JPH0646656Y2 - Shock prevention hydraulic circuit of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a hydraulic circuit of an injection device in a plastic injection molding machine. More specifically, after the injection process is completed,
The present invention relates to a shock-preventing hydraulic circuit for mitigating a shock generated when a screw back pressure process is performed.

[Prior Art] An injection device has a function of injecting and filling a fixed amount of a resin, which has been plasticized by being given heat, into a mold that has been clamped. As an injection device of this type, an in-line screw type, which employs a feed screw built-in injection cylinder, is mainly used. FIG. 2 shows a configuration example of a conventional hydraulic circuit of an in-line screw type injection device.

In the figure, in the injection cylinder indicated as a whole by reference numeral 1,
The outer cylinder 1a is configured as a part of a heating cylinder including a band heater (not shown) for heating a raw material (resin).
On the other hand, the piston 1b inside the outer cylinder 1 moves forward to the injection side (y ₁ direction in FIG. 2) by hydraulically driving, and injects the resin heated and melted inside the heating cylinder into the mold ( Injection process)
Do. Further, the screw (not shown) connected to the rod 1c of the piston 1b is rotated in the y ₂ direction shown in the drawing while being rotated by the drive of a hydraulic motor (hydraulic drive device) not shown in the screw back pressure process following the injection process.
Retreat with 1b. Further, by the rotation of the screw, the resin to be used in the next injection step is taken into the heating cylinder from the hopper (not shown). In this case, the pressure increase due to the heating and melting of the resin is appropriately controlled by the screw back pressure operation. The hydraulic motor is adapted to be supplied with working pressure oil from the B port of the electromagnetic pilot direction switching valve 2 which switches between the injection operation and the screw back pressure operation.

Each step of the injection cylinder 1 will be described together with the hydraulic circuit shown in FIG.

I. Injection Process First, when the solenoid 2a of the electromagnetic pilot direction switching valve 2 is excited, the injection process is performed. That is, the pressure oil from the pressure oil supply source 3 is introduced into the injection cylinder 1 through the P port to the A port of the switching valve 2, and the injection pressure is applied to the rod side of the piston 1b to advance it in the y ₁ direction to cause the above-mentioned change. Injection operation is performed. In this case, the maximum pressure of the injection line 4 is higher than the set pressure of the relief valve by giving the pressure oil discharged from the pilot vent port of the switching valve 2 to the pilot relief valve 6 in reverse to kill the main relief valve 5. For example, the pressure is controlled to about 140 kg / cm ^2. II. Screw back pressure step Next, the solenoid 2a is demagnetized, and the solenoid 2b is excited to drive the hydraulic motor. Demagnetization of the solenoid 2a causes the switching valve 2 to start switching to the neutral position, and at the same time, the pressure in the pilot vent port decreases, which causes the pilot relief valve 6 to start functioning, but the main relief valve 5 operates as follows. Due to this rapid decrease in pressure in the vent port, the pressure in the injection line 4 is instantaneously reduced to almost the tank pressure, and then the set pressure of the pilot relief valve 6 is restored to maintain a predetermined back pressure of, for example, 10 kg / cm ^2. To be done.

In this case, the pressure of the molten resin acts on the piston 1b to apply an external force in the y ₂ direction, and this pressure is controlled by the main relief valve 5 as described below.

That is, when the switching valve 2 is switched, the pilot relief valve 6
The vent port of the main relief valve 5 is opened via, and the main relief valve 5 is set to a set pressure, so that a hydraulic resistance (screw back pressure) against the resin pressure is generated in the line 4. Here, the screw back pressure, that is, the set pressure of the pilot relief valve 6 with respect to the main relief valve 5 is appropriately determined according to the type of resin and the injection amount. In this way, the screw back pressure process is performed by rotating the screw and retracting the piston 1b while applying the screw back pressure.

[Problems to be Solved by the Invention] In the conventional hydraulic circuit as described above, the pressure in the injection line 4 at the time of shifting to the screw back pressure process after the injection process is almost equal to that of the tank 7 just before the screw back pressure occurs. The pressure drops to about. That is, the pressure in the y ₁ direction with respect to the piston 1b is not accompanied by an undershoot when the injection pressure shifts to the screw back pressure. The shock resulting from this has the inconvenience of causing noise or mechanical vibration of the injection device.

The present invention has been made in view of such problems, and an object thereof is to smoothly perform pressure switching from the injection pressure of the injection line to the screw back pressure without undershoot. It is an object of the present invention to provide a shock-preventing hydraulic circuit of an injection molding machine that can prevent the occurrence of shock.

[Means for Solving the Problems] In order to achieve the above object, in a shock-preventing hydraulic circuit of an injection molding machine of the present invention, an injection cylinder for injecting a heated and melted resin into an injection molding die, An electromagnetic pilot that is connected to the injection piston of the cylinder and that reverses the piston in the direction opposite to the injection side, and an electromagnetic pilot that switches the direction of the pressure oil between the injection operation of the injection piston and the screw back pressure control operation when the piston is retracted. Directional switching valve and A of the switching valve
An injection line connecting the port and the cylinder, a hydraulic drive device connected to the B port of the switching valve and for retracting the screw, and a pressure oil supply source connected to the P port of the switching valve. A main relief valve that is connected to the injection line and opens the injection pressure to the tank when the pressure oil pressure for injection exceeds a predetermined pressure; and a vent port of the main relief valve. And a pilot relief valve connected to the main relief valve, the flow path connecting the vent port of the main relief valve and the pilot relief valve is discharged from the pilot vent port of the switching valve during the injection operation. It closes against the spring with oil, and at the end of the injection operation, the communication opening of the connection flow path is gradually increased due to the pressure drop in the pilot vent port. A pilot shutoff valve that is opened by the spring is added.

[Operation] According to the above configuration, the pressure oil is supplied from the main relief valve to the pilot relief valve through the pilot shutoff valve. This pilot shut-off valve moves from the closed state to the open state by the spring force accompanying the pressure drop of the pilot vent port of the electromagnetic pilot direction switching valve, but at that time it does not open momentarily but gradually. It is supposed to open. That is, the response of the pilot relief valve to the main relief valve immediately after the injection process is
It is being held gradually. Here, by appropriately setting the degree to which the pilot shutoff valve gradually opens, the pressure in the injection line after the injection process can be smoothly transferred to the screw back pressure without undershoot. Becomes

To further clarify the features and advantages of the present invention, a preferred embodiment will be described with reference to the accompanying drawings.

[Embodiment] FIG. 1 shows the configuration of a shock-preventing hydraulic circuit according to an embodiment of the present invention.

In FIG. 1, the components denoted by the same reference numerals as those in the conventional circuit of FIG.

The main difference between the shock-preventing hydraulic circuit of the present invention and the conventional circuit of FIG. 2 is that a pilot shutoff valve 8 is provided in the pilot line of the main relief valve 5. The operation of the shock-preventing hydraulic circuit according to the present invention will be described below, focusing on the shutoff valve 8. The operation of the piston 1b associated with the switching of the electromagnetic pilot direction switching valve 2 is the same as the steps I and II of the above-mentioned conventional technique.

The shut-off valve 8 has its pilot port 8p connected to the pilot vent port of the switching valve 2. However, when no pressure is applied to this pilot port 8p, a spring is used.
The inlet 8i and the outlet 8o are connected at the previous opening by the spring force of 8s.

On the other hand, from the pilot vent port of the switching valve 2 to the pilot port 8p accompanying the injection drive of the piston 1b during the injection process.
When a pressure higher than the pressure set by the spring 8s is applied to the spring, the spool (not shown) of the shutoff valve 8 moves against the spring 8s, and the opening degree between the inlet 8i and the outlet 8o gradually decreases. And finally the connection is cut off.

Next, when the injection process is completed and the pressure in the pilot port is released, the spool is moved to the original position (the inlet 8i by the spring 8s).
~ Return to the position where the exit 8o was opened. The flow passage opening / closing control portion of the spool is provided with a processing portion such as a predetermined inching, so that the communication opening degree of the flow passage with respect to the stroke of the spool is gradually changed. Therefore, when shifting to the screw back pressure process after the completion of the injection process, the main relief valve 5 does not excessively reduce the pressure of the injection line 4 to the tank pressure. Therefore, the pressure of the injection line 4 can be transferred from the injection pressure to the screw back pressure without undershoot, and thus the shock is prevented.

[Effect of the Invention] As described above, according to the shock-preventing hydraulic circuit of the injection molding machine of the present invention, it is possible to shift from the injection process to the screw back pressure process without a shock. Therefore, there is an effect that noise and mechanical vibration of the molding machine during the transition can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a configuration of a shock prevention hydraulic circuit of an injection molding machine according to an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram showing a configuration example of a hydraulic circuit of a conventional injection molding machine. . [Description of symbols of main parts] 1 ... Injection cylinder 2 ... Electromagnetic pilot direction switching valve 3 ... Pressure oil supply source 4 ... Injection line 5 ... Main relief valve 6 ... Pilot relief valve 7 ... Tank 8 ...... Pilot shutoff valve

Claims (1)

[Scope of utility model registration request] 1. An injection cylinder for injecting a heat-melted resin into an injection molding die, a screw connected to an injection piston of the cylinder and for retracting the piston in a direction opposite to the injection side, and the injection. Solenoid pilot direction switching valve for switching the direction of pressure oil between the injection operation of the working piston and the screw back pressure control operation at the time of retraction, the injection line connecting the A port of the switching valve and the cylinder, and the switching valve A hydraulic drive device connected to the B port and for moving the screw backward, a pressure oil supply source connected to the P port of the switching valve, and the injection line,
A main relief valve for releasing the injection pressure to the tank when the injection pressure oil pressure exceeds a predetermined pressure; and a pilot relief valve connected to a vent port of the main relief valve. In the above, the connection flow path between the vent port of the main relief valve and the pilot relief valve is closed against the spring by the pressure oil discharged from the pilot vent port of the switching valve during the injection operation, At the end of the injection operation, a shock of the injection molding machine, which has a pilot shut-off valve opened by the spring so as to gradually increase the communication opening degree of the connection flow path due to the pressure drop of the pilot vent port. Prevent hydraulic circuit.