JPH0785906B2 - Method of shortening injection start time in injection speed control - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for shortening the injection start-up time in injection molding of a hydraulically operated injection cylinder.

[0002]

2. Description of the Related Art In a conventional injection hydraulic circuit shown in FIG. 4, a hydraulic circuit of an oil pump PV and an injection cylinder 1 having a variable discharge amount is used to supply and discharge oil in a retreat side oil chamber 3 partitioned by a piston 2. A direction switching valve V1 that discharges oil from the forward oil chamber 4 and a direction switching valve V2 that supplies oil to the forward oil chamber 4 and the oil motor M are provided.

Further, in the conventional injection hydraulic circuit of FIG. 5, an oil pump PF having a constant discharge amount is used in place of the variable oil pump PV, and the discharge amount is controlled by a hydraulic path between the directional control valve V2. This is performed by a proportional valve V3 provided and a relief valve V4 provided over the hydraulic path and the return circuit of the oil motor.

In any of the prior arts, the directional switching valve V1 and the directional switching valve V2 are simultaneously switched from the illustrated state to the b side and the a side, respectively, at the start of injection. And the forward hydraulic path is blocked. In the directional control valve V2, the pump side hydraulic passage and the forward side hydraulic passage are connected, oil acts on the forward side oil chamber 4, and the piston moves forward while discharging the oil in the backward side oil chamber 3. Injection is started.

[0005]

In the injection hydraulic circuit shown in FIG. 4, the flow rate and pressure of the oil pump PV rise simultaneously with the switching operation of the directional control valves V1 and V2 of the 4-way valve, and the piston 2 moves forward. However, the start of the movement of the piston 2 is greatly affected by the rising of the oil pump PV, and it is difficult to promptly advance the injection.

In the injection hydraulic circuit shown in FIG. 5, after the oil pump PF is operated, the directional control valves V1 and V2 are simultaneously operated together with the proportional valve V3.
Due to the slight switching delay of No. 3 and the inertial force of oil after the proportional valve, the injection advance is likely to be delayed.

The present invention has been conceived in order to solve the above-mentioned conventional problems, and its purpose is to make a rise time at the start of injection by slightly changing the conventional injection hydraulic circuit and a new operating means. It is to provide a method that enables shortening of.

[0008]

SUMMARY OF THE INVENTION The features of the present invention according to the above-mentioned object are to switch the direction in which the oil in the reverse side oil chamber is supplied to and discharged from and the oil in the forward side oil chamber is discharged from the hydraulic passage of the oil pump and the injection cylinder. A valve V1 and a directional switching valve V2 for supplying oil to the forward oil chamber are provided, and the backward hydraulic passage chamber is blocked by the directional valve V1 to connect the forward hydraulic passage to the tank side. Then, by switching the direction switching valve V2, the oil from the oil pump is caused to act on the forward oil chamber, and the direction switching valve V1 bleeds off to the tank.
After that, the direction switching valve V1 is switched to connect the backward hydraulic passage to the tank side and block the forward hydraulic passage to start injection.

[0009]

[Operation] In the above method, when the direction switching valve V2 is switched to start injection and oil is supplied from the oil pump to the forward hydraulic passage, only a part of the oil acts on the forward oil chamber, Most of the oil bleeds off from the directional control valve V1 to the tank. During this time, the oil flow rate rises to a predetermined value, so switching of the directional control valve V1 stops the bleed off of the oil, and the reverse side hydraulic path is closed. When the oil resistance is removed, the piston 2 moves forward rapidly.

[0010]

1 and 2 show an embodiment of the present invention. The same parts as those of the conventional injection hydraulic circuit shown in FIGS. 4 and 5 will be described with the same reference numerals. Further, the difference between the embodiment and the conventional injection hydraulic circuit is that the port at the neutral position of the directional control valve V1 is partially different, and the other configurations are exactly the same. Therefore, the description of the injection hydraulic circuit is omitted.

The difference of the directional control valve V1 is that FIG. 4 and FIG.
The conventional directional control valve V1 shown in FIG. 2 has a structure in which both the backward hydraulic passage and the forward hydraulic passage are connected to the tank side, whereas in this embodiment, the backward hydraulic passage is blocked and the forward hydraulic passage is blocked. Is connected to the tank side. Therefore, in the embodiment, even if the oil acts on the forward-side oil chamber before the start of injection, the piston does not move forward and is in a stopped state.

In the embodiment shown in FIG. 1, the directional control valve V2 is used to start injection from the state in which the piston 2 is retracted and stopped.
Is switched to the side a, the ports P and A are connected, and when oil is supplied from the oil pump PV to the forward hydraulic passage, a part of the oil acts on the forward oil chamber 4, and most of the other oil is directional. Bleed off to the tank by connecting the ports B and T of the switching valve V1.

In the oil pump PV whose discharge amount is variable,
Although the swash plate acts to discharge the flow rate, there is operating loss time for the swash plate, but the loss time disappears during bleed-off, and the discharge amount rises to the set value, so the direction is changed when the timing is checked. When the valve V1 is switched to the b side and the port A is blocked to the tank side and the port B is blocked to stop the oil bleed-off, all the oil in the forward hydraulic passage immediately acts on the forward hydraulic chamber 4 to cause the piston 2 to move. Move forward quickly.

After the injection is completed, the directional control valves V1 and V2 are simultaneously switched to the a side and the b side, the ports A and P are connected to supply oil to the reverse hydraulic passage, and the ports A and T are connected. The piston 2 moves backward and stops while discharging the oil in the forward oil chamber 4 to a fixed position by the oil acting on the backward oil chamber 3, and stands by at that position.

In the embodiment shown in FIG. 2, the bleed-off is performed by first switching the directional switching valves V1 and V2 without switching the proportional valve 3 and the directional switching valves V1 and V2 after bleeding off with the relief V4. As a result, the flow from the oil pump overcomes the inertial force of the oil from the proportional valve V3 to the injection cylinder 1, so that the delay in injection rise is eliminated.

FIG. 3 shows the injection start-up state in the case of the above embodiment, and FIG. 6 shows the injection start-up state in the conventional case. As is clear from the comparison of both, the injection start-up (right side of the figure). (See) is more remarkable than in the past.

[0017]

As described above, the present invention supplies oil from the oil pump to the hydraulic passage on the forward side during injection, causes the oil to act on the oil chamber on the forward side, bleeds off to the tank, and then reverses by switching. Since the side hydraulic passage is connected to the tank side and the forward hydraulic passage is blocked to start injection, the following effects are achieved.

Even if the swash plate of the variable discharge pump has an operation loss time, the oil acts on the forward-side oil chamber of the injection cylinder due to bleed-off, so switching causes the piston to move in a shorter time than before. The injection speed can be raised to the set speed.

In molding with a short injection stroke, the injection stroke tends to reach the end before the set speed is reached, depending on the rising response of the swash plate, but the injection amount is small because the injection speed rises to the set speed in a short time. But you can get good products.

In the case of an oil pump using a proportional valve, the injection speed is not affected by the switching response of the proportional valve, and is not affected by the inertial force of the oil between the proportional valve and the injection cylinder. Can be raised in a short time.

The bleed-off improves the flow rate response due to the inertia and viscosity of the oil in the hydraulic line and reduces the flow resistance, so that the rise time is shortened also from this point.

[Brief description of drawings]

FIG. 1 is an injection hydraulic circuit diagram of an embodiment of the method of the present invention.

FIG. 2 is a injection hydraulic circuit diagram of another embodiment of the present invention.

FIG. 3 is a diagram showing an injection rising state in the case of the present invention.

FIG. 4 is an injection hydraulic circuit diagram according to a conventional method.

FIG. 5 is an injection hydraulic circuit diagram according to another conventional method.

FIG. 6 is a diagram showing a rising state of injection in a conventional case.

[Explanation of symbols]

 1 Injection cylinder 2 Piston 3 Reverse side oil chamber 4 Forward side oil chamber V1 Directional switching valve V2 Directional switching valve V3 Proportional valve V4 Relief PV Oil pump (variable discharge rate) PF Oil pump (quantity)

Claims (1)

[Claims] 1. A direction switching valve V1 for supplying / discharging oil to / from the reverse side oil chamber and discharging oil to / from the forward side oil chamber, and supplying oil to the forward side oil chamber, to a hydraulic passage of an oil pump and an injection cylinder. The directional control valve V1 is provided with the directional control valve V2.
In the state in which the reverse hydraulic passage chamber is blocked by and the forward hydraulic passage is connected to the tank side, the oil from the oil pump is caused to act on the forward hydraulic chamber by switching the direction switching valve V2, and Bleed off from V1 to the tank, and then switch the directional control valve V1 to connect the reverse hydraulic passage to the tank side and block the forward hydraulic passage to start injection. How to shorten the rise time.