JPH03221426A - Injection molding method - Google Patents

Abstract

PURPOSE:To reduce fluctuation of the amount of resin filled into a mold by advancing a screw in a state wherein a valve nozzle is previously closed before injection after weighing is completed and raising the pressure of the front part of an injection cylinder and then opening the valve nozzle to start injection and advancing the screw at the prescribed amount from a point of this time. CONSTITUTION:When a screw 4 is slightly advanced in a state wherein a valve nozzle 6 is closed from the state such as molten resin is weighed and accumulated in an injection cylinder 3 of the tip of the screw 4, the resin weighed and accumulated in the tip is allowed to reversely flow to the direction shown in an arrow from a passage 81 of resin. A counter-flow preventive ring 8 closes the passage 81 in the advance position t1 and the pressure of resin is suddenly changed. A controlling device 14 controls an injection molding machine 1 so that the valve nozzle 6 is allowed to abut against the inflow port 20 of a mold 19 at a point of time when the screw 4 reaches the position t1. When the valve nozzle 6 is allowed to abut against the inflow port 20, the valve 61 is opened and the resin weight and accumulated in the tip part of the injection cylinder 3 is injected into the mold 19. When the position of the screw 4 reaches the prescribed position measured by a screw position detector 10 together with advance, the controlling device 14 is stopped in the advance and stoppage position t3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection molding method used for molding synthetic resin. Specifically, the present invention relates to an injection molding method using an injection molding device equipped with an injection cylinder provided with a valve nozzle and a screw equipped with a backflow prevention ring on the screw head.

(Prior Art) Conventionally, as shown in FIG. 5, the injection molding method used for molding synthetic resin includes an injection cylinder b equipped with a valve nozzle a, and a backflow prevention ring on the screw end C. A method of molding using an injection molding device comprising a screw e equipped with a screw d is known.

In this injection molding device, when the screw e is retreated,
The backflow prevention ring d moves slightly in front of the screw e, and the resin passage f formed between the backflow prevention ring d and the screw head C becomes in communication. Resin flows from this resin passage f into the cylinder b on the distal end side of the screw head C, and can be measured and stored. When filling the cavity of a mold with resin, the tip of a valve nozzle a is brought into contact with an inlet g of the mold to open a valve h and the screw e is advanced to fill the mold. In this case, when the screw e moves forward, the metered and accumulated resin presses the backflow prevention ring d toward the rear of the screw e.
The backflow prevention ring d closes the resin passage f, and the backflow of a predetermined amount of resin is prevented.

(Problems to be Solved by the Invention) However, in the conventional injection molding method described above, in continuous molding, the melted state of the resin measured for each shot is not necessarily constant but changes. Therefore,
Since the timing of closing the resin passage f of the backflow prevention ring d at the start of injection varies from molding cycle to molding cycle, the amount of resin injected into the mold fluctuates, resulting in poor weight and dimensional accuracy of the molded product. There was a problem.

The present invention was made to solve the above problems, and its purpose is to provide an injection molding method that makes it possible to reduce fluctuations in the amount of resin filled into a mold. .

(Means for Solving the Problems) The injection molding method of the present invention is a method of molding using an injection molding device equipped with an injection cylinder provided with a valve nozzle and a screw equipped with a backflow prevention ring on the screw head. After measurement is completed and before injection, advance the screw with the valve nozzle closed to increase the pressure at the front of the injection cylinder, then open the valve nozzle to start injection, and when the valve nozzle is opened. The mold is characterized by filling the mold with resin by advancing the screw by a predetermined amount.

(Function) In the injection molding method configured as described above, when the screw is advanced with the valve nozzle closed after metering is completed and before injection, the backflow prevention ring is activated and the metered amount is accumulated at the front of the cylinder. The backflow of the resin is stopped and the pressure increases. When the screw reaches a position where the pressure increases, the valve nozzle is opened and the screw is advanced by a predetermined amount, thereby filling the mold with the predetermined amount of resin.

(Example) Hereinafter, an example of the injection molding method of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic diagram of an apparatus used in the injection molding method according to the present invention.

In the figure, 1 is an injection molding device, 2 is a hopper 3 is an injection cylinder, and 4 is a screw.

In the injection molding apparatus 1, when the screw 4 is rotated in the opposite screw direction of the flight 41 in the metering process, the raw resin supplied from the hopper 2 is melted and plasticized, and the raw resin is fed to the front of the injection cylinder 3 and accumulated while the screw 4 is rotated. is designed to retreat, and in the injection process, the retreated screw 4 is advanced by a hydraulic ram mechanism 5 to inject molten resin from a valve nozzle 6 provided at the tip of the injection cylinder 3. .

Further, a backflow prevention ring 8 is inserted into a screw head 7 provided at the tip of the screw 4. The backflow prevention ring 8 closes or opens the resin passage 81 formed between the backflow prevention ring 8 and the screw head 7 as the screw 4 advances and retreats, as shown in FIGS. 2(a) to (C). As shown in FIG. 2(C), when the screw 4 rotates and retreats to measure and accumulate resin in the front part of the injection cylinder 3, the resin passage 81 is opened and the screw is inserted from the screw 4 side. The resin is caused to flow into the tip side of the head 7, and conversely, as shown in FIG. 2(b), when the screw 4 moves forward, the resin passage 81 is closed to prevent the resin from flowing back.

Furthermore, a pressure sensor 9 is provided at the front of the injection cylinder 3 to measure the resin pressure at the front of the injection cylinder 3, and a screw position detector constituted by a potentiometer or the like is also provided. 10, the forward and backward positions of the screw 4 are measured. The measured value measured by the pressure sensor 9 is output as a control signal to the control device 14 of the injection molding machine 1 via the pressure signal amplifier 11, the differentiator 12, and the signal generator 13, and is also output to the control device 14 of the injection molding machine 1, which will be described later. It is now output to . Further, the measured value measured by the screw position detector 10 is inputted to the calculator 15 together with the set value inputted by the data input device 16 and the pressure signal from the signal generator 13 mentioned above, and is calculated by the calculator 15. The calculation result is output as a control signal to the control device 14 that controls the injection molding machine 1 via the output signal generator 17.

In the figure, reference numeral 19 denotes a mold, and the injection port 20 of the mold 19 comes into contact with the tip of the valve nozzle 6.

Next, the injection molding method of the present invention using a ridge injection molding apparatus will be described.

FIG. 2(a) shows a state in which the screw 4 is stopped at the retracted position t0, and molten resin is metered and accumulated in the injection cylinder 3 at the tip of the screw 4.

In the injection process, when the hydraulic ram mechanism 5 is operated with the valve nozzle 6 closed and the screw 4 is slightly advanced, the resin stored at the tip flows backward from the resin passage 81 in the direction of the arrow S. As shown in FIG. 2(b), the backflow prevention ring 8 closes the resin passage 81 at the forward position tl. At this time, the resin pressure measured by the pressure sensor 9 does not vary between the retreat position t0 and the position t1 where the resin passage 81 is closed by the backflow prevention ring 8, as shown in FIG. Position 1. The resin pressure changes rapidly.

The resin pressure measured by the pressure sensor 9 and shown in FIG. 3 is input to the differentiator 12 via the pressure signal amplifier 11. In the differentiator 12, the resin pressure at position lt is the fourth
As shown in the figure, the position t1 of the inflection point of the resin pressure fluctuation is detected from the differentiated value, and a control signal is sent to the control device 14 via the signal generator 13 at the time when this position t1 is detected. .

The control device 14 is configured so that the screw 4 is in position 1. At the point in time, the injection molding machine 1 is controlled so that the valve nozzle 6 comes into contact with the inlet 20 of the mold 19. When the valve nozzle 6 comes into contact with the inlet 20 of the mold 19, the pulp 61 opens and the resin metered and stored at the tip of the injection cylinder 3 is injected into the mold 19.

Meanwhile, during this time, the position of the screw 4 is being measured by the screw position detector 10 as the screw 4 moves forward. This measured value is input to the calculator 15 along with the set value manually input by the data input device W16 and the pressure signal from the signal generator 13 described above.

When the resin pressure fluctuation signal is input from the signal generator 13, the calculator 15 calculates the amount of advance W of the screw 4 measured at the position t1 at the time of manual input. The measured value is subtracted from the amount of advance W being measured. This subtraction (!(w-wo) is compared with the set value W of the data human power device 16. If it matches the set value w1 of the data human power device W16, a control signal is sent to the control device 14 via the output signal generator 17. is sent.

The control device 14 stops the screw 4 from moving forward at the forward stop position t3, switches from the injection process to the pressure holding process, and controls the pressure holding.

After the pressure is maintained, the hydraulic ram mechanism 5 is operated to retract the screw 4 to the state shown in FIG. 2(a), thereby completing one cycle of injection molding. In this case, when the screw 4 retreats, the backflow prevention ring 8 moves slightly in front of the screw 4 as shown in FIG. 2(C), and the resin passage 81 opens. Through this resin passage 81, the resin is metered and accumulated in the front part of the injection cylinder 3 while being plasticized.

When 1000 shots were continuously injection molded using the above injection molding method of the present invention, the average weight of the obtained molded product was 137.2 g, but the weight variation was ±0.25%.
Met. However, the average weight of the molded products obtained by the conventional method was 137.2 g, and the weight variation was ±1.30%.

(Effects of the Invention) Since the injection molding method of the present invention is configured as described above, there is little variation in the amount of resin injected into the mold in each molding cycle, and the weight and dimensional accuracy of the molded product are improved. do.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an injection molding apparatus used in the injection molding method of the present invention, and FIGS. 2(a) to (C) are explanatory views of the operation of the screw of the injection molding apparatus shown in FIG. Second
Figure (a) is a cross-sectional view showing the state in which the screw has retreated and stopped, Figure 2 (b) is a cross-sectional view showing the state in which the screw has moved forward and the backflow prevention ring has closed the resin passage, Figure 2 (C)
is a cross-sectional view showing the state of the metering process after retracting from the forward stop position, Figure 3 is a diagram showing the change in resin pressure in the front part of the injection cylinder during injection molding, and Figure 4 is the change in resin pressure in Figure 3. FIG. 5 is a partially cutaway cross-sectional view of an injection molding apparatus illustrating a conventional example. Explanation of symbols 1. Injection molding device, 3. Injection cylinder 4. Screw 5. Hydraulic ram mechanism, 6. Valve nozzle, 7.
...Screw head, 8..Backflow prevention ring, 81.
- Resin passage, 9... Pressure sensor 10... Screw position detector, 11... Pressure signal amplifier, 12... Differentiator, 13... Signal generator, 14... Control device, 15...
Arithmetic unit, 16...Data human power device, 17...Output signal generator, 19...Mold, 20...Injection port 20° Figure Figure Figure Figure Figure Figure

Claims (1)

[Claims] 1. A method of molding using an injection molding device equipped with an injection cylinder equipped with a valve nozzle and a screw with a backflow prevention ring attached to the screw head, in which the valve nozzle is closed before injection after completion of metering. In this state, the screw is advanced to increase the pressure at the front of the injection cylinder, and the valve nozzle is opened to start injection. From the point when the valve nozzle is opened, the screw is advanced a predetermined amount to inject the resin into the mold. An injection molding method characterized by filling.