JPH0445331B2 - - 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 are susceptible to thermal decomposition when overheated while staying in the cylinder. This is easy to happen, and in open nozzle injection molding machines, 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 If the hopper stops, 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, causing 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 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 results of the detection device. The purpose is to provide a decomposition prevention device.

[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 stops forward and backward movement and rotation in a screw in-line injection molding machine consisting of an injection device and a mold clamping device, and is brought into a neutral state. a screw position detector that detects the screw position in the controller and inputs it to the controller; a register that stores the screw position input to the controller; and an adder that adds a preset screw retraction allowance to the screw position memory value. and a comparator that compares the value added by the adder with the current screw position value that is subsequently inputted, and as the screw retreats due to the volumetric expansion of the molten resin, the current screw position value is equal to the value added by the adder. When the value exceeds the value, the controller will issue a resin thermal decomposition detection signal, and based on the resin thermal decomposition detection signal, the controller will issue an injection device retraction command, a shut-off mechanism open command, a hotspa shutter close command, a screw advance, and a screw A rotation command is sent, and the actuator moves the injection device forward and backward in accordance with the command, which causes the injection device to retreat, open the shutter-off valve provided on the injection nozzle, close the hopper shutter provided at the bottom of the hopper, and advance the screw. It was configured so that each operation of screw rotation was performed.

[Effect]

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, the start of thermal decomposition of the resin can be accurately grasped, and the molten resin can be Since the 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〕

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 front and rear servo motors 3 and a feedback circuit from the shutoff valve 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 rotated by the screw rotation motor 7a by driving the screw rotation solenoid 20 in accordance with the screw rotation command from the controller 4, and is moved forward and backward by the injection cylinder 7b. A screw position detector 7d is provided which engages with a rack 7c which is integrally constructed with the screw 7.

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 for adding a preset screw retraction allowance to the screw position memory value. 4b and the adder 4
A comparator 4c is provided for comparing the added value obtained by b and 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 shut-off 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 _x1 . The screw position x ₁
is reset when the screw operation is performed again, and the screw position which has become a new neutral state is stored.

Next, the adder 4b adds the preset retraction allowable amount Δx of the screw 7 to the screw _position When it is pushed back by pressure and the screw position reaches x ₂ , the comparator 4c detects x ₂ and x ₁ + Δx.
If x ₂ >x 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. 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 by the screw advance command, the screw forward and backward movement valve 7e is activated. operates to drive the injection cylinder 7b, and the screw 7
moves forward at a low speed and then rotates the screw to discharge the molten resin remaining in the heating cylinder 2d from the injection nozzle 1.

In the case of an open nozzle injection molding machine that does not have the shut-off valve 1a, the controller 4 issues commands for the remaining configuration positions from the above description except for the fully open position command of the shut-off valve based on the pyrolysis detection signal in the same manner as described above. put out.

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 a resin material sealed in a heating cylinder is detected early based on the amount of screw retraction due to volumetric expansion of the resin,
Since the molten resin is automatically discharged from the injection nozzle, it is possible to prevent the resin from spewing out from the hopper or injection nozzle, which has the effect of greatly improving the safety of the injection molding machine. It will be done.

[Brief explanation of drawings]

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 pyrolysis detection block diagram. DESCRIPTION OF SYMBOLS 1... Injection nozzle, 1a... Shutoff valve, 2... Injection device, 2a... Actuator (injection device forward and backward movement cylinder), 4... Controller, 4a... Register, 4b... Adder, 4c...
... Comparator, 7... Screw, 7d... Screw position detector, 8... Hopper, 8b... Hopper shutter.

Claims (1)

[Claims] 1 Screw position detection in a screw in-line injection molding machine consisting of an injection device and a mold clamping device, in which the screw position in a neutral state is detected by stopping forward and backward movement and rotation and is input to the controller 4. a register 4a for storing the screw position input to the controller 4, an adder 4b for adding a preset screw retraction allowance to the screw position storage value, and a register 4a for storing the screw position inputted to the controller 4; A comparator 4c is provided to compare the input current screw position value.
The controller 4 is configured to transmit a resin thermal decomposition detection signal when the screw 7 retreats due to the volumetric expansion of the molten resin and the current screw position value becomes larger than the added value by the adder 4b. Resin pyrolysis detection device for injection molding machines. 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
2. The resin according to claim 1, wherein the following operations are performed: opening a shutter off valve 1a provided at the bottom of the hopper 8, closing a hopper shutter 8b provided at the bottom of the hopper 8, advancing the screw 7, and rotating the screw. Pyrolysis prevention device.