JPH0445332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a resin thermal decomposition prevention device for an injection molding machine, and more particularly to a resin thermal decomposition prevention device for a screw-in-line injection molding machine.

[Conventional technology]

Conventionally, there are many types of resins used for molding in screw-in-line injection molding machines, but among them, crystalline resins such as nylon, polycarbonate, and vinyl chloride cause thermal decomposition when overheated while staying in the cylinder. In an open nozzle injection molding machine, for example, during the pressure holding and cooling process, the injection nozzle tip is pressed against the mold and the mold is filled with resin, so if some abnormality occurs, the molding machine may stop working. If the heating cylinder is stopped, not only will gas be generated from the resin accumulated in the heating cylinder, but the internal pressure of the heating cylinder will rise abnormally, resulting in a dangerous situation for the operator, such as resin material spewing out from the hopper. In addition, in injection molding machines equipped with a shut-off mechanism in the injection nozzle, the injection nozzle is closed except during the injection and pressure holding processes, so if the resin material is squirted from the hopper or the shut-off mechanism is opened inadvertently, the injection nozzle may There is a particularly high risk of molten resin suddenly spewing out. Therefore, a timer is provided in the controller, and if the injection nozzle is an open nozzle, the injection nozzle is in contact with the mold and a certain period of time has elapsed, and if the injection nozzle has a shut-off mechanism, the injection nozzle is closed and a certain period of time has elapsed. is activated to automatically retract the injection device from the mold, and
If a shut-off mechanism is provided, the shut-off mechanism is opened and the molten resin in the heating cylinder is discharged from the injection nozzle.

[Problem to be solved by the invention]

However, the time required for the resin to thermally decompose varies depending on the type of resin material and molding conditions, especially the set temperature of the heating cylinder, making it difficult to set the timer accurately and also removing the injection nozzle from the mold. There was a problem in that if the injection nozzle was separated or the shut-off mechanism was only opened, a part of the thermally decomposed resin would not be discharged and would remain in the heating cylinder.

The present invention focuses on the above-mentioned conventional problems, and provides a detection device that can accurately grasp the start of resin thermal decomposition within a heating cylinder, and an injection device that is appropriately controlled based on the detection result of the detection device. An object of the present invention is to provide an apparatus for preventing resin thermal decomposition by automatically discharging the resin remaining inside.

[Means to solve the problem]

In order to achieve the above object, the resin thermal decomposition prevention device for an injection molding machine according to the present invention suppresses the pressure of the actuator that moves the screw back and forth in a screw in-line injection molding machine consisting of an injection device and a mold clamping device. A pressure sensor that detects and inputs it to the controller is provided, and a comparator that compares the actuator pressure value input to the controller with the actuator pressure setting value input in advance, and when the actuator pressure value exceeds the actuator pressure setting value. In this case, the controller transmits a resin thermal decomposition detection signal, and based on the resin thermal decomposition detection signal, the controller transmits an injection device retreat command, a shutter-off mechanism open command, a hotspa shutter close command, and a screw advance command, and Retraction of the injection device by actuation of an actuator that moves the injection device back and forth,
Opening the shutter-off valve provided on the injection nozzle, closing the hopper shutter provided at the bottom of the hopper, advancing the screw by operating an actuator that moves the screw back and forth, and rotating the screw by operating the actuator that rotates the screw. configured to work.

[Effect]

According to the above configuration, the increase in the internal pressure of the heating cylinder is detected by the pressure of the actuator for moving the screw back and forth, so it is possible to accurately determine the start of thermal decomposition of the resin, and the molten resin is automatically transferred from the injection nozzle. Since the resin is discharged from the hopper or injection nozzle, it is possible to prevent resin from being ejected from the hopper or injection nozzle.

〔Example〕

Embodiments of the resin thermal decomposition prevention device for an injection molding machine according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional explanatory view of an injection device 2 having an injection nozzle 1 and a rotary shut-off valve 1a as a shut-off mechanism. The shut-off valve 1a is connected to a servo motor 3 via a rod 1b, and a shut-off valve position detector 3a is attached to the servo motor 3. A command circuit for the servo motor 3 and a feedback circuit from the shut-off position detector 3a to the servo amplifier 5 are provided.

The injection device 2 is connected to an injection device forward and backward movement cylinder 2a via a hydraulic pump 6 and an injection device forward and backward movement valve 6a.
An injection device front end limit switch 2b and an injection device rear end limit switch 2c are installed near the forward and backward stroke ends of the injection device 2, respectively, and input signals to the controller 4. ing.

Further, the screw 7 is connected to a screw rotation motor 7.
A, the injection cylinder 7b rotates, and the injection cylinder 7b moves back and forth. A pressure sensor 7c is provided in the head side piping of the injection cylinder 7b, and a feedback circuit that inputs the detection result to the controller 4 as a pressure signal connects the pressure sensor 7c and the controller. 4.

As shown in FIG. 2, the controller 4 includes an amplifier 4a that amplifies the injection cylinder pressure signal inputted by the pressure sensor 7c, and an injection cylinder pressure setting value and the injection cylinder pressure value inputted in advance. A comparator 4b for comparing the two is provided. Further, a hopper shutter 8b is attached to the bottom of the hopper 8 and is opened and closed by a push-pull solenoid 8a for opening and closing the hopper shutter.

When the resin accumulated in the front part of the heating cylinder 2d with the shut-off valve 1a closed starts to thermally decompose, the volume of the resin expands and pushes the tip of the screw 7 backward, and accordingly, the injection cylinder 7
Since the piston b is also pushed backward, the oil pressure on the injection cylinder head side increases. The pressure sensor 7
The comparator 4b compares the pressure _e1 on the injection cylinder head side detected by c and inputted to the controller 4 with the preset and input pressure set value _e2 when the screw is neutral, and the screw 7 moves forward or backward. and when the rotation is stopped and there is no operation, and e ₁ > e ₂
If so, it is determined that the resin in the heating cylinder 2d has started thermal decomposition, and a thermal decomposition detection signal is transmitted.

The controller 4 outputs an injection device retraction command based on the thermal decomposition detection signal, operates the injection device forward/backward movement valve 6a, operates the injection device forward/backward movement cylinder 2a, and moves the injection device 2 to the injection device rear end limit switch 2c. Reverse it until it turns on. Next, the controller 4 instructs the servo amplifier 5 to fully open the shutoff valve, and the servo motor 3 fully opens the shutoff valve 1a. Furthermore, the push-pull solenoid 8a is actuated by the hopper shutter closing command from the controller 4 to close the hopper shutter 8b, cutting off the supply of resin material from the hopper 8 into the heating cylinder 2d, and the screw forward movement valve 7d is activated by the screw advance command. The screw rotation valve 20 operates to drive the injection cylinder 7b, causing the screw 7 to move forward at a low speed, and then the screw rotation valve 20 operates to drive the screw rotation motor 7a to rotate the screw 7, removing the remaining melt in the heating cylinder 2d. The resin is discharged from the injection nozzle 1.

In the case of an open nozzle injection molding machine that does not have a shutoff valve 1a, the controller 4 issues the remaining commands except for the shutoff valve fully open position command based on the pyrolysis detection signal.

In this embodiment, a push-pull solenoid is used as the actuator for opening and closing the hopper shutter, but a hydraulic or pneumatic cylinder may also be used, or the hopper shutter may not be provided. Furthermore, detection of the forward/backward position of the injection device is not limited to a limit switch, and the shut-off mechanism of the injection nozzle may be a rotary variable valve or a needle valve, etc. The shut-off valve can be opened/closed using hydraulic or mechanical means in addition to a servo motor. The present invention can also be applied to those using a type link mechanism.

〔Effect of the invention〕

As explained above, according to the present invention, thermal decomposition of the resin material sealed inside the heating cylinder is detected early based on the amount of pressure rise on the injection cylinder head side, and the molten resin is automatically discharged from the injection nozzle. This makes it possible to prevent resin from being ejected from the hopper or the injection nozzle, resulting in the effect that the safety of the injection molding machine can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory diagram of an injection device equipped with a shut-off valve in an injection nozzle according to an embodiment, and FIG.
The figure is a block diagram of thermal decomposition detection within the controller. DESCRIPTION OF SYMBOLS 1... Injection nozzle, 1a... Shutoff valve, 2... Injection device, 2a... Actuator (injection device forward and backward movement cylinder), 4... Controller, 4b... Comparator, 7... Screw, 7a...
...actuator (screw rotation motor), 7
b... Actuator (injection cylinder), 7c...
...Pressure sensor, 8... hopper, 8b... hopper shutter.

Claims (1)

[Claims] 1. In a screw in-line injection molding machine comprising an injection device and a mold clamping device, the screw 7
a pressure sensor 7c that detects the pressure of the actuator 7b that moves back and forth and inputs it to the controller 4;
and a comparator 4b that compares the actuator pressure value input to the controller 4 with the actuator pressure set value input in advance, and when the actuator pressure value exceeds the actuator pressure set value, the controller 4 A resin pyrolysis detection device for an injection molding machine, characterized in that it transmits a pyrolysis detection signal. 2 Based on the resin thermal decomposition detection signal, the controller 4 issues an injection device retraction command, a shutter-off mechanism opening command, a hopper shutter closing command, a screw advance command, and a screw rotation command, and the actuator 2 moves the injection device 2 forward and backward according to the commands.
Retraction of injection device 2 due to operation of a, injection nozzle 1
Opening of the shutter off valve 1a provided at the bottom of the hopper 8, closing of the hopper shutter 8b provided at the bottom of the hopper 8, advancement of the screw 7 by actuation of the actuator 7b which moves the screw 7 back and forth, and actuation of the actuator 7a which rotates the screw 7. 2. The apparatus for preventing thermal decomposition of resin according to claim 1, wherein each of the following operations is performed: rotation of the screw 7.