JPH0698643B2 - Molding machine for synthetic resin moldings - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding apparatus for molded articles made of synthetic resin, and more particularly to an improvement of a molding apparatus using an injection molding method.

[0002]

2. Description of the Related Art Under the application of an injection molding method, after a molten synthetic resin is injected into a molding cavity to mold a molded body, a pressure for compensating for shrinkage, that is, a holding pressure must be applied to the molded body. I won't.

Conventionally, the holding pressure is obtained by setting a high injection pressure of the molten synthetic resin.

[0004]

However, according to the conventional apparatus, when the molded body is large, the injection pressure is increased accordingly. Therefore, in order to suppress the occurrence of flash, the mold clamping force is increased. There is a problem that the equipment cost for that purpose must be increased.

In view of the above, the present invention provides the above-mentioned molding apparatus which makes it possible to obtain a sufficient holding pressure without increasing the injection pressure of the molten synthetic resin, thereby suppressing the occurrence of burrs and having a low equipment cost. The purpose is to provide.

[0006]

A molding apparatus for a synthetic resin molded body according to the present invention comprises a molding die having a molding cavity, a gate communicating with the molding cavity, and an overflow chamber communicating with the molding cavity. A gas blowing mechanism for blowing gas into the molten synthetic resin to form a hollow portion in the molten synthetic resin injected into the molding cavity through the gate to form a hollow molded body; In order to apply a holding pressure to the pressure chamber, a holding pressure applying mechanism for blowing gas into the overflow chamber is provided.

Further, the molding apparatus for a synthetic resin molded body according to the present invention includes a molding die having a molding cavity, a gate communicating with the molding cavity and an overflow chamber communicating with the molding cavity, and the molding die through the gate. In order to apply a holding pressure to the solid molded body made of the molten synthetic resin injected into the molding cavity, a holding pressure applying mechanism for injecting gas into the overflow chamber is provided.

[0008]

1 to 3 show an embodiment of a molding apparatus, which is used for molding a hollow molded body.

In FIG. 1, a molding die 1 is composed of a fixed die 2 and a movable die 3, and a molding cavity 4 having a cylindrical shape, a gate 5 and a cavity communicating with one end of the cavity 4 by the dies 2 and 3. An overflow chamber 7 that communicates with the other end of 4 via the outflow passage 6 is formed. The gate 5 communicates with an injection nozzle (not shown). The cross-sectional area of the outflow passage 6 is set to be smaller than the cross-sectional area of the cavity 4.

The movable mold 3 is provided with a gas blowing mechanism 8 for blowing a high pressure gas into the molten synthetic resin so as to form a cavity in the molten synthetic resin injected into the molding cavity 4 through the gate 5. There is. The gas blowing mechanism 8 is configured as follows.

A gas blowing hole 9 is formed near the gate 5 of the movable die 3, and a first hydraulic cylinder 10 for opening and closing the blowing hole 9 is attached to the movable die 3. First hydraulic cylinder 1
The cylinder body 11 of 0 has a small diameter hole a ₁ , a medium diameter hole a ₂ and a large diameter hole a ₃ which are sequentially arranged from the side of the blow hole 9 toward the outside of the movable mold 3 . Piston 12 is slidably fitted in the large diameter hole a _3, the large diameter hole a ₃ by its piston 12
The inside is partitioned into a first hydraulic chamber 13 on the side of the medium diameter hole a ₂ and a second hydraulic chamber 14 on the opposite side . The piston 12 integral with the piston rod 15 is slidably fitted in the small diameter hole a _1, the small-diameter hole a ₁ by the piston rod 15,
A gas flow chamber 16 communicating with the blow hole 9 is formed.
A rod-shaped valve body 17 having a smaller diameter than that of the piston rod 15 is integrally provided at the tip of the piston rod 15.
Be inserted and removed. Step b between the medium diameter hole a ₂ and the large diameter hole a ₃
Acts as a stopper for the piston 12, and the piston 1
When 2 abuts against the stepped portion b, the valve body 17 is inserted into the blowing hole 9 and closes it.

The first and second hydraulic chambers 13 and 14 include oil passages 18,
The first switching valve 20 is connected to the first and second ports via 19, and the pressure port of the first switching valve 20 is connected to the hydraulic pressure source 21 and the return port is connected to the oil tank 22. The flow chamber 16 is connected to a first high pressure gas supply source 25 such as nitrogen gas via a gas passage 24 having a shutoff valve 23.

Further, the movable mold 3 is provided with an outflow passage opening / closing mechanism 26 for opening / closing the outflow passage 6. The outflow passage opening / closing mechanism 26 is configured as follows.

A guide hole 2 that intersects the outflow passage 6 in the movable mold 3.
The movable die 3 is provided with a second hydraulic cylinder 28 which is formed with the guide hole 27 and which opens and closes the outflow passage 6 through the guide hole 27.
The cylinder body 29 of the second hydraulic cylinder 28 has a small diameter hole c ₁ , a medium diameter hole c ₂ and a large diameter hole c ₃ which are sequentially arranged from the guide hole 27 side toward the outside of the movable mold 3 . Large diameter hole c
_A piston 30 is slidably fitted into the third hydraulic pressure chamber 3, and the piston 30 causes the inside of the large-diameter hole c _{3 to} have the first hydraulic chamber 3 on the side of the medium-diameter hole c _2.
1 and therewith is partitioned into a second hydraulic chamber 32 on the opposite side. A rod-shaped valve element 33 integral with the piston 30 is slidably fitted in the small-diameter hole c ₁ and the guide hole 27.
3 intersects with the outflow passage 6. Medium diameter hole c ₂
The step portion d between the large diameter hole c ₃ and the large hole c ₃ functions as a stopper of the piston 30, and the valve body 33 closes the outflow passage 6 when the piston 30 collides with the step portion d.

The valve element 33 is made of a material having a low thermal conductivity, for example, a stainless material, which prevents the molten synthetic resin coming into contact with the valve element 33 from solidifying. Disc 3
A heater for heating may be built in 3.

The first hydraulic chamber 31 is connected to the oil passage 18 on the first hydraulic chamber 13 side of the gas blowing mechanism 8 via an oil passage 34. The second hydraulic chamber 32 is connected to the oil passage 19 on the side of the second hydraulic chamber 14 of the gas blowing mechanism 8 via the oil passage 35.

Gas is blown into the movable mold 3 in the overflow chamber 7, in the illustrated example, the excess resin flowing into the overflow chamber 7 when the outflow passage 6 is opened, so that the hollow molded body in the molding cavity 4 is maintained in pressure. A holding pressure applying mechanism 36 for applying the pressure is provided. The holding pressure applying mechanism 36 is configured as follows.

A gas blowing hole 37 communicating with the overflow chamber 7 is formed in the movable die 3, and a third hydraulic cylinder 38 for opening and closing the blowing hole 37 is attached to the movable die 3. The cylinder body 39 of the third hydraulic cylinder 38 has the blow hole 3
Small diameter holes e sequentially arranged from the 7 side toward the outside of the movable mold 3
₁ , having a medium diameter hole e ₂ and a large diameter hole e ₃ . Its large diameter e ₃ the piston 40 is slidably fitted, the piston 40 by the large diameter e ₃ in the first hydraulic chamber 41 of the middle diameter hole e ₂ side at the same side opposite the second hydraulic chamber 42 is divided into a.
The piston 40 integral with the piston rod 43 to the small-diameter hole e ₁ is slidably fitted, by its piston rod 43 to the small-diameter hole e _1, gas distribution chamber 44 which communicates with the blow holes 37 are formed It At the tip of the piston rod 43,
A rod-shaped valve body 45 having a smaller diameter than that is integrally provided,
The valve body 45 is inserted into and removed from the blow hole 37. Medium diameter hole e ₂
And the stepped portion f between the large diameter hole e ₃ functions as a stopper of the piston 40, and when the piston 40 abuts the stepped portion f, the valve element 45 is inserted into the blow hole 37 and closes it.

The first and second hydraulic chambers 41 and 42 include oil passages 46,
The second switching valve 48 is connected to the first and second ports of the second switching valve 48 via 47, the pressure port of the second switching valve 48 is connected to the hydraulic pressure source 21, and the return port of the second switching valve 48 is connected to the oil tank 22. . The flow chamber 44 is connected to a second high pressure gas supply source 51 such as nitrogen gas via a gas passage 50 having a shutoff valve 49. The gas injection pressure of the second high pressure gas supply source 51 is set to be higher than the gas injection pressure of the first high pressure gas supply source 25.

Next, the molding operation of the hollow molded body will be described. (A) As shown in FIG. 1, with the mold 1 closed, the first, second switching valves 20, 48 are held at the first switching position G, and the first, second, and third hydraulic cylinders 10 are held. , 28, 3
The first hydraulic chambers 13, 31, 41 of No. 8 are connected to the oil tank 22, and the second hydraulic chambers 14, 32, 42 are connected to the hydraulic power source 21, respectively, and the pistons 12, 30, 40 are operated to operate the first hydraulic chambers.
By advancing the valve body 17 of the hydraulic cylinder 10, the blowing hole 9 is closed, by advancing the valve body 33 of the second hydraulic cylinder 28, the outflow passage 6 is closed, and further advancing the valve body 45 of the third hydraulic cylinder 38. The blowing hole 37 is closed by. (B) Both the shutoff valves 23 and 49 are opened, the first and second high pressure gas supply sources 25 and 51 are operated, and the high pressure gas is supplied to both flow chambers 1.
6,44. (C) Cavity 4 through the gate 5 from the injection nozzle
Then, the molten synthetic resin R is injected and filled. In this case, the outflow passage 6 is not filled until the cavity 4 is filled with the molten synthetic resin R.
Is closed, the injection pressure sufficiently acts on the molten synthetic resin R, and the contact surface side of the molten synthetic resin R with the inner surface of the cavity 4 is smoothed. The contact surface side is cooled by the molding die 1 and becomes hard to flow, and consequently forms the skin layer of the hollow molded body.

Further, the injection pressure of the molten synthetic resin R does not also serve as a holding pressure, so that it is set to a relatively low value, which suppresses the occurrence of burrs. (D) As shown in FIG. 2, the first switching valve 20 is switched to the second switching position H so that the first hydraulic chambers 13 and 31 of the first and second hydraulic cylinders 10 and 28 serve as the hydraulic power source 21, and The two hydraulic chambers 14 and 32 are connected to the oil tank 22, respectively, and the pistons 12 and 30 are actuated to retract the valve body 17 of the first hydraulic cylinder 10 to open the blow hole 9 and to open the second hydraulic cylinder 28. The outflow passage 6 is opened by retreating the valve body 33.

At the same time, high-pressure gas is blown into the molten synthetic resin R through the blowing holes 9, whereby a cavity v ₁ is formed in the molten synthetic resin R and the excess resin r is discharged from the outflow passage 6.
Through to the overflow chamber 7 and the hollow molded body M ₁ is molded.

In the molten synthetic resin R, the excess resin r flowing out into the overflow chamber 7 is a resin existing inside because the contact surface side with the inner surface of the cavity 4 is cooled by the molding die 1 and becomes hard to flow. Therefore, the outflow does not roughen the surface of the hollow molded body M ₁ . Since high gas pressure in the hollow molded body M ₁ of the cavity v ₁ is acting equally, uniform wall thickness can be achieved. (E) As shown in FIG. 3, after the excess resin r is substantially filled in the overflow chamber 7, the second switching valve 48 is switched to the second switching position H to set the first hydraulic chamber 41 of the third hydraulic cylinder 38. The oil pressure source 21 and the second oil pressure chamber 42 are connected to the oil tank 22, respectively, and the piston 40 is operated to retract the valve body 45 to open the blowing hole 37.

At the same time, in the excess resin r, a cavity v in the illustrated example.
High-pressure gas is blown into the small cavity v ₂ communicating with ₁ through the blowing hole 37, and the volume of the small cavity v ₂ is expanded. Then, since the holding pressure is applied to the hollow molded body M ₁ as the volume of the small hollow portion v ₂ increases, sink marks in the hollow molded body M ₁ are significantly suppressed by the holding pressure.

In this way, it is possible to obtain a hollow molded article M ₁ having a good surface property and a uniform wall thickness.

4 and 5 show another embodiment of the molding apparatus, which is used for molding a solid molded body.

In FIG. 4, a molding die 52 is composed of a fixed die 53 and a movable die 54, and a molding cavity 55, a gate 56 communicating with one end of the cavity 55 and the other end of the cavity 55 by the two dies 53, 54. An overflow chamber 58 communicating with the outflow passage 57 is formed. The fixed die 53 is provided with a hot runner block 59 and an injection nozzle 60 connected to the block 59, and the injection nozzle 60 communicates with the gate 56. The movable mold 54 is provided with a knockout pin 61.

In the movable die 54, a pressure holding mechanism 36 is provided near the overflow chamber 58. Since the mechanism 36 has the same structure as that described above, the same parts are designated by the same reference numerals and the description of the structure will be omitted. However, the gas injection pressure of the second high-pressure gas supply source 51 may be lower than that in the above embodiment.

Next, the molding operation of the solid molded body will be described. (A) As shown in FIG. 4, in a state where the molding die 52 is closed, the second switching valve 48 is held at the first switching position G and the first hydraulic chamber 41 of the third hydraulic cylinder 38 is moved to the oil tank 22.
Further, the second hydraulic chamber 42 is connected to the hydraulic power source 21, respectively, and the piston 40 is operated to advance the valve body 45 of the third hydraulic cylinder 38 to close the blowing hole 37. (B) The shutoff valve 49 is opened, and the second high-pressure gas supply source 51
Is operated to introduce high-pressure gas into the flow chamber 44. (C) The injection nozzle 60 injects the molten synthetic resin R into the cavity 55 through the gate 56. The resin R is filled in the cavity 55 and a solid molded body M ₂ is molded,
The excess resin r passes through the outflow passage 57 to the overflow chamber 5
Runs out to 8.

In this case, the injection pressure of the molten synthetic resin R is set relatively low to the extent that a predetermined space is left between the excess resin r and the overflow chamber 58, which suppresses the occurrence of flash. . (D) As shown in FIG. 5, the second switching valve 48 is switched to the second switching position H to move the first hydraulic chamber 4 of the third hydraulic cylinder 38.
1 to the hydraulic source 21 and the second hydraulic chamber 42 to the oil tank 22.
To the valve element 45 by operating the piston 40.
The blow hole 37 is opened by retreating.

At the same time, in the excess resin r in the overflow chamber 58.
High-pressure gas is blown into the blowhole 37 through the
Small cavity v in excess resin r₂Is formed and its small cavities
Part v ₂With the expansion of the volume of₂Holding pressure is applied to
To be done.

By this holding pressure, sink marks in the solid molded body M ₂ are significantly suppressed, so that the surface property of the solid molded body M ₂ is improved and the wall thickness is made uniform.

FIG. 6 shows a modification of the molding die 52 of FIG.
Then, at the entrance of the outflow passage 57, a small cavity v ₂Is cavity 5
5 is provided with a protrusion 62 for preventing the extension of
It Due to the blocking action of the protruding portion 62, the solid molded body M is₂To
It is possible to reliably prevent the formation of bubbles in the air.

[0034]

According to the present invention, by providing the holding pressure imparting mechanism by blowing gas as described above, it becomes possible to set the injection pressure of the molten synthetic resin to a relatively low level, which allows the mold It is possible to provide a molding apparatus that can suppress the occurrence of flash without increasing the tightening force and has a low equipment cost.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a hollow molded body molding apparatus showing a state where a cavity is filled with a molten synthetic resin.

FIG. 2 is a vertical cross-sectional view of a hollow molding body molding apparatus showing a state in which a gas is blown into a molten synthetic resin filled in a cavity.

FIG. 3 is a vertical cross-sectional view of a hollow molded body molding apparatus showing a state in which a holding pressure is applied to the hollow molded body.

FIG. 4 is a vertical cross-sectional view of a molding apparatus for a solid molded body, showing a state in which a cavity is filled with molten synthetic resin.

FIG. 5 is a vertical cross-sectional view of a main part of a molding device for a solid molded body, showing a state where a holding pressure is applied to the solid molded body.

FIG. 6 is a vertical cross-sectional view of a main part of another solid-state molded product forming apparatus showing a state where a holding pressure is applied to the solid molded product.

[Explanation of symbols]

1,52 Mold 4,55 Cavity 5,56 Gate 7,58 Overflow chamber 8 Gas injection mechanism 36 Pressure holding mechanism M ₁ Hollow molded body M ₂ Solid molded body R Melted synthetic resin r Excess resin v ₁ Cavity part

Claims (2)

[Claims] 1. A mold (1) having a molding cavity (4), a gate (5) communicating with the molding cavity (4) and an overflow chamber (7) communicating with the molding cavity (4). A hollow molded body (M ₁ ) by forming a cavity (v ₁ ) in the molten synthetic resin (R) injected into the molding cavity (4) through the gate (5)
In order to shape the said and blow the molten synthetic resin (R) gas into the free gas blow mechanism (8), the hollow molded body (M ₁₎ in order to impart holding pressure, said overflow chamber (7) in 1. A molding apparatus for a synthetic resin molded body, comprising: a holding pressure imparting mechanism (36) for blowing gas into the chamber. 2. A mold (52) having a molding cavity (55), a gate (56) communicating with the molding cavity (55), and an overflow chamber (58) communicating with the molding cavity (55). , The gate (5
Gas is blown into the overflow chamber (58) in order to apply a holding pressure to the solid molded body (M ₂ ) made of the molten synthetic resin (R) injected into the molding cavity (55) through 6). A molding device for a synthetic resin molded body, which is provided with a pressure holding mechanism (36).