JPH0732404A - Gas recovery method in gas assist injection molding and gas assist injection molding machine therefor - Google Patents

Abstract

PURPOSE:To obtain a gas recovery method in gas assist injection molding and a gas assist injection molding machine therefor by which a high-pressure gas can be recovered without using a large-size gas recovery tank. CONSTITUTION:Using a high-pressure gas supply device provided with a first pressure increasing mechanism 20 increasing the pressure of a gas introduced to gas chambers 22C, 22D to a predetermined pressure and a second pressure increasing mechanism 30 having a compression cylinder 32 to which the high- pressure gas fed from the gas chambers 22C, 22D is itroduced and a drive cylinder 31 driving the compression cylinder 32 for boosting the high-pressure gas from the first pressure increasing mechanism 20, the high-pressure gas is injected into a melt resin 4 charged in a mold 2 to mold the melt resin 4. After that, when the gas is discharged from the inside of the melt resin 4, the gas is recovered into the drive cylinder 31 of the second pressure increasing mechanism 30 to be reused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas recovery method for gas-assisted injection molding and a gas-assisted injection molding machine therefor, which can be used for manufacturing plastic products and the like.

[0002]

BACKGROUND ART Gas-assisted injection molding has been conventionally known as an injection molding method capable of obtaining a large-sized plastic molded product having high dimensional accuracy and a thick plastic hollow body such as a heat insulating container. This gas-assisted injection molding is performed by injecting a high-pressure inert gas to inflate the molten resin filled in the mold to perform injection molding. Since a large amount of high-pressure gas is used in such gas-assisted injection molding, if all the used high-pressure gas is discarded into the atmosphere, the energy required for pressurization will be discarded, which is economical. The loss is significant. Therefore, a gas recovery tank is provided so that the used high-pressure gas can be reused in the next gas-assisted injection molding, and the used high-pressure gas is recovered therein.

[0003]

However, a large-sized gas recovery tank requires a large installation area and a high construction cost, so that there is a problem that the initial cost increases. Also, since the large gas recovery tank has an enormous volume of high-pressure gas, once the internal pressure drops, it takes a long time to recover the internal pressure, so stop the high-pressure gas supply device. There is a problem that a large amount of energy is lost when the pressure of the large gas recovery tank is lowered.

An object of the present invention is to provide a gas-assisted injection molding gas recovery method and a gas-assisted injection molding machine for the gas-assisted injection molding, which can recover high-pressure gas without using a large-sized gas recovery tank.

[0005]

A gas recovery method for gas-assisted injection molding according to the present invention comprises a first pressure increasing mechanism for increasing the pressure of a gas introduced into an air chamber to a predetermined pressure, and the air chamber of the first pressure increasing mechanism. Second pressurizing mechanism for boosting the high-pressure gas from the first pressurizing mechanism, having a small-diameter squeezing cylinder into which high-pressure gas sent from A gas recovery method for gas-assisted injection molding, wherein a high-pressure gas is injected into a molten resin filled in a mold to perform injection molding, and the gas is discharged from the inside of the molten resin. The gas is collected in the drive cylinder of the second booster mechanism.

In the above, the gas collected in the drive cylinder of the second booster mechanism is stored in the air chamber of the first booster mechanism when the drive cylinder is driven in the next gas-assisted injection molding. It is desirable to press fit and reuse.

In the drive cylinder of the second booster mechanism, the gas is introduced from the inside of the molten resin into the air chamber of the first booster mechanism, and then the second booster mechanism is provided. It is preferable to recover the gas remaining inside the molten resin when returning the driving cylinder to the original state.

The gas-assisted injection molding machine of the present invention comprises a first pressure increasing mechanism for increasing the pressure of the gas introduced into the air chamber to a predetermined pressure, and a high pressure gas sent from the air chamber of the first pressure increasing mechanism. High-pressure gas supply device having a small-diameter squeezing cylinder to be introduced and a second squeezing mechanism for boosting high-pressure gas from the first squeezing mechanism having a large-diameter driving cylinder for driving the squeezing cylinder A gas-assisted injection molding machine for molding a molten resin by injecting a high-pressure gas into the molten resin filled in the mold by driving the inside of the mold and the second booster mechanism. The inside of the cylinder and the inside of the air chamber of the first pressurizing mechanism are connected to each other via a direction control valve. Here, a solenoid valve, a check valve, or the like can be adopted as the directional control valve.

[0009]

In the present invention as described above, the high-pressure gas can be collected in the drive cylinder of the second booster mechanism every time the gas-assisted injection molding is performed, and thus the large-sized gas recovery tank becomes unnecessary. This eliminates the need for large installation locations and expensive construction costs for providing a large gas recovery tank, and because the high-pressure gas capacity of the high-pressure gas supply device is small, the internal pressure will remain even if the device is stopped. Recovers in a short time and the energy lost is very small, which achieves the above-mentioned object.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of an injection molding machine 1 of this embodiment. The injection molding machine 1 fills a molten resin 4 from a nozzle 3 set in a mold 2 and at the same time A high-pressure inert gas supplied from a high-pressure gas supply device 5 is pressed into the interior of the nozzle 3 to form a hollow product. The high-pressure gas supply device 5 squeezes the nitrogen gas, which is an inert gas taken out of the cylinder 10, by the first pressure increasing mechanism 20 and the second pressure increasing mechanism 30 and then melts the molten resin 4
It is to be pumped in.

The first booster mechanism 20 has two cylinder devices, a drive cylinder 21 and a compression cylinder 22, and
The piston rod 21A of the drive cylinder 21 and the piston rod 22A of the compression cylinder 22 are interconnected. The drive cylinder 21 is a so-called double-acting air cylinder whose diameter is larger than that of the compression cylinder 22. Both sides of the piston 21B of the drive cylinder 21 are air chambers 21C and 21D into which compressed air is introduced. These two air chambers 21C and 21D are connected via a switching solenoid valve 11 to a compressed air source (not shown). By the operation of the switching solenoid valve 11,
Compressed air is alternately introduced into the air chambers 21C and 21D, and the compressed air causes the piston 21B to reciprocate to move the piston rod.
The squeeze cylinder 22 is driven via 21A.

The compression cylinder 22 has two air chambers 22C and 22D for introducing nitrogen gas on both sides of the piston 22B. The two air chambers 22C and 22D are connected to the cylinder via the check valve 12.
10 and the second booster mechanism 30. piston
22B reciprocates due to the operation of the drive cylinder 21, and
2nd by compressing the nitrogen gas introduced into 22C and 22D alternately
It is designed to be sent to the booster mechanism 30 of.

The second booster mechanism 30 has the same structure as the first booster mechanism 20, and has a drive cylinder 31 and a squeeze cylinder 32 in which respective piston rods 31A and 32A are connected to each other. . The drive cylinder 31 is a double-acting air cylinder device having a larger diameter than the squeeze cylinder 32, and has two air chambers 31C and 31D on both sides of the piston 31B. Of these, the lower air chamber 31C in the figure is the switching solenoid valve.
It is connected via 13 to a compressed air source (not shown). When the switching solenoid valve 13 is operated, compressed air is introduced into the air chamber 31C, and the compressed air causes the piston 31B to move forward and the piston 32B of the compression cylinder 32 to move forward via the piston rod 31A. On the other hand, piston rod 31A
The air chamber 31D on the side is connected to the nozzle 3 via the check valve 14, the filter 15, and the solenoid valve 16, and the check valve 17
Through the air chamber 22 of the compression cylinder 22 on the side of the first lifting mechanism 20
It is connected to C and 22D. When the switching solenoid valve 13 is turned off to open the air chamber 31C to the atmosphere and the solenoid valve 16 is operated to communicate the air chamber 31D with the inside of the molten resin 4, the inside of the molten resin 4 is High-pressure nitrogen gas from the piston 31B was recovered in the air chamber 31D and moved forward by the pressure of the high-pressure nitrogen gas.
Is set back to its original position.

The compression cylinder 32 is a pressure booster for maintaining a predetermined pressure so that the pressure does not drop when the nitrogen gas compressed by the compression cylinder 22 of the first pressurizing mechanism 20 is sent into the molten resin 4. Piston 32 of squeeze cylinder 32
Only the upper side of B in the figure is the air chamber 32C.
Is connected to the first booster mechanism 20, and the solenoid valve 18
It is connected to the nozzle 3 via. First boost mechanism 20
The nitrogen gas compressed by the first pressurizing mechanism 20 is sent to the inside of the molten resin 4 by driving the piston 32B of the compression cylinder 32 forward with the drive cylinder 31 while introducing the nitrogen gas from the gas chamber 32C into the air chamber 32C. At the same time, the nitrogen gas is maintained at a predetermined pressure.

Next, the operation of this embodiment will be described. First,
As shown in FIG. 2A, the drive cylinder 21 of the first booster mechanism 20 is actuated to move the cylinder 10 to the compression cylinder 22.
The pressure of the nitrogen gas introduced into the second pressurizing mechanism 30 is increased and sent to the pressing cylinder 32 of the second pressurizing mechanism 30. The operation of the drive cylinder 21 is continued until the nitrogen gas in the compression cylinder 32 reaches a predetermined pressure, and the nitrogen gas is stored in the compression cylinder 32 while increasing the pressure. On the other hand, the molten resin 4 is filled in the mold 2. At this time, the air chamber of the drive cylinder 31 of the second booster mechanism 30.
The nitrogen gas collected from the inside of the molten resin 4 in the previous injection molding is accumulated in 31D. In addition, this air chamber
The gas recovered in 31D has a pressure (hereinafter referred to as "secondary recovery pressure") that is considerably lower than a predetermined pressure when the gas is injected into the molten resin 4 for the reason described later.

Next, when the nitrogen gas in the compression cylinder 32 reaches a predetermined pressure, the drive cylinder of the first booster mechanism 20.
21 is stopped and the drive cylinder 31 of the second booster mechanism 30 is operated. As a result, as shown in FIG. 2B, the high-pressure nitrogen gas in the compression cylinder 32 is pressed into the molten resin 4 in the mold 2, and the nitrogen gas recovered in the air chamber 31D is first It is transferred to the inside of the squeezing cylinder 22 of the pressure increasing mechanism 20.

Next, when the surface of the molten resin 4 is cured to such an extent that it does not lose its shape, the high-pressure nitrogen gas inside the molten resin 4 is fed to the first pressurizing mechanism 20 as shown in FIG. 2C. It is sent to the inside of the compression cylinder 22 and collected. Since the high-pressure nitrogen gas recovered here has a high pressure (hereinafter referred to as “first recovery pressure”) close to a predetermined pressure when it is pressed into the molten resin 4, it is previously stored in the compression cylinder 22. Second
Even if nitrogen gas at the next recovery pressure is accumulated, it can be recovered inside the compression cylinder 22. At this time, the nitrogen gas at the primary recovery pressure also flows into the air chamber 31D of the drive cylinder 31 of the second booster mechanism 30, but the piston 31B is urged by the compressed air supplied to the air chamber 31C on the opposite side. As a result, the air chamber 31D is maintained in a compressed state, so that a small amount of nitrogen gas can be collected in the air chamber 31D.

Next, when the pressure in the molten resin 4 equilibrates with the pressure in the compression cylinder 22 and nitrogen gas cannot be collected in the compression cylinder 22, the compressed air source in the air chamber 31C is opened to the atmosphere, As shown in FIG. 2D, the pressure of the nitrogen gas in the molten resin 4 causes the piston 31B of the drive cylinder 31C to retreat to expand the volume of the air chamber 31D, while remaining in the molten resin 4. The existing nitrogen gas is collected inside the air chamber 31D. Since the residual nitrogen gas that cannot be recovered by the compression cylinder 22 is the gas recovered inside the air chamber 31D, as described above, when the gas is injected into the molten resin 4 during injection molding. Second much lower than the prescribed pressure of
It is the next recovery pressure. Nitrogen gas consumed by gas-assisted injection molding is performed by recovering nitrogen gas while maintaining high pressure by the above procedure and reusing nitrogen gas pressurized to high pressure many times. And save energy required to pressurize the gas.

According to this embodiment as described above, the following effects can be obtained. That is, after the gas-assisted injection molding is performed each time, the used nitrogen gas is accumulated inside the compression cylinder 22 of the first booster mechanism 20 and the drive cylinder 31 of the second booster mechanism 30. Nitrogen gas that maintains high pressure can be recovered and reused without a large gas recovery tank.

Therefore, the injection molding machine 1 does not require a large installation area and a large construction cost for providing a large-sized gas recovery tank, so that the initial cost for installation can be reduced and the high-pressure gas supply device 5 can be installed. Even if the holding capacity of the high-pressure gas becomes small and the apparatus is stopped and the internal pressure drops, the pressure is recovered in a short time, so the energy lost when the high-pressure gas supply apparatus 5 is started is extremely reduced. The size can be reduced, and the running cost of the injection molding machine 1 can be reduced.

In recovering the high-pressure nitrogen gas in the molten resin 4, first, the first pressure increasing mechanism 20 is operated at the primary recovery pressure.
Since it is collected in the squeezing cylinder 22 and the rest is collected in the drive cylinder 32 of the second booster mechanism 30 at the second collecting pressure, the nitrogen gas pressed into the molten resin 4 can be collected with almost no leakage. it can. At this time, the nitrogen gas recovered at the secondary recovery pressure is removed from the drive cylinder 31 of the second booster mechanism 30 before the nitrogen gas recovered at the primary recovery pressure during the next injection molding is injected. Since it is transferred to the compression cylinder 22 of the first pressurization mechanism 20, the nitrogen gas at the secondary recovery pressure can be effectively reused without lowering the primary recovery pressure.

Further, the second boosting mechanism is operated at the secondary recovery pressure.
Since the piston 32B of the drive cylinder 31 is returned to the original position by the nitrogen gas of the secondary recovery pressure when recovering the drive cylinder 31 of 30, the drive energy of the drive cylinder 31 can be saved.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes can be made without departing from the gist of the present invention. It is possible. For example, in the above-described embodiment, the used nitrogen gas is collected in both the compression cylinder 22 of the first pressure increasing mechanism 20 and the drive cylinder 31 of the second pressure increasing mechanism 30, but the second pressure increasing mechanism 30 having a large volume is used. May be recovered only in the drive cylinder 31 of the first pressurizing mechanism 20. In this case, when the nitrogen gas is reused in the next injection molding, the power of the compressed air source or the like is used to remove the nitrogen gas from the first pressurizing mechanism 20. It may be transferred to the compression cylinder 22.

The inert gas is not limited to nitrogen gas, but may be other inert gas such as argon gas. further,
The first boosting mechanism is not limited to the pneumatically driven type that is driven by compressed air, but may be a hydraulically driven type.

[0025]

As described above, according to the present invention, it is possible to recover the high-pressure gas used in the gas assist injection molding without using a large gas recovery tank.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the embodiment.

[Explanation of symbols]

 1 Gas-assisted injection molding machine 2 Mold 4 Molten resin 5 High-pressure gas supply device 12, 14, 17 Check valve as a directional control valve 16 Solenoid valve as a directional control valve 20 First booster mechanism 22C, 22D Air chamber 30 Second boost mechanism 31 Drive cylinder 32 Squeeze cylinder

Claims (4)

[Claims] 1. A first pressurizing mechanism for pressurizing a gas introduced into an air chamber to a predetermined pressure, and a small-diameter squeezing cylinder into which high-pressure gas sent from the air chamber of the first pressurizing mechanism is introduced. And a second pressurizing mechanism for boosting the high-pressure gas from the first pressurizing mechanism having a large-diameter drive cylinder for driving the pressurizing cylinder, and a high pressure inside the molten resin filled in the mold. Is a gas recovery method for gas-assisted injection molding in which the gas is injected under pressure, and the gas is collected in the drive cylinder of the second booster mechanism when the gas is discharged from the inside of the molten resin. A gas recovery method for gas-assisted injection molding, comprising: 2. The gas recovery method for gas-assisted injection molding according to claim 1, wherein the gas recovered in the drive cylinder of the second booster mechanism is used for the next gas-assisted injection molding. A gas recovery method for gas-assisted injection molding, comprising press-fitting into the air chamber of the first pressure-increasing mechanism for reuse when driven. 3. The gas recovery method for gas-assisted injection molding according to claim 1, wherein after introducing the gas from the inside of the molten resin into the air chamber of the first pressurizing mechanism, Gas assist injection, characterized in that when the drive cylinder of the second booster mechanism is returned to its original state, the gas remaining inside the molten resin is recovered inside the drive cylinder of the second booster mechanism. Gas recovery method for molding. 4. A first pressure increasing mechanism for increasing the pressure of the gas introduced into the air chamber to a predetermined pressure, and a small-diameter squeezing cylinder into which the high-pressure gas sent from the air chamber of the first pressure increasing mechanism is introduced. And a second pressurizing mechanism for boosting the high-pressure gas from the first pressurizing mechanism, which has a large-diameter drive cylinder for driving the compressing cylinder, and is melted in a mold by a high-pressure gas supply device. A gas-assisted injection molding machine for molding a molten resin by injecting a high-pressure gas into a resin, the inside of the mold, the inside of a drive cylinder of the second booster mechanism, and the first The gas-assisted injection molding machine characterized in that the inside of the air chamber of the booster mechanism is connected to each other via a direction control valve.