JPH02171226A - Preventive device of resin pyrolysis of injection molding machine - Google Patents

Abstract

PURPOSE:To enable prevention of spouting of resin through a hopper or an injection nozzle, by a method wherein cubical expansion of molten resin closed up tightly within a heating cylinder is detected through an amount of backward movement of a screw. CONSTITUTION:At a point of time when a command of a forward or backward movement of a screw 7 or turning of the screw through a controller 4 is completed and the screw 7 becomes a neutral state, a signal of a screw position is applied to the controller 4 through a screw position detector 7d and a register 4a stores a screw position x1. Then an allowable amount DELTAx of a backward movement of the screw 7 established beforehand is added to the screw position x1 with an adder 4b, the screw 7 is moved backward by being pressed with expansion pressure of molten resin due to pyrolysis of the resin while the neutral state of the screw 7 is being continued. When a screw position comes to an x2, a comparator 4c makes a pylorysis detected signal by deciding that the resin on the inside of a heating cylinder 2d begins the pylorysis when (x2>x1+DELTAx) is given by comparing the x2 and (x1+DELTAx) with each other.

Description

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

[Prior Art] 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 are
Overheating while staying in the cylinder tends to cause thermal decomposition. For example, in an oven nozzle injection molding machine, the tip of the injection nozzle is pressed against the mold during the pressure holding and cooling process, and the mold is filled with resin. Therefore, if the molding machine stops due to some abnormality, not only will gas be generated from the resin stagnant in the heating cylinder, but the internal pressure of the heating cylinder will rise abnormally, causing resin material to eject from the hopper, which is dangerous for workers. condition may occur.

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 squirts out from the hopper or the shut-off mechanism is opened inadvertently. There is a particularly high risk of molten resin suddenly spewing out from the injection nozzle.

Therefore, a timer is installed in the controller, and if the injection nozzle is an open nozzle, the injection nozzle contacts 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 the injection nozzle is closed and a certain period of time has elapsed. The timer operates to automatically retract the injection device from the mold, and if a shutoff mechanism is provided, the shutoff mechanism is released for a time to discharge the molten resin in the heating cylinder from the injection nozzle.

[Problem to be solved by the invention] However, the time required for the resin to undergo thermal decomposition varies depending on the type of resin material and molding conditions, especially the set temperature of the heating cylinder, so it is difficult to accurately set the timer set time. Additionally, there is a problem in that if the injection nozzle is separated from the mold and the injection nozzle is opened or the shut-off mechanism is opened, a portion of the thermally decomposed resin remains in the heating cylinder without being discharged.

The present invention focuses on the above conventional problems, and provides a detection device that can accurately detect the start of resin thermal decomposition in a heating cylinder, and a resin heat detection device that can appropriately control an injection device based on the detection result of the detection device. The purpose is to provide a decomposition prevention device.

[Means for Solving the Problems] In order to achieve the above object, a resin thermal decomposition prevention device for an injection molding machine according to the present invention is provided in a screw in-line injection molding machine consisting of an injection device and a mold clamping device. A screw position detector detects the position of the screw in a neutral state after stopping advance and rotation and inputs it to the controller; a register that stores the screw position input to the controller; An adder that adds to the position memory value and a comparator that compares the added value by the adder with the current screw position value that is subsequently input are provided, and as the screw retreats due to the volumetric expansion of the molten resin, the screw position When the current value becomes larger than the value added by the adder, the controller transmits a resin thermal decomposition detection signal, and based on the resin thermal decomposition detection signal, the controller commands the injection device to retreat and the shut-off mechanism to open. , transmits a hopper shutter closing command, screw advance and screw rotation commands, and moves the injection device back and forth by actuating an actuator that moves the injection device forward and backward according to the command, opening a shunt-off valve provided at the injection nozzle, and opening a shunt-off valve provided at the bottom of the hopper. The hopper shutter was closed, the screw was moved forward, and the screw rotated.

[Function] According to the above configuration, since the volume expansion of the molten resin sealed in the heating cylinder is detected by the amount of retraction of the screw, it is possible to accurately grasp the start of thermal decomposition of the resin. Since the molten resin is automatically discharged from the injection nozzle, it is possible to prevent the resin from being ejected from the hopper or the injection nozzle.

[Example] Hereinafter, an example of the resin thermal decomposition prevention device for an injection molding machine according to the present invention will be described in detail with reference to the drawings.

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

The injection device 2 moves forward and backward by the hydraulic pressure applied from the hydraulic pump 6 to the injection device forward and backward movement cylinder 2a via the injection device forward and backward movement valve 6a, but there is an injection device front end limit switch near the forward and backward stroke end of the injection device 2. 2b and the injection device rear end limit switch 2C are respectively attached,
A signal is input to the controller 4.

Further, the screw 7 is rotated by the screw rotation motor 7a by driving the screw rotation solenoid 20 in response to a screw rotation command from the controller 4, and is moved forward and backward by the injection cylinder 7b. A screw position detector 7d that meshes with a rack 7C that is integrally constructed with the screw 7 is provided.

As shown in FIG. 2, the controller 4 includes a register 4a for storing the screw position input by the screw position detector 7d, and an adder 4b for adding a preset screw retraction allowance to the screw position memorized value. , and a comparator 4C for comparing the value added by the adder 4b with the current screw position value that is subsequently input. 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 starts to thermally decompose with the shutoff valve 1a closed, the volume of the resin expands and pushes the tip of the screw 7 in the backward direction, so the screw 7 moves backward. do.

When the screw forward/backward movement or screw rotation command from the controller 4 is completed and the screw 7 is in the neutral state, a screw position signal is input from the screw position detector 7d to the controller 4 as shown in FIG. 2, and the screw position signal is input to the register. 4a stores the screw position X+.

The screw position x1 is reset when the screw is operated again, and the new screw position in the neutral state is stored.

Next, the adder 4b adds the preset retraction allowable amount ΔX of the screw 7 to the screw position x1, and while the screw 7 remains in the neutral state, the expansion pressure of the molten resin When the screw is pushed back and the screw position reaches x2, the comparator 4
C compares x2 and x1+ΔX and finds that X 2 > X
If it becomes 1+ΔX, 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. Retract until it turns ON. Next, from the controller 4 to the servo amplifier 5
The servo motor 3 fully opens the shutoff valve la. Furthermore, the push-pull solenoid 8a is actuated by the hopper shutter closing command from the controller 4, the hopper shutter 8b is closed, and the supply of resin material from the hopper 8 into the heating cylinder 2d is cut off. 7e operates to drive the injection cylinder 7b, the screw 7 moves forward at a low speed and then rotates to discharge the molten resin remaining in the heating cylinder 2d from the injection nozzle 1.

In the case of an oven nozzle injection molding machine that does not have the shutoff valve 1a, the controller 4 issues commands to the remaining component devices in the same manner as described above, except for the shutoff valve fully open position command, based on the pyrolysis detection signal. put out.

In this example, a push-pull solenoid was 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. The shutoff mechanism of the injection nozzle is not limited to a limit switch, and may be a rotary variable valve or a needle valve, etc., and a hydraulic or mechanical link mechanism may be used in addition to a servo motor as a means for opening and closing the shutoff valve. The present invention can also be applied to.

[Effects of the Invention] As explained above, according to the present invention, the thermal decomposition of the resin material sealed in the heating cylinder is detected early by the amount of screw retraction caused by the volumetric expansion of the resin, and the molten resin is ejected from the injection nozzle. Since the resin is automatically discharged, it is possible to prevent the 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 the drawing]

FIG. 1 is a cross-sectional explanatory view of an injection device having an injection nozzle equipped with a shut-off valve according to an embodiment, and FIG. 2 is a block diagram for detecting thermal decomposition. l... Injection nozzle la... Shutoff valve 2... Injection device 2a... Actuator (injection device forward/backward cylinder) 4... Controller 4a... Register 4b... Adder 4c... Comparator 7... Screw 7d... Screw position detector 8... ...
Hopper 8b...Hopper shutter patent applicant Komatsu Ltd. Figure 2

Claims (2)

[Claims] (1) In a screw in-line injection molding machine consisting of an injection device and a mold clamping device, a screw position detector 7d detects the position of the screw in a neutral state after stopping forward and backward movement and rotation and inputs the detected position to the controller 4; A register 4a that stores the screw position input to the controller 4, an adder 4b that adds a preset screw retraction allowance to the screw position storage value, and the adder 4.
A comparator 4c is provided to compare the added value obtained by b and the current screw position value that is subsequently inputted, and as the screw 7 retreats due to the volume expansion of the molten resin, the current screw position value becomes the added value obtained by the adder 4b. 1. A resin pyrolysis detection device for an injection molding machine, characterized in that a controller 4 transmits a resin pyrolysis detection signal when the resin pyrolysis becomes larger. (2) Based on the resin thermal decomposition detection signal, the controller 4
transmits an injection device retraction command, a shut-off mechanism opening command, a hopper shutter closing command, a screw advance command, and a screw rotation command, and in response to the commands, the injection device 2 is moved back and forth by actuating the actuator 2a, and injection is performed. Claim 1, characterized in that the following operations are performed: opening a shut-off valve 1a provided at the nozzle 1, closing a hopper shutter 8b provided at the bottom of the hopper 8, advancing the screw 7, and rotating the screw. 1) The resin thermal decomposition prevention device described above.