JPH04284221A - Injection molding machine - Google Patents

Abstract

PURPOSE:To eliminate the resin backflow from a ring valve at the time of injection and lessen the unevenness of injection volume by improving the closing of the ring valve. CONSTITUTION:An injection molding machine is provided with a screw 2 fitted movably back and forth and rotatably through in a heating cylinder 1, and a ring valve 9 being slidably in contact with the inner wall of the heating cylinder and fitted movably in a small diameter section between a screw head 5 and a screw main body 8 is disposed on the screw 2. The injection molding machine is also provided with a screw position sensor 25 for confirming the metering completion position and a control device 30 for rotating the screw 2 in the direction in which a molten raw material is moved backward based on a confirming signal of said position sensor and stopping the rotation when the torque of the rotating screw reaches the given set value. The ring valve 9 is moved backward relatively to the screw 2, and the ring valve is blocked before the molten resin is injected into the mold by said arrangement.

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

[Prior Art] Injection molding machine screws are equipped with a backflow prevention ring between the screw body and the screw head in order to prevent the molten resin extruded to the nozzle side from moving to the screw body side during the operation of the injection process. has been done. When the molten resin is transferred forward into the screw groove by the rotation of the screw, this ring is pushed by the molten resin and moves toward the screw head and comes into contact with the rear end surface of the head. Therefore, the molten resin passes from the screw groove through the through hole of the backflow prevention ring, passes through the notch at the end of the screw head, and is accumulated in the gap in front of the screw head. When the metering process is completed, the screw moves forward to inject the accumulated molten resin, and the ring is in a relatively retracted position, moving from the screw head side toward the screw body, and the compressed molten resin acts on the screw body. Pushed by the molten resin flowing back to the side, the retreating surface of the ring comes into contact with the end surface of the screw body, closing the inner flow path of the ring.

However, the closing operation speed of this backflow prevention ring varies depending on the properties of the accumulated molten resin, and due to fluctuations in the operation speed, it is not possible to equalize the amount of filling resin injected into the mold.

For this reason, according to Japanese Patent Publication No. 59-47979, the screw head is provided with a lead screw in the same direction as the screw head body, and the screw is connected to the screw for a short time during the metering process after the metering process is completed or just before the start of the injection process. Discloses a method to ensure that the metered resin in front of the screw is filled into the mold without backflow at the start of the injection process by rotating the screw in the opposite direction to the rotation direction of the screw and closing the backflow prevention ring in advance due to the backflow of resin. has been done.

However, in this case, since the screw head is provided with a lead screw in the same way as the screw body, a head with a new size and shape must be custom-made.

Furthermore, there is a conventional method in which the gap in front of the screw is filled with molten resin and then sucked back. In this case, since the resin on the rear side of the ring valve is sent forward due to the suckback, there is a drawback that the resin is filled in an amount larger than the amount of resin at the time when the filling of the resin into the gap is completed.

[0007]

[Problems to be Solved by the Invention] In view of the above circumstances, an object of the present invention is to improve the closing of the ring valve, eliminate the backflow of resin from the ring valve during injection, and reduce variations in the injection amount. The purpose of the present invention is to provide an injection molding machine.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the injection molding machine of the present invention is provided with a screw that is fitted into a heating cylinder so that it can move forward and backward and rotatably, and the screw is attached to an inner wall of the heating cylinder. A ring valve is placed in sliding contact and loosely fitted in the small diameter part between the screw head and the screw body,
A screw position detector to check the measurement completion position,
A control device is provided for rotating the screw in a direction in which the molten raw material retreats based on a confirmation signal from the position detector, and for stopping the rotation when the torque of the rotating screw reaches a predetermined set value. It is characterized by

[0009]

[Function] According to this configuration, after the measuring process is completed by the screw rotation, when the screw rotates in the opposite direction to the measuring process,
Since the molten resin on the rear side of the ring valve is sent to the rear,
Since a pressure difference occurs between the front side and the rear side of the ring valve, the ring valve moves back toward the screw body and closes the valve.

The reverse rotation of the screw is stopped when the torque of the screw reaches a predetermined set value, that is, when the ring valve has completely closed and the molding conditions are not disturbed in any way.

[0011]

[Embodiment] An embodiment of the present invention will be explained based on 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, which is used to plasticize resin falling from a hopper (not shown) using a screw 2. A cylinder head 4 is attached to the tip of the heating cylinder 1 and includes a nozzle 3 that comes into contact with a sprue bush of a mold. A conical gap 6 is provided at the rear of the nozzle to match the shape of the tip of the screw head 5, and communicates with a through hole 7 through which the screw 2 moves forward and backward within the heating cylinder 1.

The screw 2 consists of a screw body 8 equipped with a lead screw 2a for transferring the resin falling from the hopper to the nozzle 3 side while melting and kneading it, and a screw head 5 connected to the tip of the screw body 8. 8 and the head 5 is a small diameter part, and a ring valve 9 for preventing backflow of molten resin is movably fitted between the rear end surface B of the screw head 5 and the front end surface 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, and is further provided with a notch 11 at the tip end of the ring valve 9 or on the side of the screw head 5, and a notch 11 is provided at the small diameter rear end 5a of the screw head 5. A flow path 10 for molten resin, indicated by an arrow P, is formed between the screw head 5 and the screw head 5 so that the molten resin flows into the gap 6 on the front side of the screw head.

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 directional control valve that can supply hydraulic oil so that the oil motor 20 rotates in the forward direction when the solenoid S1 is energized, and rotates in the reverse direction when the solenoid S2 is energized. 22 is an electromagnetic relief valve that adjusts the pressure of hydraulic oil supplied to the oil motor 20. A pressure sensor 23 outputs an electric signal corresponding to the pressure of hydraulic oil supplied to the oil motor 20. Note that 25 is a screw position detector.

30 is the main control device of the injection molding machine;
1 is a CPU of the control device 30, 32 is an input/output section, 33 is a memory, and 34 is an operation section.

The main points of the operation of the injection molding machine having such a configuration will be explained based on the flowchart shown in FIG.

Prior to injection, a metering process is started to store a predetermined amount of molten raw material in the cavity 6. That is, the CP that has received the weighing process start signal from the input/output unit 32
U31 transmits the Kudo maximum hydraulic pressure of the oil motor 20, which has been previously set and stored in the memory 33 by the operator, to the input/output section 32. The input/output section 32 receives the maximum driving hydraulic pressure, for example, 175 kg.
/cm2 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 source passes through the electromagnetic directional control valve 21 to the oil motor 2 while its maximum pressure is regulated to, for example, 175 kg/cm2.
0, the oil motor 20 and the screw 2
rotates forward. Raw materials supplied from a hopper (not shown) are transferred forward through the heating cylinder 1 while being plasticized by the rotation of the screw 2 . The screw 2 retreats by the amount that the plasticized raw material is transferred to the gap 6, and when it reaches the preset metering completion position, the input/output unit 32 detects the metering completion position based on the detection signal from the screw position detector 25. issue a command. Solenoid S1 and electromagnetic relief 22 of electromagnetic directional control valve 21 are demagnetized, and rotation of oil motor 20 is stopped.

During this metering process, the pressure P1 actually supplied to the oil motor 20 is detected by the pressure sensor 23 and stored in the memory 33 of the main controller 30. That is, in this embodiment, the torque of the screw 2 is easily determined in the form of the actual measured value of the oil pressure supplied to the oil motor 20 without requiring a complicated mechanism.

[0021] When the measuring process is completed, the CPU 31 instantly reads the pressure P stored in the memory 33.
The product P2 of 1 and k is calculated. k here is a numerical value of 1 or less, usually about 0.2 to 0.3.

Assume now that k is set to 0.3 and stored in the memory 33. And the above P1 is 100kg/c
If it is m2, then P2=P1×k=100×0.3=30kg/cm2.

When the metering process is completed and P2 is calculated, the solenoid S2 of the electromagnetic directional control valve 21 is energized to ensure that the ring valve 9 is closed prior to the injection process, and the screw 2 is rotated in the reverse direction. will be held. The supplied oil pressure P of the oil motor 20 detected by the pressure sensor 23 is taken into the CPU 31 of the main control device 30, and the magnitude of P and the above-mentioned P2 is continuously compared and calculated. Then, when P reaches P2, here 30 kg/cm2, a signal to stop the reverse rotation of the screw is output to the input/output section 32. At this time, if the ring valve 9 is not closed reliably and the molding conditions are disturbed, change the value of P2 by changing the value of k, and try again to find an appropriate coefficient k. Ask for it. 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 inventor found that when the ring valve is closed when the screw 2 is reversed, the pressure P
We found a phenomenon in which there was a fairly rapid rise in Then, when P reaches P x k = P2 during the rise, if the screw 2 is stopped from reversing, the ring valve 9 will be reliably closed and the molding conditions will not be disturbed at all. We found that together. In general molding, P2 at that time was approximately 20 to 30% of the oil motor pressure P1 during metering.

[0025]

According to the present invention, since the ring valve can be reliably closed before injection, it is possible to suppress variations in the injection amount due to backflow of molten resin during injection. Further, even if the nozzle is released after filling the gap, there is no drawling from the nozzle.

[Brief explanation of the drawing]

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

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

FIG. 3 is a flowchart related to main control.

[Explanation 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...Solenoid directional valve 22...Electromagnetic relief 23...Pressure sensor 25...Screw position detector 30...control device 31...CPU 32...Input/output section 33...Memory 34...Operation unit S1, S2...Solenoid

Claims (1)

[Claims] 1. A screw is provided in the heating cylinder so as to be movable forward and backward and rotatable, and a ring is fitted to the screw in sliding contact with the inner wall of the heating cylinder and loosely fitted in a small diameter portion between the screw head and the screw body. A screw position detector is provided to confirm the measurement completion position, and the screw is rotated in a direction in which the molten raw material retreats based on a confirmation signal from the position detector, and the torque of the rotating screw is An injection molding machine characterized by comprising a control device for stopping rotation when a predetermined set value is reached.