JP2882887B2 - Injection molding machine stringing prevention method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing stringing of a molded product which occurs when a mold is released after injection molding in an injection molding machine.

[0002]

2. Description of the Related Art The operation of a conventional injection molding machine will be described.
One cycle of an injection molding machine generally melts the resin in a heating cylinder, injects the molten resin into a mold cavity closed by a mold clamping device, cools the resin in the mold cavity, and then removes the mold. The cycle ends when the molded product is opened.

The tip of a screw cylinder including a nozzle of the above-mentioned injection molding machine has a structure shown in FIG. That is, in FIG. 5, a nozzle 11 is fixed to the tip of the screw cylinder 9 in which the screw 10 is inserted into the inner hole, and resin is injected from the nozzle 11 into the mold.
When the mold is opened after the resin in the mold cavity (not shown) has solidified, the sprue portion 8a of the molded product 8 has solidified as shown in FIG. However, the resin in the nozzle through hole 11a is still molten, and when the molded product is taken out at this time, the molded product 8
May be formed on the sprue portion 8a.

When the mold is opened and the cooled molded product 8 is taken out, the molten resin in the nozzle through-hole adheres to the sprue portion 8a of the molded product 8 left in the movable mold when the mold is opened. It may be pulled out in a thread form, which is a phenomenon called "stringing".

[0005]

When stringing occurs, the stringing resin adheres to the molded product 8, resulting in a defective appearance. The stringing phenomenon is a fatal defect particularly in the unmanned operation of an injection molding machine, but the state of stringing also changes with changes in the type of resin and molding temperature, and at present, no effective means has been found yet. is there.

According to the present invention, when the mold is released after injection molding, the screw in the screw cylinder is retracted in a direction opposite to the direction at the time of injection, thereby eliminating the "threading phenomenon".

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for injection molding of a molded article, in which after the plasticization and measurement of the molten resin, the mold is opened and at the same time the injection screw is retracted in the opposite direction to the injection . Suction the molten resin in the nozzle and apply tensile force to the resin
The Rukoto to cut the sprue portion given, obtained by such a stringing preventing is for a means for this problem solution.

[0008]

The resin in the nozzle is absorbed into the screw cylinder by retracting the screw for resin injection at the same time as the mold is opened. Due to this absorption, a tensile force acts on the molten resin in the stringing portion, whereby the sprue portion is cut and stringing is prevented.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an injection molding machine according to an embodiment of the present invention. In the figure, 1 is a mold clamping cylinder, 2 is a mold clamping ram, 4 is a fixed plate, and the fixed plate 4 is connected to a front part 1a of the mold clamp cylinder 1 by a tie bar 5. Movable board 3
Is fixed to the tip of the mold clamping ram 2 inserted into the mold clamping cylinder 1 and is guided by the tie bar 5 to move in the left-right direction in the figure. Reference numeral 6 denotes a movable mold fixed to the movable plate 3, and 7 denotes a fixed mold fixed to the fixed plate 4. Reference numeral 8 denotes a molded product, which is attached to the movable mold 6 and is removed from the mold cavity. Reference numeral 9 denotes a screw cylinder in which a screw 10 for melting and injecting the raw material is inserted into an inner hole, and reference numeral 11 denotes a nozzle fixed to the tip of the screw cylinder 9. The screw 10 is driven to rotate by a hydraulic motor 12 and is driven by an injection cylinder 13 in the left-right direction in the figure. Reference numeral 14 denotes a moving cylinder, which is a hydraulic device for moving an injection device including an injection cylinder, a screw cylinder, and a screw in the left-right direction in the drawing to bring the nozzle 11 into contact with the fixed mold 7 or to release the nozzle.

The mold clamping cylinder 1, the injection cylinder 13,
The hydraulic circuit for driving the moving cylinder 14 includes a switching valve 15 for switching the pressure oil to the mold clamping cylinder 1 and the injection cylinder 1.
Switching valve 16 for switching pressure oil to 3 and moving cylinder 1
4, a switching valve 17 for switching on and off the hydraulic oil to the hydraulic motor, a switching valve 19 for connecting and disconnecting the injection line and the mold clamping line, an injection speed, a mold clamping speed, and a screw rotation. Electromagnetic proportional flow control valve 20 for controlling speed, electromagnetic proportional relief valve 2 for controlling injection pressure
1, an electromagnetic proportional relief valve 22 for controlling the mold clamping pressure, an electromagnetic proportional relief valve 23 for controlling the back pressure, a large-capacity fixed capacity pump 24 and a small-capacity fixed capacity pump 25, and a pump for driving the pumps 24 and 25. An electric motor 26,
Further, in this embodiment, the switching valves 15, 1 of the hydraulic circuit are provided.
6, 17, 18, and 19, a sequence control for switching the process, a control device 30 for performing process control of an injection speed and an injection pressure predetermined by an electromagnetic proportional flow control valve 20 and an electromagnetic proportional relief valve 21, and a screw. And a position detector 31 for detecting the position of the position.

Next, a cycle of the injection molding machine according to the embodiment will be described with reference to FIG.

Mold closing step: This step is a step of closing the mold, and first, the switching valves 16, 17 and 18 are neutralized. At this time, when the electromagnetic proportional flow control valve 20 is set to an appropriate opening degree, the pressure oil from the fixed capacity pump 24 having a relatively large capacity and the pressure oil from the fixed capacity pump 25 having a relatively small capacity are merged. Mold clamping cylinder 1 via valve 15
Supplied to This determines the variable speed of the mold clamping cylinder 1 in the high speed range. The low speed range is determined by the discharge amount of the pump 25 alone.

Injection step: In this step, the switching valve 16 is switched while clamping the mold with the hydraulic pressure of only the small-capacity fixed capacity pump 25, and the hydraulic oil discharged from the large-capacity fixed capacity pump 24 is subjected to electromagnetic proportional flow. After passing through the control valve 20 and the switching valve 16, it is guided to the rear oil chamber of the injection cylinder 13,
The screw 10 is advanced to the left in the figure, and the resin melted in advance at the tip of the screw 10 is filled into the mold through the nozzle 11.

Measuring step: This step is a step of plasticizing the amount of the molten resin to be filled in the mold.
Rotate the screw 10 with the screw cylinder 9
Send to the front of At this time, the screw 10 retreats, and the pressure in the rear oil chamber of the injection cylinder 13 becomes equal to the electromagnetic proportional relief valve 2
A back pressure is given by setting the relief pressure of 3. The switching valve 17 is used to move the nozzle 11 forward and backward during one cycle.

Mold opening step: This step is a step of opening the mold to take out the molded product. FIG. 6 shows a sequence chart of the conventional mold opening step in this step, and FIG. 3 shows a sequence chart of the mold opening step according to the embodiment of the present invention. The normal mold opening process includes a low-speed release region where the mold is released at a low speed, a high-speed region where the mold is opened at a high speed, and a low-speed region where the speed is reduced to a low speed before stopping the mold. As shown in FIG. 6, in the conventional mold opening process, the solenoid b of the switching valve 15 is excited in the demolding low speed region and the re-low speed region, and when the switching valve 15 is switched, the small displacement fixed displacement pump 25 is used. Is supplied to the mold clamping ram 2 to open the mold at a low speed (left side in FIG. 1). In the high-speed range, the solenoid of the switching valve 19 is excited, the opening of the electromagnetic proportional flow control valve 20 is opened, and the set pressure of the electromagnetic proportional relief valve 21 is increased. Merges with the pressure oil from the small-capacity fixed displacement pump 25 to open the mold at high speed.

In the embodiment of the present invention, as shown in FIG.
The solenoid c of the switching valve 16
Is excited by a timer (not shown) in the control device 30 for a predetermined time, or is excited until the position detector 31 detects the amount of screw retreat and reaches a predetermined set value of the retreat amount. And a command to the electromagnetic proportional flow control valve 20 for supplying the pressurized oil to the injection cylinder 13 and retreating the screw 9 is added. The retreat speed of the screw 9 is controlled by the electromagnetic proportional flow control valve 20. It is supposed to be.

Next, the operation of the embodiment of the present invention will be described. Injection molding is completed and the mold releasing ram 2 starts moving to the left in a low-speed releasing region, and at the same time, the solenoid c of the switching valve 16 is turned off. When energized, the electromagnetic proportional flow control valve 20 opens its opening. As a result, pressure oil is supplied to the front oil chamber of the injection cylinder 13, and the screw 9 is forcibly retracted. FIG. 4 shows an enlarged view of the nozzle 11 at this time. As is clear from FIG. 4, the resin in the nozzle 11 is sucked by the retreat of the screw 9 to the right at the same time as the sprue portion 8a moves to the left, so that a tensile force is applied to the resin. Since this tensile force has the maximum tensile stress at the minimum cross-sectional area of the nozzle through hole 11a, the sprue portion is cut at this portion, and the threading portion does not occur as in the sprue portion 8a of FIG.

In general, the melt viscosity of the threading portion changes depending on the type of resin and the molding temperature, and the state of stringing changes. The adjustment is made by adjusting the pulling force, that is, the screw retreat amount and the screw retreat speed, according to the above. Generally, it is preferable to adjust the speed by setting the retreat amount to about 1 to 3 mm. Although the apparatus of this embodiment has been described as a direct pressure type mold clamping apparatus, the present invention is not limited to this, and the effect of preventing stringing can be obtained by a similar operation in a toggle type or an electric mold clamping apparatus.

[0019]

As described above in detail, according to the present invention, at the time of mold release after injection molding, the injection screw in the nozzle is rapidly retracted, and the molten resin in the nozzle is sucked to remove the resin.
Since it so that to cut the sprue portion giving a tensile force to the fat, stringiness can be effectively prevented. Also, by changing the screw retreat amount and the retreat speed in response to changes in the type of resin and the molding temperature, excellent effects such as easy adjustment of stringing prevention can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a cycle of the injection molding machine of the present invention.

FIG. 3 is a sequence chart of a mold opening process of the present invention.

FIG. 4 is a sectional view of the tip of a screw cylinder including the nozzle of the present invention.

FIG. 5 is a sectional view of a tip portion of a screw cylinder including a conventional nozzle.

FIG. 6 is a sequence chart of a conventional mold opening process.

[Explanation of symbols]

 Reference Signs List 1 mold clamping cylinder 9 screw 10 screw cylinder 11 nozzle 13 injection cylinder 30 control device 31 position detector

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Claims (1)

(57) [Claims] At the time of injection molding of a molded article, after the plasticization and measurement of the molten resin, the mold is opened, and at the same time, the injection screw is retracted in a direction opposite to the injection to absorb the molten resin in the nozzle.
Arguments to the Rukoto to cut the sprue portion giving a tensile force to the resin, stringing prevention method for an injection molding machine, characterized in that as the stringing preventing.