JP2769648B2

JP2769648B2 - Injection molding machine

Info

Publication number: JP2769648B2
Application number: JP3072414A
Authority: JP
Inventors: 良三盛田
Original assignee: 株式会社名機製作所
Priority date: 1991-03-12
Filing date: 1991-03-12
Publication date: 1998-06-25
Anticipated expiration: 2011-03-12
Also published as: JPH04284221A

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine having a backflow prevention ring disposed between a screw body and a screw head of an injection device.

[0002]

2. Description of the Related Art In a screw of an injection molding machine, a backflow prevention ring is provided between a screw body and a screw head in order to prevent molten resin extruded toward a nozzle from moving toward the screw body during operation of an injection process. Have been. When the molten resin is transferred forward into the screw groove by the rotation of the screw, the ring is pushed by the molten resin, moves toward the screw head, and contacts the rear end face of the head. For this reason, the molten resin passes through the through hole of the backflow prevention ring from the screw groove, and accumulates in the space in front of the screw head through the notch at the screw head side end. When the metering process is completed, the screw moves forward to inject the accumulated molten resin, the ring moves relatively to the retracted position, moves from the screw head side toward the screw body, and the screw body is compressed by the action of the molten resin. Pushed back by the molten resin flowing backward, the retreating surface of the ring comes into contact with the end face of the screw body, and the inner flow passage of the ring is closed.

[0003] However, the closing operation speed of the backflow prevention ring differs depending on the properties of the accumulated molten resin, and fluctuations in the operating speed make it impossible to equalize the amount of resin injected into the mold.

For this reason, according to Japanese Patent Publication No. 59-47979, a screw head is provided with a lead screw in the same direction as the screw head body, so that the screw is measured only for a short time after the completion of the measuring process or immediately before the start of the injection process. A method is disclosed in which by rotating the resin in a direction opposite to the rotation direction and closing the backflow prevention ring in advance by the backflow of the resin, the measured resin in front of the screw at the start of the injection process can be surely filled into the mold without backflow. Have been.

[0005] In this case, however, since a lead screw is provided on the screw head in the same manner as the screw body, a head having a new dimension and shape must be specially ordered.

Further, there is a conventional method in which a molten resin is filled into a space in front of a screw and then sucked back. In this case, since the resin at the rear side of the ring valve is sent forward by sucking back, there is a drawback that the resin is filled more than the amount of the resin at the time when the filling of the resin into the gap is completed.

[0007]

SUMMARY OF THE INVENTION In view of such circumstances, it is an object of the present invention to improve the closing of a ring valve, to eliminate the backflow of resin from the ring valve during injection, and to reduce the variation in injection amount. It is to provide an injection molding machine.

[0008]

In order to achieve the above object, an injection molding machine according to the present invention is provided with a screw which is inserted into a heating cylinder so as to move forward and backward and is rotatable, and the screw is provided on the inner wall of the heating cylinder. A ring valve that slides and is loosely fitted to the small diameter portion between the screw head and the screw body is arranged, and a screw position detector for confirming the weighing completion position; and the screw based on a confirmation signal from the position detector. And a controller for stopping the rotation when the torque of the rotating screw reaches a predetermined set value.

[0009]

According to this configuration, after the weighing process is completed by rotating the screw, when the screw rotates in the opposite direction to the weighing process,
Since the molten resin behind the ring valve is sent backward,
Since a pressure difference is generated between the front side and the rear side of the ring valve, the ring valve retreats toward the screw body and closes the valve.

When the screw torque reaches a predetermined set value, that is, when the ring valve is completely closed and the forming conditions are not disturbed, the screw is driven to rotate in the reverse direction.

[0011]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view of a main part of an injection molding machine according to the present invention, FIG. 2 is a block diagram of a main part of a control device, and FIG. 3 is a flowchart.

In FIG. 1, reference numeral 1 denotes a heating cylinder for plasticizing a resin falling from a hopper (not shown) using a screw 2. A cylinder head 4 having a nozzle 3 that comes into contact with a sprue bush of a mold is attached to a distal end portion of the heating cylinder 1. A conical space 6 is provided behind the nozzle in conformity with the tip shape of the screw head 5, and communicates with a through hole 7 through which the screw 2 moves forward and backward in the heating cylinder 1.

The screw 2 comprises a screw body 8 having a lead screw 2a for transferring the resin dropped from the hopper to the nozzle 3 while melting and kneading the resin, and a screw head 5 connected to the tip of the screw body. 8 and head 5
A connecting portion of the screw head 5 has a small diameter portion, and a ring valve 9 for preventing backflow of the molten resin is movably inserted between the rear end face B of the screw head 5 and the front end face C of the screw body 8.

The ring valve 9 is in sliding contact with the inner wall of the through-hole in the heating cylinder 1. Further, a notch 11 is provided at the tip of the ring valve 9 or at the screw head 5 side, and the small-diameter rear end 5 a of the screw head 5 is connected to the ring valve 9. Between the screw head 5 and the screw resin 5 so that the molten resin flows into the space 6 on the front side of the screw head due to the gap between them.
Is formed.

The rear end of the screw 2 is connected to an oil motor 20 shown in FIG. 2 via a bearing box (not shown). In FIG. 2, reference numeral 21 denotes an electromagnetic direction switching valve, which can supply hydraulic oil so that the oil motor 20 rotates forward when the solenoid S1 is excited, and rotates reversely when the solenoid S2 is excited. Reference numeral 22 denotes an electromagnetic relief valve that adjusts the pressure of hydraulic oil supplied to the oil motor 20. Reference numeral 23 denotes a pressure sensor which outputs an electric signal corresponding to the pressure of the working oil supplied to the oil motor 20. Reference numeral 25 denotes a screw position detector.

Reference numeral 30 denotes a main controller of the injection molding machine, 31 is a CPU of the controller 30, 32 is an input / output unit, 33 is a memory, 34
Denotes an operation unit.

The essential points of the operation of the injection molding machine having the above configuration will be described with reference to the flowchart of FIG.

Prior to injection, a weighing process for storing a predetermined amount of molten raw material in the gap 6 is started. That is, the CP receiving the measurement process start signal from the input / output unit 32
U31 transmits the Kudo maximum oil pressure of the oil motor 20 set and stored by the operator in the memory 33 in advance to the input / output unit 32.
The input / output unit 32 is connected to the driving maximum hydraulic pressure, for example, 175 kg / cm ²
Is output to the electromagnetic relief valve 22. At the same time, the solenoid S1 of the electromagnetic directional control valve 21 is excited.

As a result, the hydraulic oil supplied from the hydraulic pressure source is supplied to the oil motor 20 through the electromagnetic directional control valve 21 while the maximum pressure is regulated to, for example, 175 kg / cm ² , and the oil motor 20 The screw 2 rotates forward. The raw material supplied from a hopper (not shown) is transferred forward while plasticizing inside the heating cylinder 1 by the rotation of the screw 2. When the screw 2 retreats by the amount of the plasticized raw material transferred to the gap 6 and reaches the preset measurement completion position, the input / output unit 32 completes the measurement based on the detection signal of the screw position detector 25. Issue a command. The solenoid S1 of the electromagnetic direction switching valve 21 and the electromagnetic relief 22 are demagnetized, and the rotation of the oil motor 20 stops.

During this measuring step, the pressure P1 actually supplied to the oil motor 20 is detected by the pressure sensor 23,
It is stored in the memory 33 of the main controller 30. That is, in the present embodiment, the torque of the screw 2 is easily grasped in the form of an actually measured value of the hydraulic pressure supplied to the oil motor 20 without requiring a complicated mechanism.

When the measurement process is completed, the product P2 of the pressures P1 and k stored in the memory 33 is calculated in the CPU 31 instantaneously. Here, k is a numerical value of 1 or less, usually about 0.2 to 0.3.

It is assumed that k is 0.3 and stored in the memory 33. If P1 is 100 kg / cm ² , then P2 = P1 × k = 100 × 0.3 = 30 kg / cm ² .

When the measurement process is completed and P2 is calculated, prior to the injection process, the solenoid S2 of the electromagnetic directional control valve 21 is energized to reversely rotate the screw 2 in order to close the ring valve 9 securely. Is performed. Pressure sensor 23
Supply oil pressure P of oil motor 20 detected by main controller 30
And the magnitude of P and P2 is continuously compared and calculated. And P is P2, here 30
When kg / cm ² is reached, a signal for stopping screw reverse rotation is output to the input / output unit 32. At this time, the ring valve 9
If the closing is not surely performed and the molding conditions are disturbed, the value of P2 is changed by changing the value of k, and an appropriate coefficient k is obtained by retrying. Thereafter, P1 × k is automatically calculated for each molding cycle, and the reverse rotation of the screw 2 is stopped in a desired state.

As a result of various tests, the present inventor has found that when the ring valve is closed when the screw 2 is rotated in reverse, the pressure P
Has risen quite rapidly. When the rotation of the screw 2 is stopped when P reaches P × k = P2 during the ascent, the ring valve 9 is stopped.
It was also found that the molding was reliably closed and that there was no disturbance in the molding conditions. In the general molding, P2 at that time was approximately 20 to 30% of the oil motor pressure P1 during measurement.

[0025]

According to the present invention, since the ring valve can be securely closed before injection, the variation in the injection amount due to the backflow of the molten resin at the time of injection can be suppressed. Also, even if the nozzle is released after the filling of the gap is completed, the drawing from the nozzle is eliminated.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an injection molding machine according to the present invention.

FIG. 2 is a main block diagram of a control device.

FIG. 3 is a flowchart relating to main control.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating cylinder 2 ... Screw 3 ... Nozzle 4 ... Cylinder head 5 ... Screw head 6 ... Void 7 ... Through-hole 8 ... Screw body 9 ... Ring valve 10 ... Flow path 11 ... Notch 20 ... Oil motor 21 ... Electromagnetic direction switching Valve 22 ... Electromagnetic relief 23 ... Pressure sensor 25 ... Screw position detector 30 ... Control device 31 ... CPU 32 ... Input / output unit 33 ... Memory 34 ... Operation unit S1, S2 ... Solenoid

Claims

(57) [Reference number] C258 [Claims]

1. A ring which is inserted into a heating cylinder so as to be able to move forward and backward and to be rotatable, and which is in sliding contact with the inner wall of the heating cylinder and which is loosely fitted in a small diameter portion between the screw head and the screw body. A valve is disposed, a screw position detector for confirming the metering completion position, and the screw is rotated in a direction in which the molten material retreats based on a confirmation signal from the position detector, and the torque of the rotating screw is reduced. An injection molding machine comprising a control device for stopping rotation when a predetermined set value is reached.