic valve 9c, the latter is moved to the gas vent control valve closing position, so that pneumatic pressure is applied to the front chamber 9i for moving the piston 9b in one direction. Consequently, the gas vent control valve 6 is closed (is moved rightwardly in Fig. 1). On the other hand, when the drive signal from the control means 8 is turned OFF and the electromagnetic valve 9c is moved to the original position, i.e., gas vent control valve opening position (as shown in Fig. 1), the pneumatic pressure from the pneumatic source 9d is applied to the rear chamber 9h to move the piston 9a in opposite direction. As a result, the gas vent control valve 6 is opened. Further, a spring 9g is connected to the electromagnetic valve 9c for moving the latter to its original position by the biasing force of the spring so as to apply compressed air to the rear chamber 9h.

[0022] Another example of a valve driving mechanism 9A is shown in Fig. 3. In the mechanism 9A shown in Fig. 3, a magnetic member 9e is positioned within a space 29 formed in the metal mold 1. The magnetic member 9e is connected to a valve stem 6c, on which a spring 9g is mounted. The spring 9g is adapted to urge the valve head 6a toward its opening direction. An electromagnet 9f is provided in the space and is in confrontation with the magnetic member 9e. Further, a position sensor 10 (one of the elements of the acknowledging means C) is also disposed at the space in confrontation with the magnetic member 9e. When the detection means 7 detects the molten metal and the control means 8 is actuated by the detection signal, an electrical current is applied to the electromagnet 9f for its energization to attract the magnetic member 9e. Consequently, the valve head 6a is seated onto the valve seat 6b against the biasing force of the spring 9g. In this case, the position sensor 10 is accessed by the magnetic member 9e. On the other hand, when the control means 8 is blocked and electrical power supply to the electromagnet 9f is shut off, the magnetic member 9e is moved away from the magnet 9f because of the biasing force of the spring 9g. Consequently, the gas vent control valve 6 is opened.

[0023] Still another example of a valve driving mechanism 9B is shown in Fig. 4 in which provided are two electromagnetic valves 30 and 31 and a pneumatically operated valve 32. Solenoid 30a of the electromagnetic valve 30 is connected to the control means 8, so that the valve 30 is actuated by the output drive signal from the control means 8. The second electromagnetic valve 31 has a solenoid 31a connected to the controller 13 (Fig. 1). The valves 30, 31 have input ports 30b, 31b in communication with a compressor 9d by way of tubes 38, 40 and have output ports 30c, 31c in fluid communication with pilot portions 32a, 32b of the pneumatically operated valve 32 by way of tubes 39, 41. Therefore, change-over operation of the pneumatically operated valve 32 can be made by the selective applications of compressed airs through the pilot portions 32a, 32b. Restoration springs 30d and 31d are connected to the electromagnetic valve 30, 31, respectively for restoring the original positions thereof.

[0024] The pneumatically operated valve 32 has an input port 32c in fluid communication with the compressor 9d by way of a tube 37. Further, output ports 32e and 32f of the pneumatically operated valve 32 are respectively connected, by way of tubes 42 and 43, to a front chamber 9i and a rear chamber 9h of a driving cylinder 9a which drives the gas vent control valve 6. Furthermore, a position sensor 10 (which is a part of the means for acknowledging the operation of the gas venting arrangement) is provided in the rear chamber 9h similar to the foregoing embodiments.

[0025] With the structure, change-over operation of the pneumatically control valve 32 is given by the electromagnetic valves 30 and 31, so that large volume of compressed air can be applied to the front chamber 9i of the cylinder 9a through the pneumatically operated valve 32. Therefore, the gas vent control valve 6 can be promptly closed. More specifically, when the output drive signal from the control means 8 is transmitted into the first electromagnetic valve 30, the valve 30 performs its change-over operation, and therefore, pneumatic pressure is applied to the pilot portion 32a of the pneumatically operated valve 32 by way of the tubes 38 and 39. Accordingly, the pneumatically controlled valve 32 changes its position, so that the large volume of compressed air is supplied into the front chamber 9i through the tubes 37 and 42, to thereby rapidly close the gas vent control valve 6. Upon completion of the injection molding and removal of a flush from the mold cavity 4, the second electromagnetic valve 31 is moved in response to a signal sent from the controller 13. Therefore, compressed air is applied into the pilot portion 32b through the tubes 40 and 41, to thereby change-over the pneumatically operated valve 32. As a result, compressed air is introduced into the rear chamber 9h through the tubes 37 and 43, to thus open the gas vent control valve 6.

[0026] Still another example of a valve driving mechanism 9C is shown in Fig. 5. In this embodiment, the electromagnetic valve 31 in the embodiment shown in Fig. 4 is dispensed with, and instead, a restoration spring 32d is connected to the pneumatically operated valve 32. After the pneumatically operated valve 32 is changed over by the electromagnetic valve 30 in response to the output drive signal from the control means 8, and the output drive signal from the control means 8 is turned OFF after elapse of predetermined period, the pneumatically operated valve 32 is automatically moved to its original position because of the biasing force of the restoration spring 32d. In this embodiment, a position sensor 10 is also provided at a rear chamber 9h of the valve driving cylinder 9a.

[Acknowledging Means C]

[0027] Means C for acknowledging an operation of the gas venting arrangement B will next be described with reference to Fig. 1. The acknowledging means generally includes the position sensor 10, a comparator 12 and a setter 11.

[0028] As described above, the position sensor 10 is provided at a position in confrontation with the gas vent control valve 6 for detecting a close position thereof. The position sensor 10 is adapted to detect the gas vent control valve approaching thereto, and to generate a position detecting signal. In the illustrated embodiment, the position sensor 10 detects a distal end of the piston 9b (Figs. 1, 3 and 5) or the magnetic member 9e (Fig. 3), whose detected position is given when the valve head 6a of the gas vent control valve 6 is completely seated onto the valve seat 6b. The position sensor 10 may be a proximity switch.

[0029] Further, a comparator 12 provided with a pulse counter (not shown) is connected to the position sensor 10 by a line 23, so that the position detecting signal is transmitted to the comparator 12. Moreover, the comparator 12 is also connected to the molten metal detection means 7 by way of a line 26. Therefore, the molten metal detection signal sent from the detection means 7 is also transmitted to the comparator 12. More specifically, when the molten metal detection signal is inputted into the comparator 12, its pulse counter (not shown) starts counting. This count start is made concurrent with the operation start of the electromagnetic valve 9c(Fig.1), 30a (Fig.s 4 and 5) or the electromagnet 9f (Fig. 3) of the valve driving mechanism 9, 9A, 9B,9C. With the arrangement, actual period starting from the molten metal detection timing and ending at the complete closure timing of the gas vent control valve 6 can be measured on a basis of the molten metal detection signal and the position detecting signal those inputted into the comparator 12. This period is hereinafter simply referred to as "actual valve closing period".

[0030] A setter 11 is provided and is connected to the comparator 12 by a line 27. The setter 11 is adapted to set a period running from the molten metal detection by the detection means 7 to the completely closed timing of the gas vent control valve 6. This period is hereinafter simply referred to as a "targeting valve closing period".

[0031] A comparison is made in the comparator 12 between the actual valve closing period and the targeting valve closing period. If the actual valve closing period is within the targeting valve closing period, stability of the gas venting arrangement B can be acknowledged. On the other hand, if the actual valve closing period is outside of the targeting period, an alarm signal D is generated in the comparator. Therefore, any machine trouble or malfunction can be acknowledged.

[0032] The comparator 12 can be connected to the main controller 13 by a line 28 as shown in Fig. 1. In this case, a control signal is transmitted from the comparator 21 to the main controller 13 upon realization of the abnormalities so as to control overall operation of the die casting machine section A.

[0033] Overall operation mode will be described with reference to Fig. 1. Molten metal is casted through the casting port 17a into the casting sleeve 17 while the gas vent control valve 6 is opened. A casting start signal is issued from the main controller 13 to the injection cylinder 18 so as to advance the plunger 19. During movement of the plunger 19, it closes the casting port 17a, and then, the striker 20 abuts the first limit switch 21. As a result of this abutment, the main controller 13 sends the operation signal to the electromagnetic valve 15a of the vacuum sucking device 15. Therefore, gas within the casting sleeve 17 and the mold cavity 4 is discharged out of the metal molds through the gas vent passage 5.

[0034] Further, after the plunger 19 is further moved and the mold cavity 4 is filled with the molten metal, the molten metal may be flowed into the gas vent passage 5. Alternatively, the molten metal may be splashed into the gas vent passage 5 due to high speed injection prior to the complete filling of the molten metal into the cavity 4. In this case, the molten metal detection means 7 detects the molten metal, and sends molten metal detection signal to the pulse counter of the comparator 12 through the line 26 as well as to the control means 8 through the line 24. Upon receipt of the detection signal, the pulse counter starts counting, and simultaneously, the control means 8 sends an output drive signal to the electromagnetic valve 9c (30 in Figs. 4 and 5, or electromagnet 9f in Fig. 3). Therefore, compressed air in the compressor 9d is supplied to the front chamber 9i of the valve driving cylinder 9a. (In Fig. 3, the electromagnet 9f is energized.) Consequently, the piston 9b or the magnetic member 9e is moved together with the valve head 6a, so that the latter will be seated onto the valve seat 6b, whereupon the gas vent passage 5 is closed by the gas vent control valve 6.

[0035] When the gas vent control valve 6 is brought to its close position, the position detector 10 detects the valve 6 (i.e., distal end of the piston 9b or the magnetic member 9e is detected by the sensor 10) and generates the position detecting signal. This position detecting signal is transmitted to the comparator 12 by the line 23, so that the counting in the pulse counter is terminated. That is, measured is the actual period during which the gas vent control valve 6 is closed counting from the molten metal detection by the detection means 7.

[0036] Thereafter, this measured period (actual period) is compared with the targeting valve closing period set in the setter 11, and determination is made as to whether or not the measured period is within the set period. If the actual period is outside the set period, alarm signal D is issued, whereby any abnormality in the gas venting arrangement B is acknowledgeable. In case of this abnormality, a control signal is transmitted to the main controller 13 through the line 28. In response to the control signal, the die-casting section A can also be controlled.

[0037] After the injection molding operation, the movable metal mold half 2 is moved away from the stationary mold half 1 so as to remove the casted product from the mold cavity 4, and at the same time, a flush is removed from the cavity and from the gas vent passage 5. Then, the control means 8 is shut off, and the electromagnetic valve 9c will restore its original position because of the biasing force of the spring 9g (Figs. 1 and 3), or the spring 30d in Fig. 4. As a result, compressed air is applied to the rear chamber 9h for moving the valve head 6a away from the valve seat 6b. In case of the embodiment shown in Fig. 4, the second electromagnetic valve 31 is actuated for applying compressed air to the rear chamber 9h as described above.

[0038] As described above, in the method for acknowledging the operational mode of the gas venting arrangement B according to the present invention, measured is the actual period starting from the molten metal detection timing and ending at the complete seating of the valve head 6a on the seat 6b on a basis of the molten metal detection signal sent from the detection means 7 and the position detecting signal sent from the position sensor 10. And comparison is made in the comparator 12 between the measured period and the set period set in the setter 11, and alarm signal and control signal are transmitted from the comparator if the measured period is outside the set period. Accordingly, in the present invention, various types of abnormalities in the gas venting arrangement B can be promptly acknowledged in such cases where the gas vent control valve 6 maintains its seated position during injection molding, and/or performance of the gas venting arrangement is degraded due to, for example, pressure leakage or reduction in the pneumatic system.

[0039] Further, according to the means for acknowledging the operational mode of the gas venting arrangement of this invention, the above described acknowledgement is performable by a simple construction. Furthermore, by connecting the comparator 12 to the main controller 13, overall operation of the die casting machine section A is controllable. For example, if the measured period is longer than the set period, the advancing speed of the plunger 19 is controlled to be reduced so as to permit the molten metal advancing speed to be lower than the normal speed so as to avoid leakage of the molten metal through the gas vent control valve 6.

Claims

1. Means for acknowledging an operation mode of a gas venting arrangement in an injection molding apparatus having a metal mold formed with a mold cavity and a gas vent passage in fluid communication with the mold cavity, the gas venting arrangement including a gas vent control valve movably provided at an exist portion of the gas vent passage for selectively opening and closing the passage, a molten metal detection means provided at the gas vent passage for generating a molten metal detection signal, a control means connected to the molten metal detection means for providing an output drive signal in response to the molten metal detection signal, and a valve driving mechanism connected to the control means and to the gas vent control valve, the valve driving mechanism being operated in response to the output drive signal for moving the gas vent control valve to its valve closing position, the acknowledging means comprising;
   a position sensor provided at a position adjacent the gas vent control valve, the position sensor generating a position detecting signal indicative of a complete closure of the gas vent control valve;
   a setter in which provisionally settable is a normal period starting from a molten metal detection and ending at a complete closure of the gas vent control valve;
   a comparator connected to the molten metal detection means and the position sensor for receiving the molten metal detection signal and the position detecting signal for measuring an actual period running from a timing of the molten metal detection by the molten metal detection means to a timing of the position detection by the position sensor, the comparator being also connected to the setter for comparing the actual period with the normal period; and
   means for generating an alarm when the actual period is outside of the normal period.

2. The acknowledging means as claimed in claim 1, wherein the injection molding apparatus further comprises a main controller for controlling an overall injection molding operation, and wherein the means for generating the alarm further comprises means for generating and sending a control signal to the main controller when the actual period is outside the normal period for changing injection mode.

3. A method for acknowledging an operation mode of a gas venting arrangement in an injection molding apparatus, the injection molding apparatus having a metal mold formed with a mold cavity and a gas vent passage in fluid communication with the mold cavity, the gas venting arrangement including a gas vent control valve movably provided at an exist portion of the gas vent passage for selectively opening and closing the passage, a molten metal detection means provided at the gas vent passage for generating a molten metal detection signal, a control means connected to the molten metal detection means for providing an output drive signal in response to the molten metal detection signal, and a valve driving mechanism connected to the control means and to the gas vent control valve, the valve driving mechanism being operated in response to the output drive signal for moving the gas vent control valve to its valve closing position, the method comprising the steps of:
   provisionally setting a normal period starting from the molten metal detection and ending at the complete closure of the gas vent control valve;
   detecting a closed timing of the gas vent control valve and generating a position detecting signal;
   measuring an actual period running from the molten metal detection to the position detection;
   comparing the actual period with the normal period; and
   generating an alarm if the actual period is outside the normal period.

4. The method as claimed in claim 3, wherein the injection molding apparatus further comprises a main controller for controlling an overall injection molding operation, and wherein the method further comprises the step of generating a control signal and sending the control signal to the main controller for changing the injection mode.

Drawing