JPS6220010B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molding method using synthetic resin as a material.

In-line screw type injection molding machines,
When the screw is rotated with the nozzle kept in contact with the mold or closed by a valve, as the molten material is stored at the front of the injection cylinder, the screw is moved back by the pressure of the material. Generally, the above process is called material metering or plasticization.
The retracting screw activates a limit switch, and when the screw stops rotating, it is assumed that metering or plasticization is complete. Therefore,
The amount of material accumulated can be arbitrarily determined by changing the position of the limit switch.

Injection of material by the advancement of the screw is performed by a signal generated when the mold is closed, and the control is either temporally by a timer or by adjusting the amount of movement or position of the screw using the screw rotation stop position as a reference point. This was done by means of detecting this using a limit switch.

With this conventional control means, no consideration is given to the backflow of material that occurs during injection, and therefore there is a problem in injecting the measured amount of material into the mold without shortage. This is because, regardless of the presence or absence of a valve body to prevent backflow, some of the material at the front of the cylinder will flow backwards as the screw moves forward, and material will be injected in an amount equal to the amount of backflow. That's because there isn't. In general, for products equipped with a check valve, the backflow of material is considered to be extremely small and not to have a major effect on injection, but the check valve closes when the screw moves forward. Material flowing back from between the screw and the screw can sometimes have a large effect on injection, and since the back flow varies from injection to injection and lacks consistency, it is extremely difficult to measure by taking the back flow into account. It is.

Also, when molding materials that tend to be inconvenient when using a check valve, for example, composite materials such as hard vinyl chloride resin, glass fiber-containing resin, thermosetting resin, etc., when the injection cylinder starts the injection stroke. The material density distribution in the screw reed from the tip of the screw to the material inlet is densest at the tip of the screw, and tends to gradually decrease as it approaches the material inlet, and is the same every time. It is said to be extremely difficult to achieve this condition.
Therefore, during injection, the material flows back along the screw lead until the material pressure at the front of the screw and the material pressure in the screw lead become equal. As a result, the injection amount and pressure are significantly reduced compared to the case with a check valve, which greatly affects injection.

In this invention, after measurement is completed, the screw is advanced to a predetermined position and the accumulated material at the front of the cylinder is temporarily pressurized to stabilize the material volume, and then the screw is moved until the pressure of the entire material reaches the set value. After the pressure has been removed for the required time, the screw position is set as the reference point for the injection stroke.
Since then, we have attempted to provide a new method and device for controlling the injection speed, injection pressure, etc. step by step to eliminate the drawbacks of the conventional backflow described above, and to further ensure the filling of material into the mold. It is something to do.

However, this invention measures a predetermined amount of material into the front part of the cylinder by rotating and retracting the screw, and then moves the screw forward to apply pressure that completely closes the valve body if the screw is equipped with a check valve. In addition, if there is no check valve, apply pressure such that the density within the screw reed is high enough to prevent the material from flowing back across the entire width during the injection stroke, and then remove the pressure and stop the injection process.
Further, using the screw position after the elapse of the required time as a reference point, after closing the mold, in the case of a nozzle with a valve, the valve body is opened and the screw is advanced to apply injection pressure to the material and inject it into the mold. Changes in the position of the screw as it moves forward are detected electrically or mechanically, and the screw is automatically controlled when the screw position reaches a predetermined secondary injection pressure switching position or stop position. .

In this invention, confirmation when the screw reaches the reference point from the metering completion position can be made by means of detecting the internal pressure of the cylinder with a timer or pressure switch, by means of detecting the internal pressure of the material with a resin pressure gauge, or by moving the screw. Means for detecting stoppage by electrically sensing it, etc. can be used.

Injection devices to which this invention can be applied are not limited to those having a check valve as described above. In addition, when applied to an injection device that is equipped with a check valve but does not have a nozzle closing valve, the process of closing the check valve is performed by cooling and solidifying the molded product in the mold in the closed state. and when the nozzle is touched.

Further, the present invention will be explained in detail with reference to illustrated examples.

In the embodiment shown in FIG. 1, the screw is electrically controlled, and 1 is an injection cylinder, 2 is a screw, and its rear part is connected to an injection ram 4 of a hydraulic cylinder 3. Reference numeral 5 designates a movement amount control device for the screw 2, which includes a detection unit 51 equipped with a head b in contact with a scale a attached to move together with the injection ram 4, a movement amount detection and conversion device 52, a comparison device 54, and a setting device 53. Consists of electrically connected devices.

The above-mentioned scale a consists of a magnetic material with a lattice-shaped magnetization pattern recorded by recording a sine wave at a certain wavelength as a magnetic scale, and the head b detects the above-mentioned magnetic scale and outputs a sine wave. generate.

The movement amount conversion detection device 52 receives the electrical signal from the detection unit 51 and generates a pulse signal proportional to the movement amount.

The comparison device 54 compares the output of the movement amount conversion detection device 52 and the signal from the setting device 53, and outputs an output signal when a set value is reached.

The setting device 53 is a device for setting a target movement amount, and generates a setting signal.

Next, the injection molding method of the present invention will be explained using an injection molding machine equipped with a check valve 6 and a nozzle opening closing valve 7 as an example.

First, the nozzle port is closed using the nozzle port closing valve 7, and then the screw is rotated. The screw is moved to the second position by the pressure of the material stored in the front part of cylinder 1.
When the metering is completed by retreating to the position shown in the figure, pressure oil is supplied to the hydraulic cylinder 3 by the action of a timer, and the screw 2 is advanced to temporarily pressurize the material. Due to this pressurization, a part of the material pushes the check valve 6 back from the screw head side, and the check valve 6 blocks the material passage to prevent backflow of the material. When the check valve 2 reaches the closing position due to material pressure, the hydraulic pressure supply to the hydraulic cylinder 3 is temporarily cut off, and the screw 2 is stopped. By stopping the screw 2, there will be no more local compression of the material than necessary, and even if the material pressure is extremely high on the screw side and low on the nozzle side during pressurization, the pressure will be equalized over time. Accurate capacity can be determined under constant pressure.

Next, the material is injected using the stop position of the screw 2 as a reference point. That is, the screw 2 is stopped until the time required for the pressure distribution of the entire material to reach a certain constant value (set time) has elapsed, and when the set time has elapsed (as shown in Figure 3) position), a measurement start signal is given to the movement amount conversion detection device 52 to activate it, and the screw reference position is set.

Next, an injection signal sent from the mold clamping device side opens the closing valve 7 at the nozzle port, and at the same time, the waiting screw 2 enters the injection stroke by hydraulic pressure.
The internal pressure of the cylinder 1 is switched to the injection pressure, and the screw 2 moves forward. As the screw 2 moves forward, an electric signal proportional to the amount of movement is generated in the movement amount detection and conversion device 52. The electric signal and a desired setting signal are then compared by a comparator 54, and when a match is found, an output signal for switching the injection pressure to the secondary pressure is output from the comparator 54.

When the injection of a predetermined amount of material is completed by the advance of the screw, the nozzle opening is closed, the screw 2 rotates and starts metering again, and retreats further backward from the reference point to finish metering. Move on to the next injection stroke.

As described above, this invention applies a certain pressure to the weighed material at the front of the cylinder, then stops the screw to eliminate variations in material volume due to backflow, and then stops the screw by increasing the pressure on the screw. The injection process is performed until the pressure of the entire material reaches the set value, and then the injection speed, injection pressure, etc. during the injection process can be controlled step by step using the screw position after the time has elapsed as a reference point. Therefore, it has the following effects.

(1) Since the screw is temporarily stopped after pressurizing the material, dynamic errors are eliminated, the volume of the material can be determined more accurately, and the material is stabilized, so a molded product with good molding condition can be obtained.

(2) After pressurizing the material accumulated at the front of the cylinder,
Since the injection is controlled based on the volume under constant pressure, the measurement does not require as much accuracy as compared to the conventional method, and the accumulated material changes somewhat due to fluctuations in screw back pressure during plasticization. However, it is not a particular problem.

(3) A method of controlling the injection speed and injection pressure by varying them in several stages according to the screw position during the injection process to prevent flow marks, weld lines, etc., using the screw position of this invention as a reference point. If it is controlled, even greater effects can be expected.

(4) If the check valve is damaged or caught by a foreign object such as metal during operation, the check valve loses its function and cannot be formed stably. However, when this invention is used, it is possible to It is also possible to issue an alarm or set the machine to stop when the screw moves, so abnormal check valve operation can be quickly discovered during automatic operation, and defective products can be prevented. It can also be prevented.

[Brief explanation of the drawing]

The drawings are for explaining the injection molding method of the present invention, and FIG. 1 is a schematic cross-sectional view of an injection device equipped with an electric control device, and FIG. 2 is a front view of the cylinder showing the screw position when metering is completed. FIG. 3 is a sectional view of the front part of the cylinder when the screw is stopped at the reference point. DESCRIPTION OF SYMBOLS 1...Cylinder, 2...Screw, 5...Movement amount control device, 6...Return valve, 7...Nozzle opening closing valve, 51...Detection section, 52...Movement amount detection conversion device, 53... ...setting device, 54...comparison device, a...
...Scale, b...Head.

Claims (1)

[Claims] 1 After measurement is completed, move the screw forward to a predetermined position without rotating, temporarily pressurize the material accumulated at the front of the cylinder to stabilize the material volume, and then move the screw until the pressure of the entire material reaches the set value. An injection molding method characterized in that the injection pressure, injection speed, etc. in the injection stroke are controlled using the screw position after the time required to reach the pressure as a reference point.