JPH0722946B2 - Air-venting device for plastic mold - Google Patents

Description

The present invention relates to an air vent device for a plastic molding die.

[Conventional technology]

When the plastic is injection-molded by the molding die, if the air in the die cavity is not sufficiently removed, the air remains in the cavity and a molded product has a lacking portion. Conventionally, in order to prevent this, an air reservoir is provided outside the product shape portion on the parting surface of the mold. In Japanese Utility Model Laid-Open No. 55-33774, a knock pin for releasing a product is arranged in the air reservoir, and the air and gas in the cavity are forcibly discharged from the space around the knock pin. Has been done.

In Japanese Utility Model Laid-Open No. 60-105120, an air vent passage communicating from the die cavity to the outside of the die is formed, and an air vent valve is installed at the opening of the passage to the cavity by a spring to bias the air vent valve. The air bleeding valve of the molding die is
Further, in Japanese Patent Laid-Open No. 60-228118, a hole facing a cavity of a movable die is provided, a pin is slidably inserted into the hole, a closing portion is provided at the tip of the pin, and vacuum suction extending to the vicinity thereof There is described an injection molding method in which a passage is formed, a closed portion of a pin is projected into the cavity in a mold closed state, air in the cavity is vacuum-sucked, and the pin is retracted to inject a resin into the cavity.

In addition, in Japanese Utility Model Publication No. 60-18905, a shape memory alloy valve is installed near the runner end of the molding die to remove the gas in the cavity at the time of injection molding. A molding die degassing mechanism has been proposed which closes the valve and holds the resin in the die cavity.

[Problems to be solved by the invention]

Recently, Metton resin has been used as a plastic material for rim products and automobile bumpers instead of metal materials.

This Metton resin has extremely high fluidity and mixes two liquids for injection molding. It reacts when the two liquids are mixed to generate heat, and has the property of further reaction when exposed to air. ing. Metton resin has a high fluidity and enters the gap of 0.02 mm. Therefore, in the case where air is exhausted from the gap (0.05 to 0.1 mm) on the outer periphery of the conventional knock pin, the Metton resin enters the gap that discharges this air. However, it reacts with air and solidifies by reacting with it, closing the voids, and making it impossible to bleed air during the next molding.

For example, when a bumper of an automobile is injection-molded with Meton resin, a hollow portion where the material is not sufficiently filled occurs in the central window portion, which makes it very difficult to repair this product later.

In order to solve this problem, in each of the publications described above, an air vent passage communicating from the mold cavity to the outside of the mold is formed, and an air vent valve such as a shape memory alloy valve is installed in the opening to the cavity, There is disclosed a technique in which the gas in the cavity is removed during injection molding and the air vent valve is closed when the resin is filled so that the resin is retained in the mold cavity. However, when molding a resin with extremely high fluidity such as Meton resin, the resin enters the block surface of the air vent valve or the air vent passage and solidifies during molding, blocking the air vent passage and Sometimes it may not be possible to bleed air.

The present invention automatically cleans the air vent passage when the movable die is opened and the molded product is taken out after the molding, so that the air vent function is not impaired even if the molding is continuously performed. The purpose is to prevent the occurrence of a flesh portion.

[Means and Actions for Solving Problems]

According to the present invention, a moving die is provided with an air vent hole which communicates with a cavity, a valve shaft having a valve head at a tip portion is communicated with the air vent hole, and the valve head is held in an open state by a spring to support the air vent. A part of the hole has a small diameter to form a narrow gap with the valve shaft, a cleaning tool is attached to the valve shaft at an outer position of the narrow gap portion, and the other end of the valve shaft is installed in a moving mold. It is an air bend device for a plastic molding die that faces the movement path of an extrusion plate.

During injection molding, the air and gas in the cavity are pushed by the inflowing molding material and are discharged from around the valve head to the air vent hole. Close the hole.

After the molding, when the movable mold is opened to release the product, the valve shaft pushes the spring with the pushing plate to push it toward the cavity side, and the cleaning tool attached to the lube shaft removes the resin adhering to the air vent passage.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a partial vertical cross-sectional view of a mold in a closed state, which is an example of forming a bumper for an automobile.

The lower mold 1 is a fixed mold, the upper mold 2 is a movable mold, and is fixed to a reference plate 5 via a guide 4, and the reference plate 5 is moved up and down by a molding machine. In the illustrated state in which the upper mold 2 is lowered and the mold is closed, a cavity 3 which is a molding shape portion is formed between the lower mold 1 and the upper mold 2.

A mixing head is applied to an injection port (not shown) connected to the cavity 3 to inject the Meton resin in which the liquids A and B are mixed. The Meton resin injected into the cavity 3 flows in the a, b, and c of the figure while pushing the air in the cavity 3, and enters the air pool d.

An enlarged view of the vent valve is shown in FIG. 2 (B). A valve head 13 is attached to the tip of the valve shaft 10 by a fixing means such as a screw. The valve head 13 is made of bimetal or shape memory alloy, and its outer diameter is expanded when heated.

The lower portion of the air vent hole 2a provided around the valve shaft 10 is a small diameter portion 2b, and the gap f between the small diameter portion 2b and the valve shaft 10 shown in FIG. 2C is about 0.02 mm.

At the stage where the molding material flows a, b, c, d, the air pushed by the molding material passes through the narrow gap e on the outer periphery of the valve head 13 and the gap f of the small diameter portion and is discharged from the air vent hole 2a. Since the Metton resin has good fluidity and the extrusion pressure of the molding material is weak, the air does not enter the gap f from the outer periphery e of the valve head 13 but only the air is initially discharged.

With the passage of time, the Meton resin comes into contact with air, and with the passage of time, a reaction is caused to heat the valve head 13 by an exothermic reaction. The valve head 13 expands and closes the slit e as shown by the broken line in FIG. 2 (B). Therefore,
The air vent hole 2a discharges the air in the cavity 3 to the outside of the mold until just before the valve head 13 closes the passage, so that air is not accumulated in the mold and the molding material enters after the valve head 13. As a result, the air vent function is not impaired, so that the product is free from wall thickness.

When the molding is completed and the mold is opened, the upper mold 2 is raised by the reference plate 5 through the guide 4. When the upper die 2 rises to the top dead center position, the air cylinder 7 fixed to the upper die 2 operates to lower the piston 7a and lower the push plate 6 fixed thereto. On the extruded plate 6, at the tip,
Since the thrusting rod 8 having the head portion 8a forming the shape portion of the mold cavity 3 is fixed, the molded product is transferred to the upper mold 2
And extruded from the mold. In addition, the flat portion 8b is provided on the thrust rod 8.
Is provided and is engaged with the anti-rotation plate 9 to prevent its rotation.

When the push-out plate 6 descends from the top dead center position P ₁ and reaches the P ₂ position, it comes into contact with the head 10b of the valve shaft 10 and pushes it down to the P ₃ position. Guide pin 10a on the valve shaft 10
Is provided, and the spiral slit 11 of the cover guide 11 is provided.
Since it is designed to engage with a, the valve shaft 10
Moves down while compressing the spring 12. As shown in FIG. 2 (D), the metal brush 10b is attached to the tip of the valve shaft 10.
Such a cleaning tool is fixed to remove burrs and fine dust when passing through the small diameter portion 2b of the air vent hole. The cleaning tool may be a tool having a blade such as a file or a cutter.

In FIG. 1, L ₁ indicates the stroke of the valve shaft 10, and L ₂ indicates the stroke of the pushing plate 6.

When the guide pin 10a of the valve shaft 10 is engaged with the spiral slit 11a shown in FIG. 1, the cleaning tool 10b rotates when passing through the small diameter portion 2b of the air vent hole. Cleaning tool
When the movement of 10b is made straight, the guide pin 10b is provided with a linear slit 11 of the gabber guide 11 shown in FIG. 2 (A).
Engage with b.

In order to close the mold, the air cylinder 7 is operated, the piston 7a is raised to bring the pushing plate 6 to the top dead center position P ₁ , and the reference plate 5 is lowered to the state shown in FIG.

In this embodiment, when injection molding is performed by using a molding material having an extremely high fluidity such as Meton resin, air and gas in the mold cavity can be sufficiently discharged, and the air vent is introduced by the entrance of the molding material. The function can be maintained because the function is not impaired and the air vent passage is cleaned every time the product is released from the mold after molding.

〔The invention's effect〕

The present invention removes gas in the cavity during injection molding,
When the resin is filled, the air vent valve is closed to keep the resin inside the mold cavity, so that gas accumulation in the mold cavity can be prevented and the molding resin enters the air vent passage and solidifies. When this is done, the air vent passage is automatically cleaned every time it is released from the mold, so even if molding is performed continuously, the air vent function will not be impaired, and it will be possible to prevent the occurrence of underfilled parts in the product. it can.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional view showing an embodiment of the present invention, FIG. 2 is a view showing a main part of FIG. 1, and FIG. 2 (A) is a valve shaft viewed from the Z direction of FIG. An external view of the head, FIG. 2 (B) is an enlarged cross-sectional view of the vent valve, and FIGS. 2 (C) and 2 (D) are respectively X- in FIG. 2 (B).
It is sectional drawing which follows the X-ray and the YY line. 1: Lower mold 2: Upper mold, 2a: Air vent hole 3: Mold cavity 6: Extrusion plate 7: Air cylinder 10: Valve shaft 13: Valve head

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-228118 (JP, A) Actual development 60-105120 (JP, U) Actual public 60-18905 (JP, Y2) Actual public 61- 40534 (JP, Y2)

Claims (1)

[Claims] 1. A moving die is provided with an air vent hole communicating with a cavity, and a valve shaft having a valve head at its tip is inserted into the air vent hole to support the valve head in an open state by a spring. A part of the air vent hole has a small diameter to form a narrow gap with the valve shaft, and a cleaning tool is attached to the valve shaft at a position outside the narrow gap part, and the other end of the valve shaft is moved. An air vent device for a plastic molding die, which is exposed to the movement path of an extruded plate installed in the die.