JPH0425427A - Breakage of screw preventing device for injection molding machine - Google Patents

Abstract

PURPOSE:To surely prevent breakage of a screw by detecting the pressure difference of the suction side and the discharge side of an oil motor and obtaining the generating torque of this oil motor and stopping the oil motor when this obtained value reaches the set rate of torsion stress of the screw. CONSTITUTION:Pressure sensors 5, 6 are provided to the suction side and the discharge side of an oil motor 2 and the pressure of oil is detected. The difference of the detected value of the pressure sensors 5, 6, namely the pressure difference is memorized to a controller 7. The generating torque of the oil motor 2 is obtained from this pressure difference by conversion. This generating torque is comprared with the limit value of torsion stress of a screw 1. When the generating torque is smaller than the limit value, the screw is not broken and ordinary operation is performed. When the generating torque exceeds a certain rate of the limit value, the controller 7 turns off the command of an electromagnetic proportional valve 3 and the oil motor 2 is stopped to prevent the screw from being twisted and cut.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw breakage prevention device in an injection molding machine.

(Prior art) Conventionally, a molding material heated and fluidized in a heating cylinder is injected into a mold under high pressure, cooled and solidified or hardened therein, and then the mold is opened to take out the molded product. In injection molding machines, the resin supplied from the hopper to the heating cylinder is heated and melted by a heater installed in the heating cylinder, and as the screw retreats during the metering process, the resin moves forward and accumulates in front of the heating cylinder. It will be done.

FIG. 4 is a diagram showing a conventional screw rotation speed control device for an injection molding machine.

In the figure, reference numeral 1 denotes a screw that is arranged to move forward and backward within the heating cylinder, and 2 is an oil motor that is connected to the screw 1 and rotates when supplied with oil.

3 is an electromagnetic proportional valve for supplying and discharging oil to the oil motor 2, and the state shown in Figure 0, where the flow rate can be changed by an electric signal, is the neutral position, but it operates the solenoids at both ends. By the above oil motor 2
can supply and drain oil to.

A rotation detector 4 detects the rotation of the screw 1, and a detected value of the rotation detector 4 is sent to the controller 7. When the controller 7 receives the detected value, the above! The amount of oil supplied to the oil motor 2 is adjusted by issuing a command to the magnetic ratio side valve 3.

When starting injection molding in an injection molding machine with the above configuration, it is necessary to retract the screw and measure the amount. When the resin temperature is low, a large stress is applied to the screw head, which may cause breakage between the screw head and the screw body.

Therefore, in the screw of conventional injection molding machines, a "cold start prevention timer" is installed, and a sensor embedded in the heating cylinder detects the temperature of the resin. There is an interlock that prevents the metering operation from proceeding until a certain amount of time has elapsed.

(The problem that the invention seeks to solve!!!i) However,
In the screw breakage prevention device in the injection molding machine with the above configuration, the ink lock is activated by guessing without knowing the actual state of the resin, such as when the resin temperature is set incorrectly, so the screw cannot be completely protected. I can't.

Therefore, if the screw is attempted to be rotated when the resin is not completely melted during measurement, the screw may not be able to withstand the viscosity of the resin and may break.

The present invention solves the problem of the screw breakage prevention device in the conventional injection molding machine described above, and provides an injection molding machine in which the screw does not break when the screw is rotated in a state where the resin is not completely melted. The purpose of the present invention is to provide a screw breakage prevention device.

(Means for Solving the Problems) For this purpose, the screw breakage prevention device for an injection molding machine of the present invention includes an oil motor connected to the screw and for rotating the screw, and an oil motor on the suction side and the discharge side of the oil motor. It has a pressure sensor that detects pressure, and means that converts the difference between the detected values of the pressure sensor into torque generated by the oil motor.

A means is provided to compare the generated torque with a limit value of the torsional stress of the screw stored in advance in the controller, and the oil motor is stopped when the generated torque reaches a predetermined ratio of the torsional stress. ing.

(Function) According to the present invention, an oil motor is provided which is connected to the screw and rotates the screw as described above, and the oil motor is rotated during the metering process, and the screw is retracted to supply resin. Ru.

The oil motor includes a pressure sensor that detects the pressure on the suction side and the discharge side of the oil motor, and a means for converting the difference between the detected values of the pressure sensor into torque generated by the oil motor. and,
Means is provided for comparing the generated torque with a limit value of torsional stress of the screw stored in advance in the controller, and the oil motor is stopped when the generated torque reaches a set ratio of torsional stress. It has become.

Therefore, when the generated torque calculated from the difference in the detected values is low, the normal metering process is carried out, but when the generated torque becomes high and exceeds the set value, the electromagnetic proportional valve that adjusts the flow rate of the oil motor is A command is issued to stop the oil motor.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a screw breakage prevention device in an injection molding machine showing an embodiment of the present invention.

In the figure, reference numeral 1 indicates a screw that is arranged to move forward and backward within the heating cylinder, and reference numeral 2 indicates an oil motor that is connected to the screw 1 and rotates when supplied with oil.

Reference numeral 3 denotes an electromagnetic proportional valve for supplying oil to the oil motor 2, and the flow rate is made variable by an electric signal. Although the illustrated state is a neutral position, oil can be supplied to or discharged from the oil motor 2 by operating the solenoids at both ends.

A rotation detector 4 detects the rotation of the screw 1, and a detected value of the rotation detector 4 is sent to the controller 7. When the controller 7 receives the detected value, it issues a command to the electromagnetic proportional valve 3 to adjust the amount of oil supplied to the oil motor 2.

Here, pressure sensors 5 and 6 are disposed on the suction side and the discharge side of the oil motor 2 to detect the oil pressure.

Then, the difference between the detected values of the pressure sensors 5.6, that is, the pressure difference, is stored in the controller 7, and the torque generated by the oil motor 2 can be obtained by conversion from this pressure difference.

The torque generated by the oil motor 2 is determined by the pressure sensors 5 and 6.
It can be obtained from the detected value by the following equation.

T-1 engine (kg・-) 200 π P: Pressure difference 9o: Theoretical displacement is the volume The above generated torque is compared with the limit value of torsional stress of screw 1, and if the generated torque is smaller than the limit value, the screw Since there is no chance of breakage, normal operation is carried out.

The limit value of the torsional stress of the screw 1 varies depending on the material and shape, and this value is stored in the controller 7.

When the generated torque exceeds a certain percentage of the limit value, the controller 7 turns off the command to the electromagnetic proportional valve 3 to stop the oil motor 2 in order to prevent the screw from breaking.

Figure 2 is a diagram showing the flow rate command given to the oil motor.
FIG. 3 is a diagram showing a normal flow rate command.

Normally, as shown in Figure 3, the oil motor 2
In order to increase the rotation speed, the load suddenly increases during the first measurement, and the screw breakage prevention device cannot handle it in time, making it easy for the screw to break.Therefore, the rotation speed is gradually increased as shown in Fig. 2.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

For example, although an electromagnetic proportional valve is used in this embodiment, the same effect can be obtained by using a servo valve.

(Effects of the Invention) As described in detail above, the screw breakage prevention device for an injection molding machine of the present invention includes an oil motor connected to the screw and for rotating the screw, a suction side of the oil motor, and an oil motor connected to the screw for rotating the screw. It has a pressure sensor that detects the pressure on the discharge side, and a means for converting the difference between the detection values of the pressure sensor into the generated torque of the oil motor, and converts the generated torque into the torque of the screw stored in advance in the controller. The oil motor is stopped when the generated torque reaches a set ratio of torsional stress by comparing it with a limit value of torsional stress.

Therefore, even if the actual state of the resin is unknown, breakage of the screw can be reliably prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a screw breakage prevention device in an injection molding machine showing an embodiment of the present invention, FIG. 2 is a diagram showing a flow rate command given to an oil motor, and FIG. 3 is a diagram showing a normal flow rate command. FIG. 4 is a diagram showing a conventional screw rotation speed control device for an injection molding machine. DESCRIPTION OF SYMBOLS 1... Screw, 2... Oil motor, 3... Solenoid proportional valve, 4... Rotation detector, 5.6... Pressure sensor, 7... Controller. Patent Applicant Sumitomo Heavy Industries, Ltd. Sub-Agent Patent Attorney Makoto Kawago (1 other person) 77ri1tsuyu Figure 2 Hours → Passed away (SeC)

Claims (1)

[Claims] (a) an oil motor connected to the screw for rotating the screw; (b) a pressure sensor for detecting pressure on the suction side and discharge side of the oil motor; (c) the pressure (d) means for comparing the generated torque with a limit value of torsional stress of the screw; (e) means for converting the difference between the detected values of the sensor into a generated torque of the oil motor; (d) a means for comparing the generated torque with a limit value of torsional stress of the screw; A screw breakage prevention device for an injection molding machine, comprising means for stopping the oil motor when the oil motor reaches a certain percentage.