JPH0458370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for monitoring abnormal pressure during rotation of a screw applied to an injection molding machine.

(Prior art) As a preparatory step for starting the injection molding machine's molding operation,
There is a step in which the molten resin is air shot and the resin temperature, resin weight, resin kneading state, etc. are monitored. At this time, in manual operation, the screw rotation (plasticization) → air shot → screw rotation → air shot is repeated, but when the screw is rotated for the first time, the resin in the screw cylinder is not completely melted. Rotation can lead to breakage of the screw head, screw body, etc., so to prevent this, a cold start prevention circuit has conventionally been provided. FIG. 3 shows a block diagram of a conventional cold start prevention circuit.

This circuit includes a band heater 4 for raising the temperature of the screw cylinder 3, a temperature sensor 5 for detecting the internal temperature of the screw cylinder, and a temperature setting device 6 for setting the temperature of the band heater 4. When the preset temperature is reached by the temperature setting device 6, a signal to that effect is sent to the molding machine control device 7, and the timer set by the time setting device 8 starts the clock, and when the timer times out, The signal is sent to the molding machine control device 7, and the screw rotation cold start prevention circuit is released for the first time here, allowing the screw to rotate. When the screw rotation switch (not shown) is turned on, high pressure oil is released from the hydraulic source. It is sent to the torque motor 1 and rotates the screw 2, thereby executing screw rotation (plasticization).

By the way, in the conventional cold start prevention circuit, if the setting time of the time setting device 8 is short, the screw 2 will rotate while the resin in the screw cylinder 3 remains unmelted, leading to the breakage accident mentioned above. I was afraid. Conversely, if the setting time of the time setter 8 is made longer, the start-up time of the molding operation becomes longer, resulting in a problem of lower productivity.

Furthermore, after startup, even during normal molding operation, iron scraps and resin materials are deposited from the hopper 9 into the cylinder 3.
If a foreign object such as a screw gets mixed in, the same foreign object may enter the screw 2.
There was also a problem in which the screw got stuck between the screw 2 and cylinder 3, damaging the screw 2, cylinder 3, etc.

(Problems to be Solved by the Invention) As described above, in the conventional cold start prevention circuit, if the setting time of the time setting device 8 is short, the screw may rotate while the resin in the screw cylinder remains unmelted. This may lead to an accident where the screw head, screw body, etc. break. In addition, if the time is long, the start-up time of the molding operation will be longer, resulting in a problem of lower productivity. Furthermore, when foreign matter enters the hopper during normal operation and gets caught between the screw cylinders, the circuit does not play any role and prevents damage to the screws, screw cylinders, etc. It was something that could not be prevented.

The present invention was made to solve these problems, and is capable of monitoring abnormal pressure during screw rotation, making it possible to prevent breakage accidents of screws, screw cylinders, etc., and to improve productivity in injection molding. It is intended to provide a method.

(Means for Solving the Problems) Therefore, the present invention provides a method for monitoring abnormal pressure during screw rotation in an injection molding machine, which detects the pressure at the inlet of a high torque motor and sets a preset monitoring pressure. In comparison, the system automatically performs the function of stopping the screw rotation when the pressure exceeds the monitoring pressure, and this is a means of solving the above-mentioned problems.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram for implementing the method of the invention. Incidentally, each member indicated by reference numerals 1 to 7 and 9 in the figure has the same function as that in FIG. 3, so a detailed explanation thereof will be omitted here.

In this embodiment, in addition to these members, a pressure sensor 10 for detecting the pressure at the "inlet" of the high torque motor is installed at the corresponding location, and a signal from this pressure sensor 10 and a monitoring value setting device 12 are connected. A comparator is provided to compare the signal with a preset set value signal. The comparison result by this comparator 11 is sent to the molding machine control device.

To explain the case of cold starting using such a control device, when the temperature of the screw cylinder 3 set by the temperature setting device 6 rises,
The signal is sent to the molding machine control device 7, where the screw rotation becomes possible (until this signal comes,
Even if the screw rotation switch is turned on, the screw 2 will not rotate.)

Next, in manual operation, when a screw rotation switch (not shown) is turned on, high pressure oil is sent from the hydraulic source to the high torque motor 1, and the screw 2 is rotated. At this time, the load on the screw 2 will change depending on whether the resin in the screw cylinder 3 is completely melted or not, and the "inlet" pressure of the high torque motor 1 will also change. .

Therefore, the monitoring pressure P is set by the monitoring value setting device 12, and the pressure detected by the pressure sensor 10 provided at the "inlet" of the high torque motor 1 is compared by the comparator 11, and the monitoring pressure is If it is lower than P, the screw continues to rotate, and if it is higher than P, a monitoring pressure over signal is sent from the comparator 11 to the molding machine control device 7 at point P shown in FIG. 2, and the hydraulic pressure is automatically turned off. A circuit is constructed to immediately stop the rotation of the screw and take measures to issue an alarm, such as turning on a warning light (not shown) or sounding a buzzer.

The above has explained the control mode at the preparatory stage for injection molding, but the control described above is not limited to control at this stage, but also during normal molding operation and when abnormal pressure occurs in the cylinder 3. is to be executed.

For example, during normal molding operation, the hopper 9
If foreign objects such as iron scraps and screws get into the cylinder 3 together with the resin raw material, the screw 2 and cylinder 3
These foreign objects get caught in between, increasing the load on the screw 2. As a result, when the "inlet" pressure of the high torque motor 1 exceeds the monitoring pressure P, a monitoring over signal is sent from the comparator 11 to the molding machine control device 7, as in the case of the cold start described above, and the It turns off the hydraulic power source, stops the screw rotation, and issues an alarm such as turning on a warning light (not shown) or sounding a buzzer.

(Effects of the Invention) As described above in detail, according to the present invention, it is possible to completely prevent the cold start of screw rotation, and main parts such as the screw and cylinder are prevented from being broken or damaged. There is no need to time up the time setting device, the screw rotates smoothly, the work to set various molding conditions can be started quickly, and the molding start-up time can be shortened.

Furthermore, according to the present invention, it is possible to detect abnormal pressure in the cylinder and take measures such as stopping the molding machine not only when the screw rotation is cold started but also during normal molding operation. It is.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an abnormal pressure monitoring circuit during screw rotation showing an embodiment of the present invention, Fig. 2 is a relationship diagram between high torque motor inlet pressure and screw rotation time in the present invention, and Fig. 3 is a conventional circuit. FIG. 2 is a block diagram of a cold start prevention circuit in an injection molding machine. Explanation of the main parts of the diagram, 1...High torque motor, 1
0...Pressure sensor, 11...Comparator, 12...Monitoring value setter.

Claims (1)

[Claims] 1 In a method of monitoring abnormal pressure during screw rotation of an injection molding machine, the pressure at the inlet of a high torque motor is detected, compared with a preset monitoring pressure, and if the pressure exceeds the monitoring pressure, A method for monitoring abnormal pressure during screw rotation in an injection molding machine, characterized by automatically performing each function of stopping the screw rotation.