JPH057173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and a device for preventing seizure of a screw during idle rotation in an injection molding machine. The present invention relates to a method and device for preventing screw seizure in an injection molding machine.

(Prior art) An in-line screw type injection molding machine transports the molded resin material supplied into the barrel forward while plasticizing and kneading it by the rotation of the screw, and places it in the measuring section at the front end of the barrel. When a certain amount of molten resin has accumulated, the molten resin is forced into the cavity of the mold by moving the screw forward. In such an injection molding machine, during the plasticizing process of plasticizing and kneading the resin material, the screw is moved back by the back pressure of the molten resin that accumulates in front of the screw. Therefore, normally the screw is not rotated at a fixed position for a long period of time.

However, when the screw is rotated by mistake without material being supplied, or when the screw is in a surging state where the material is not inserted into the screw even though it is rotating, the front of the screw may Since back pressure does not increase, the screw rotates at a constant position.
If the screw continues to rotate at a fixed position, that is, if the screw continues to idle for a long time, the flight portion on the outer periphery of the screw will become stuck to the inner surface of the barrel.
In order to prevent such burn-in, it is necessary to be able to detect when the screw spins idly.

Conventionally, in order to detect such idling of the screw, the time required for plasticizing and measuring the material is set in a timer, and when the measuring is not completed within that time, that is, the screw does not retreat to a predetermined position. At that time, there was something that caused an alarm signal to be generated. The main purpose of this was to detect material shortages or material shortages during molding, but even if the screw spun, the measurement would not be completed within the set time. Idle rotation of the screw can be detected.

(Problem to be Solved by the Invention) However, when attempting to detect the slippage of the screw using such a method, it is necessary to prevent an alarm signal from being generated when correct plasticization measurement is performed. In order to do this, the time set on the timer must be longer than the screw rotation time during normal operation. On the other hand, at the beginning of the plasticization process,
In other words, when the screw starts rotating, a load is suddenly applied to the screw and its rotational drive device.
During this period, the screw is likely to slip due to poor penetration of the material. And once the Skrill starts spinning, it generally doesn't stop spinning.

For this reason, in the method for detecting screw rotation as described above, the idle rotation of the screw is detected only after a long set time set in the timer has elapsed after the screw rotation occurs, and the idle rotation continues during that time. It is difficult to prevent screw burn-in.

The present invention has been developed in view of the above problems, and its purpose is to prevent the screw from spinning as much as possible, and to quickly detect when the screw does slip, thereby preventing the screw from spinning. The purpose is to ensure that burn-in is prevented.

(Means for Solving the Problem) In order to achieve this object, in the present invention, at the start of the plasticizing process in which the screw is rotationally driven, the rotation speed of the screw is made smaller than the rotation speed during steady operation. At the same time, during the subsequent plasticizing process, the retraction speed of the screw is detected, and when the detected value falls below the allowable value, it is assumed that the screw is idling and the rotational speed of the screw is reduced again. There is.

In that case, the rotating load of the screw is also detected,
It is desirable to reduce the number of revolutions of the screw even when the detected value is outside the permissible range.

(Function) As described above, at the start of the plasticizing process, that is, when the screw starts rotating, the screw suddenly starts rotating, causing poor penetration of the material, so the screw is likely to idle. Therefore, the screw rotation speed at that time is reduced.
This reduces the occurrence of such problems such as poor penetration of the material, and prevents the screw from spinning idly at the start of the plasticizing process.

Additionally, if the screw spins idly during the plasticizing process, the screw usually stops retreating. Therefore, by detecting the backward speed of the screw and comparing it with a permissible value, it is possible to immediately detect when the screw is idling. Further, when the screw is idle with no material being supplied, the rotational load on the screw is extremely small, and when it is idle with no conveyance due to clogging with foreign matter such as iron pieces, the rotational load on the screw becomes large. Therefore, idling of the screw can also be detected by detecting the rotational load on the screw. If both of them are used together, slippage of the screw can be detected more reliably.

In this manner, by detecting the retraction speed of the screw and further its rotational load, idle rotation of the screw during the plasticizing process can be immediately detected. By lowering the number of rotations of the screw when it is determined that the screw is idling, seizure of the screw can be prevented.

(Example) Hereinafter, an example of the present invention will be described using the drawings.

The figure shows an example of a device for carrying out the method for preventing burn-in of a screw according to the present invention. FIG. 1 is an overall configuration diagram of the device, and FIG. 2 is a block circuit of an alarm signal generating device, which is a main part thereof. It is a diagram.

As is clear from FIG. 1, a screw 1 of the in-line screw injection molding machine is fitted into a barrel 2. An injection nozzle 3 is attached to the front end (left side in the figure) of this barrel 2, and a material supply port 5 is provided on the upper surface of the rear end to guide the material supplied from the hopper 4 into the barrel 2. .
The screw 1 is driven forward by an injection cylinder 6 and rotated by a hydraulic motor 7.

The hydraulic motor 7 is driven by high-pressure hydraulic oil supplied from a hydraulic source 8 such as a hydraulic pump. A proportional flow control valve 10 and a process switching valve 11 are provided in an oil passage 9 that leads hydraulic oil from the hydraulic power source 8 to the hydraulic motor 7.
By adjusting the opening degree of 0, the rotation speed of the hydraulic motor 7 is controlled, and by switching the switching valve 11, the hydraulic motor 7 is rotated or stopped. Therefore, the flow control valve 10
The rotation speed of the screw 1 is controlled by the screw 1, and the rotation and stop of the screw 1 is controlled by the switching valve 11. That is, in this embodiment, the flow rate control valve 10 constitutes a screw rotation speed control device.

The flow control valve 10 is controlled by a process controller 12 that automatically adjusts the operating conditions of the injection molding machine. Further, the process switching valve 11 is switched and controlled by a sequence controller 13 that cooperates with the process controller 12 thereof. Furthermore, the injection cylinder 6 is also controlled by these controllers 12 and 13. Therefore,
The injection molding machine uses these controllers 12, 13
automatically driven by.

The hydraulic pressure applied to the hydraulic motor 7, that is, the rotational load pressure of the screw 1, is detected by a pressure sensor 14, which is a load detector. Further, the backward speed of the screw 1 is detected by a speed sensor 15, which is a speed detector such as a potentiometer. Output signals from these sensors 14 and 15 are led to an alarm signal generator 18 via amplifiers 16 and 17, respectively.

As shown in FIG. 2, this alarm signal generator 18 has a pressure upper limit and a lower limit, respectively, for the rotational load pressure of the screw 1 during normal operation, that is, the allowable upper and lower limits thereof are set. A setting device 19, a pressure lower limit setting device 20, a time setting device 21 for setting the time required for the screw 1 to reach a steady operating state after the rotation starts, and a speed setting device for setting the allowable backward speed value of the screw 1. 22
and is provided. And the pressure setting device 19,
20 is connected to the pressure comparator 23, and the pressure sensor 1
4 and the pressure setting device 19,
The detected value is compared with each tolerance value set in 20, and when the detected value is not within the tolerance value range, a signal is output. Further, the speed setter 22 is connected to a speed comparator 24 so that a signal is output when the detected value detected by the speed sensor 15 is smaller than an allowable value set in the speed setter 22. ing.

The output signals of the pressure comparator 23 and the speed comparator 24 are input to an OR circuit 25,
When a signal is output from at least one of 3 and 24, an alarm signal is output from the OR circuit 25. The alarm signal is
The process controller 1 via the control circuit 26
2 and the sequence controller 13, and after being amplified by the amplifier 27, it is also sent to the flow rate control valve 10. In that case, the alarm signal is controlled by mode signals from the process controller 12 and sequence controller 13 that are input to the control circuit 26.

Next, the operation of the screw seizing prevention device in the injection molding machine configured as described above will be explained.

When the injection molding machine is automatically operated, the process controller 12 and the sequence controller 13 control the flow control valve 10 and the process switching valve 11 to control the hydraulic motor 7 and the injection cylinder 6.

First, when the injection process and the pressure holding process in the previous molding cycle are completed, the plasticizing process in the next molding cycle is started. This plasticizing process leaves the injection cylinder 6 in a free state, and
This is done by switching the process switching valve 11 and supplying high pressure hydraulic oil from the hydraulic source 8 to the hydraulic motor 7.

When the hydraulic motor 7 operates, the screw 1 is driven to rotate, and the material introduced into the barrel 2 from the hopper 4 is conveyed to the front of the barrel 2 while being plasticized and kneaded by the rotation of the screw 1. The plasticized and molten material is then stored in the barrel metering section between the front end surface of the screw 1 and the injection nozzle 3. Then, back pressure is applied to the front end surface of the screw 1, and the screw 1 starts to move backward.

When the screw 1 starts rotating, the time setting device 21
starts operating, a signal is output from the control circuit 26, amplified through the amplifier 27, and then sent to the flow control valve 10. The opening degree of the flow rate control valve 10 is restricted by the output signal thereof. As a result, the hydraulic motor 7 rotates at a low speed until the time set in the time setting device 21 has elapsed. In this way, the rotational speed of the screw 1 at the start of rotation is made smaller than the predetermined rotational speed during steady operation,
At the start of rotation, a sudden load is prevented from being applied to the screw 1 and the hydraulic motor 7, which is its rotational drive device. This prevents the screw 1 from spinning idly at the start of the plasticizing process.

During this time, the process controller 12
and from the sequence controller 13 to the control circuit 2
The mode signal sent to controller 6 blocks the alarm signal sent to those controllers 12 and 13. Therefore, an increase in the load pressure when the screw 1 starts rotating will not be considered as idling of the screw 1.

When the time set in the time setting device 21 has elapsed, the screw 1 is driven to rotate at a constant rotation speed. The load pressure applied to the hydraulic motor 7 is detected by the pressure sensor 14, and the backward speed of the screw 1 is detected by the speed sensor 15. The values detected by the sensors 14 and 15 are set by the setting devices 19 and 20 of the alarm signal generator 18,
If the signal is within the range of each allowable value set in 22, no signal is output from any of the comparators 23 and 24. Therefore, the injection molding machine has a controller 1
2 and 13, and after completing a predetermined measurement, the screw 1 is driven forward by the injection cylinder 6, so that the molten resin stored in the measurement part is injected from the injection nozzle 3. . and,
The molding cycle is completed after the steps of holding pressure, cooling, and opening the mold.

In the plasticizing process in which the screw 1 is rotationally driven, when material is not being supplied from the hopper 4 into the barrel 2 or in a surging state, the driving load on the screw 1 is small, so the pressure sensor 1
The detected value detected by 4 is the pressure lower limit setter 2.
This will fall below the allowable lower limit set to 0.
Furthermore, if a foreign object such as a piece of iron enters the barrel 2 and becomes clogged, the driving load on the screw 1 increases, and the detected value of the pressure sensor 14 exceeds the allowable upper limit set in the pressure upper limit setting device 19. In either of these cases, the material is not conveyed to the weighing section in front of the barrel 2, so the screw 1 does not move back and the value detected by the speed sensor 15 falls below the allowable value set in the speed setting device 22. Become.

Therefore, when such idling of the screw 1 occurs, the pressure comparator 23 and the speed comparator 2
A signal is always output from at least one of 4.
As a result, OR circuit 25 generates an alarm signal. At this time, the alarm signal is sent to the process controller 12 and sequence controller 13. Sequence controller 13
receives the signal and shuts off the process switching valve 11. In this way, the hydraulic motor 7 is stopped and the rotation of the screw 1 is stopped.

Then, the alarm signal is transmitted to the controller 12,1.
3, the operation of the injection molding machine is stopped after completion of each process such as cooling and mold opening, that is, after completion of the current molding cycle.

In this way, when the rotational load or retraction speed of the screw 1 deviates from the allowable value, idle rotation of the screw 1 is detected, and the rotation of the screw 1 is promptly stopped. Therefore, seizure due to idle rotation of the screw 1 is prevented.

When the injection molding machine is being operated manually, no signals are emitted from the process controller 12 and the sequence controller 13. however,
Also at this time, when the screw 1 starts rotating, the screw 1 is driven to rotate at a low speed by a signal from the time setter 21. Furthermore, even when the screw 1 idles, a signal is output from at least one of the comparators 23 and 24, so the OR circuit 25
outputs an alarm signal. Then, the alarm signal is amplified by the amplifier 27 and sent to the flow control valve 10, so the flow control valve 10 is throttled.
The rotational speed of the hydraulic motor 7 decreases.

In this way, even during manual operation, when the screw 1 idles, the rotational speed of the screw 1 is reduced, and seizure of the screw 1 is prevented.

In the above embodiment, the idling of the screw 1 is controlled by the rotational load pressure of the hydraulic motor 7 and the screw 1.
However, slipping of the screw 1 can also be detected only by the fact that the backward speed of the screw 1 becomes smaller than the allowable value. Therefore, it is also possible to provide a seizure prevention device that determines whether the screw 1 is idling based only on the backward speed of the screw 1. However, the speed sensor 15, etc. that detects the backward speed of the screw 1 may fail, so in order to ensure that slipping detection is performed even in the event of a failure, it is necessary to use the method described in the above embodiment. It is desirable to detect slippage based on both the rotational load and the retraction speed.

Furthermore, the present invention is applicable not only to an injection molding machine in which the screw 1 is rotationally driven by the hydraulic motor 7 as in the above embodiment, but also to an injection molding machine in which the screw 1 is driven by an electric motor. be able to. In that case, the rotational load on the screw 1 may be detected based on the load current of the motor.

(Effects of the Invention) As is clear from the above description, according to the present invention, the number of revolutions of the screw is lowered at the start of the plasticizing process, thereby preventing the screw from idling due to poor penetration of the material, etc. This makes it possible to reduce the occurrence of idling. Furthermore, since the retraction speed of the screw is monitored during the plasticizing process, when the screw spins idly, the retraction speed decreases, and the slip is quickly detected. Furthermore, if the rotational load of the screw is also detected at that time, the slippage of the screw can be detected more reliably. In this way, when idle rotation of the screw is detected, the rotational speed of the screw is reduced to a predetermined low rotational speed or zero, that is, the rotation of the screw is stopped, thereby preventing the screw from seizing. Moreover, it is possible to reliably prevent this.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the screw burn-in prevention device according to the present invention, and FIG.
FIG. 2 is a block circuit diagram of an alarm signal generating device which is a main part thereof. DESCRIPTION OF SYMBOLS 1... Screw, 2... Barrel, 7... Hydraulic motor (screw rotation drive device), 10... Flow rate control valve (screw rotation speed control device), 11... Process switching valve, 12... Process controller, 13 …
... Sequence controller, 14 ... Pressure sensor (load detector), 15 ... Speed sensor (speed detector), 18 ... Alarm signal generator, 19 ...
Pressure upper limit setter (load setter), 20...Pressure lower limit setter (load setter), 21...Speed setter,
23, 24... Comparator.

Claims (1)

[Scope of Claims] 1. At the start of the plasticizing process in which the screw of the injection molding machine is rotated and retreated, the screw is rotationally driven at a lower speed than a predetermined rotation speed during steady operation, and the subsequent plasticization A screw screw in an injection molding machine, which continuously detects the backward speed of the screw during the process, and when the detected value becomes smaller than a preset tolerance value, reduces the rotational speed of the screw. How to prevent burn-in. 2. During the plasticizing process, the rotational load of the screw is continuously detected, and even when the detected value deviates from a preset tolerance value, the rotational speed of the screw is reduced. . A method for preventing screw seizure in an injection molding machine according to claim 1. 3. When the detected value deviates from the allowable value, the rotation of the screw is stopped, and the operation of the injection molding machine is stopped after cooling and mold opening steps are completed. 2. A method for preventing screw seizure in an injection molding machine according to 1 or 2. 4. In an injection molding machine equipped with a controller that automatically adjusts operating conditions; a load detector and a speed detector capable of respectively detecting the rotational load and retraction speed of the screw in the plasticizing process in which the screw retracts while being rotationally driven; , a load setting device and a speed setting device in which respective allowable values of the screw rotation load and retraction speed are set, and each of the allowable values set in these setting devices and each detection detected by each of the above-mentioned detectors. When at least one of the detected values deviates from the permissible value, an alarm signal is sent to the controller to stop the rotation of the screw and terminate the molding cycle at that time. and an alarm signal generating device for stopping the injection molding machine. 5. The screw seizure prevention device for an injection molding machine according to claim 4, wherein the screw rotation speed control device controlled by the controller is also controlled by the alarm signal.