JPS6151968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for evacuation of a mold used in injection molding, in which air and the like in the mold cavity are exhausted and then the cavity is filled with molten resin.

Preventing air from getting into molded products during high-speed injection molding, removing water droplets from insert parts during insert molding, and removing air in the mold cavity after clamping for precision molding with sharp parts. A method is adopted in which the molten resin is filled after discharging the molten resin.

Conventionally, as seen in Japanese Patent Publication No. 55-19734 shown in Fig. 1, an on-off valve 4 was installed in a cavity 3 formed by a fixed mold 1 and a movable mold 2 during injection molding.
A vacuum pump 6 was attached to the pipe 5 to exhaust air and the like from the cavity 3. Therefore, when increasing the molding cycle, the air inside the cavity 3 must be evacuated quickly, sometimes instantaneously, which requires a relatively large-capacity vacuum pump, which is expensive.

In addition, when opening the mold after molding, there may be negative pressure inside the cavity, so the mold may not open smoothly, or the pressure holding process after filling may be started due to an interlock failure. However, there were problems such as continuous vacuuming.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method for evacuation of a mold that is inexpensive, efficient, and stable and eliminates the above-mentioned drawbacks.

Next, one embodiment of the present invention will be explained with reference to FIGS. 2 and 3. 10 is a movable die plate;
The cavity 12 is formed by a mold in which male and female molds 11a and 11b come into contact when the molds are clamped. Reference numeral 13 denotes an exhaust pipe for removing air, etc. from inside the cavity, and it communicates with a vacuum pump 15 driven by the drive motor 14. The exhaust pipe 13 is provided with a tank 16 having an opening 16a communicating with the cavity side and 16b communicating with the vacuum pump side, and electromagnetic switching valves 17 and 18 for opening and closing the respective openings 16a and 16b are provided. .

19 is a pressure switch that detects the pressure inside the tank 16 and issues a signal. Further, a branch pipe 20 that is open to the atmosphere is provided between the cavity 12 of the exhaust pipe 13 and the cavity-side electromagnetic switching valve 17, and an electromagnetic switching valve 21 that controls opening and closing of the branch pipe 20. is provided.

Also, to explain the expanded connection diagram in Figure 3,
31 is a relay for controlling the drive motor 14 of the vacuum pump 15, and has an A contact 31a, and when the contact 31a is connected, the vacuum pump drive motor 14 is driven. Reference numeral 32 denotes a solenoid for the electromagnetic switching valve 18, which is energized simultaneously with the operation of the relay 31. Reference numeral 33 denotes a changeover switch, which switches the circuit so that the vacuum evacuation device according to the present invention operates automatically, and has A contacts 33a ₁ and 33a ₃ . 3
4 is a vacuum completion relay that controls whether or not the vacuum in the tank 16 has been completed; A contact 34a,
34a ₃ and B contact 34b ₂ . Reference numeral 35 denotes a vacuum timer, which has A contacts 1TR ₁ and 1TR _{3 and} B contacts 1TR ₂ , and communicates the inside of the tank 16 with the cavity 12, so that air, etc. in the cavity 12 is transferred to the tank 16.
The timer 38 for setting the time for the injection operation is operated. Reference numeral 36 is a relay for pulling vacuum from the mold and has an A contact 36a. Reference numeral 37 denotes a relenoid of the electromagnetic valve 17, which is excited when the mold is evacuated. 39
is a vacuum timer and is the same timer 3 as the timer 35 above.
9, the inside of the mold cavity 12 is evacuated for a set period of time. Here, the vacuum evacuation time was set separately for the timers 35 and 39, but of course one timer is sufficient, and in this embodiment, it was used as a start signal for the timer 38 for the injection operation. Each of the timers 38 and 39 has contacts 2TR ₁ and 3TR ₁ , respectively. 40 is a pressure increase relay that controls whether the pressure in the mold clamping cylinder has increased to a predetermined pressure; 41 is a timer that sets a chiring timer and has a contact 4TR.

The control circuit is as described above, and its operation will be explained next. First, the switch 33 is turned on so that the vacuum inside the mold is automatically performed.
When the solenoid 32 of the electromagnetic switching valve 18 is energized, the pipe line of the electromagnetic switching valve 18 is switched to the vacuum pump 15.
At the same time, the relay 31 of the motor 14 for driving the vacuum pump 15 starts operating, and the A contact 3
1a is connected, and the motor 14 starts driving.
When air or the like is suctioned from inside the tank 16 and the inside of the tank 16 reaches a predetermined pressure, the pressure switch 19 detects this and issues a signal to activate the vacuum completion relay 3.
4 starts operating, a vacuum operation relay 36 (described later) is also operating, and the vacuum completion relay 34 is self-held. On the other hand, the mold clamping lift has been completed, the movable die plate 10 has been moved to the forward limit, and the limit switch LS2 in the pressure increase circuit is activated.
is connected, and the pressure increase relay 40 is also activated. The timer 35 starts counting by the operation of the pressure switch 19 mentioned above, and the A contact _1TR1 is connected, so that the timer 35 is self-maintained. At the same time, A contact 1TR ₃ is also connected, and the electromagnetic switching valve 17 is energized.
Since the pipeline is opened, cavity 12 and tank 16
are in communication with each other, and the air etc. in cavity 12 is communicated with tank 1.
When a predetermined period of time elapses during which the relay 36 is activated, the A contacts 1TR ₁ and 1TR ₃ are opened, the B contact 1TR ₂ is connected, and the timer is activated. 39 and 38 start operating. The vacuuming operation continues even after the timer 35 expires, the A contact of the timer 39 2TR ₁
The circuit is maintained, so it can continue as it is,
Eventually, the process continues for the time set in the timers 35 and 39. When the evacuation operation is completed, that is, when the timer 39 counts out, the evacuation operation relay 36 is turned off, and at the same time, the vacuum completion relay 64 is also turned off, so the B contact 34b ₂ in the circuit of the vacuum pump 31 is turned on, and the vacuum pump 14 is turned off. Driving is started and suction in the tank 16 is performed again.

On the other hand, when the time set in the injection operation time 38 activated by the time-out signal of the timer 35 times out, the A contact 3TR ₁ is connected, and the carrying timer 41 performs metering and cooling.
starts operating, its A contact _4TR1 is connected and the relay 41 is self-holding, and the B contact is activated by the timeout signal of the carrying timer relay 41.
4TR ₂ enters and the solenoid 42 of the electromagnetic switching valve 21 is energized, so the pipe line 20 is opened and the cavity 1
2 is in communication with the atmosphere, eliminating the conventional disadvantage of creating a negative pressure inside the cavity for die retraction when the mold is opened.In this way, the inside of the cavity is opened to the atmosphere when the mold is opened by a timeout signal of the carrying time. Therefore, the movable die plate 10 can be smoothly retreated when opening the mold, and the filling process is completed because the vacuum operation circuit is provided with the B contact 43b of the filling process completion relay (not shown) during the injection operation. In other words, after the relay is activated, it does not operate, and an interlock is provided so that the evacuation operation is completed before the filling process is completed. Therefore, a vacuum operation is performed during injection to prevent resin from entering the suction hole.

As explained above, the method of the present invention can significantly reduce the cost compared to the conventional apparatus, and since the mold opening/closing operation can be performed reliably, the molding operation can be performed stably.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional method. FIG. 2 is a diagram showing one embodiment according to the present invention. FIG. 3 is a diagram showing a control circuit according to the present invention. 11... Mold, 12... Cavity, 13...
Exhaust pipe line, 15... Vacuum pump, 16... Tank, 17, 18, 20... Solenoid valve, 19... Pressure switch.

Claims (1)

[Scope of Claims] 1. In a mold vacuum evacuation method used in vacuum injection molding, in which air, etc. in the cavity is exhausted after the mold clamping process is completed, and molten resin is injected into the cavity, A tank that communicates with the vacuum pump is provided in the exhaust pipe line for exhausting air, and an electromagnetic switching valve that opens and closes the pipe is provided in each of the exhaust pipe lines that communicate with the cavity side port of the tank and the vacuum pump side port. Additionally, a branch pipe communicating with atmospheric pressure via another electromagnetic switching valve for opening/closing the pipe is provided between the cavity and the electromagnetic switching valve, and the cavity side pipe of the tank is evacuated in advance by the vacuum pump before evacuation. is opened, vacuum is drawn from the cavity, and after the vacuum is completed, the cavity side pipe is closed, and a branch pipe communicating with the atmosphere is opened to allow the atmosphere to act on the cavity. Mold vacuuming method. 2. The mold evacuation method according to claim 1, wherein the evacuation from the mold cavity is completed before a filling step in an injection step is completed. 3. When opening the mold to take out the product molded in the mold cavity, the branch pipe communicating with the atmospheric pressure is opened to the atmosphere when the mold clamping pressure is lowered and the mold is opened at low speed. A mold evacuation method according to claims 1 and 2.