JPH02223421A - Injection molding machine and its operation method - Google Patents

Abstract

PURPOSE: To exclude cold slugs existing in a case where gas is to be exhausted in a state the gas is injected at a nozzle part, by providing a gas injecting means with a gas inlet opened to a sprue passage so as to inject the gas into a molten plastic which passes through the sprue passage. CONSTITUTION: A shut-off valve 76 of a nozzle is opened under control of an injection cycle controller for an injection molding apparatus 22 and a screw 74 is actuated in such a way that a molten plastic 110 is injected into a mold cavity 14 through a nozzle 42, an adapter 24 and a sprue bushing 26. When the molten plastic is entered into the sprue bushing 26 through a probe 60 for gas injection, a valve 86 is immediately opened by means of a cycle controller and high pressure gas flows to a gas inlet passage 64 and a gas passage 62 through a high pressure line 65 from a chamber 82 and is injected into a stream of the molten resin in a sprue passage 38.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus and method for making injection molded thermoplastic parts, particularly gas-assisted parts having a smooth outer skin and a hollow core. Regarding injection molding.

[Conventional technology]

To date, various efforts have been made to achieve weight and cost reductions using less material, while maintaining structural properties and creating a smooth outer surface or skin that does not require sanding or other finishing. injection molding techniques have been proposed. Using foaming agents including gas,
Porous, cellular, or cellular cores can be produced, and in some cases hollow cores can also be produced. When a gas is used to form the hollow core, it directs the flow of the molten plastic from a nozzle or directly into the mold, preferably in a controlled manner to obtain the desired core structure. Can be injected into the inside.

Hendry, US Pat. No. 4,474,717, discloses several apparatus and methods for injecting gas into a mold with a gas injection probe.

A small amount of plastic is first injected into the mold to enclose the gas injection probe, through which gas is then injected while plastic injection continues to form the desired core structure. At the end of the molding operation, the gas pressure in the mold is relieved by evacuating the mold cavity through the probe, which acts as a pressure reducing valve.

A similar in-mold gas injection and pressure reduction valve is also disclosed in Thayer U.S. Pat. No. 4,740,150. Gas injection probes or nozzles are shown in both the Hendry and Thayer patents as being mounted on the mold half opposite the mold half into which the plastic is injected, such as from a reciprocating screw injection molding machine. ing.

Although injecting and/or venting gas into the mold cavity as taught by Hendry and Thayer may be sufficient to provide the desired core structure, the gas injection nozzle or It is necessary to modify each mold to accommodate the probe. This is especially costly when there are many mold cavities or when retrofitting an existing mold.
Also, care must be taken in selecting the position of the gas injection nozzle.

Introducing a gas or blowing agent into the molten plastic stream from the nozzle portion of a plastic injection molding machine prior to the mold cavity, as shown in Friedrich U.S. Pat. No. 4,101,617; Other gas injection techniques have also been proposed, such as introducing gas or blowing agent into the cavity after injection of the plastic by a special manifold as shown in Olabisi U.S. Pat. No. 4,136,220. ing. However, even in these cases, modifying the nozzle or manifold is still costly and requires changing the nozzle or manifold for different applications depending on the part being molded by the molding machine.

Other gas injection locations have also been proposed. Gahan, U.S. Pat. No. 4,498,860, discloses a telescoping angled piston in a mold half that can be extended to close off a reversely tapered sprue passage; This blocks the sprue. A small vibrator concentric with the piston is disclosed for injecting gas into the plastic material so that the gas flows with the plastic through the mold area. However, in this case as well, relatively precise modification of the mold is required to accommodate the holder for the sprue opening/closing piston. The slanted orientation of the gas injection tube causes uneven distribution of gas in the plastic entering the mold.
Alternatively, it is certain that effective gas injection will be impaired.

Injection of gas, whether the gas is injected into the mold, as in the Thayer and Hendry patent, or into the molten resin stream before the mold, as in the Friedrich patent. In order to accurately control the gas injection, the injection of these gases must be compatible with various gas injection systems. This may require further modification of the nozzle or mold, especially if a previously solid part is being made into a part with a hollow core and the gas injection system is subsequently installed into an existing mold. This increases costs in some cases.

Similarly for new equipment, but also for retrofitting into existing injection molding machines and molds, to more precisely control gas injection to repeatedly obtain the desired core structure over long production runs. Various techniques have been proposed. One attempt is described in general terms in the aforementioned U.S. Pat. No. 4,740,150 to Thayer, and in British patent specification no. , a predetermined or metered volume of compressed gas is injected into the mold during each molding cycle.

Also - a method of using what has already been described under the term preset pressure in boat fishing was filed on May 5, 1987,
Published in Publication No. 87152 on December 12, 987 No. 02
It is proposed in Bakshi European Patent Application No. 87304002.6 published as 50080A2.

According to this method, in contrast to techniques using predetermined volumes, the amount of gas introduced into the mold is not directly metered, but only the pressure of the gas is controlled. A gas supply is provided along with a gas compression device to compress the gas to a preset pressure, which preset pressure is at least as great as the pressure at which the molten plastic material is introduced into the mold. A storage chamber is provided for storing gas at a preset pressure so that the gas is immediately available when injection of the plastic material is started. Upon cooling of the plastic, the gas pressure holds the plastic against the inner surface of the mold cavity until the plastic is able to maintain the shape dictated by the mold to yield an essentially hollow part. As described in European Patent Publication No. 0.250.080, prior to injection of the plastic, a high pressure gas storage tank is completely filled with a preset pressure for the molding operation. Immediately after plastic injection begins, high pressure gas from a storage tank is injected into the molten plastic stream by a feed chamber in the nozzle. The high pressure tank is filled and refilled by a pump controlled by a pressure switch, thus ensuring that sufficient gas at a preset pressure is always available in the high pressure tank. October 25, 1973
The application was filed on March 27, 1982, and the patent application was filed on March 27, 1982.
Asahi Dow Co., Ltd.’s patent application published as No. 968 in 1972
No. 120318 shows a similar arrangement for injecting gas through an inlet in a high pressure piston or ram and nozzle.

[Problem to be solved by the invention]

Although the predetermined or preset volume and preset pressure methods described in the prior art can give sufficiently good results, in contrast to the injection of gas that is not precisely controlled, Both methods have the disadvantage of not providing accurate and reproducible control of gas injection. That is, constant volume methods remain reproducible over many molding cycles due to the inherent changes in the constant volume cylinder and piston configuration due to long-term use and wear and other variations over time. That is difficult. Also, in the preset pressure method, the high pressure pressure storage tank used must be filled and the preset pressure can change during the injection cycle as gas is released from the tank and refilled by the pump. .

It would therefore be desirable to provide an improved method and apparatus for injection molding hollow parts that overcomes the aforementioned problems and other difficulties while providing better and more advantageous overall results.

[Means to solve the problem]

In accordance with the present invention, a new and improved method and apparatus for manufacturing hollow injection molded parts is provided.

More particularly, according to one important aspect of the invention, a method and apparatus for making plastic injection molded parts having a smooth surface or skin are provided, in which a thermoplastic material is deposited as a molten stream. , is injected into the mold cavity through a sprue bushing fixed to the mold. At the same time, an unmetered amount of inert gas is passed through the thermoplastic material substantially concentrically with the melt flow and at a pressure sufficient to form a gas cavity in the melted material within the mold. It is then introduced into the molten stream through the adapter at the sprue bushing. Adapters can also be added to existing sprue bushings for retrofitting into existing molds. For new molds, the sprue bushing will be modified on the nozzle side.

According to another aspect of the invention, during injection of the plastic:
Plastics are self-supporting
The gas is maintained at a predetermined, constant, and appropriately high pressure to hold the plastic against the mold surface until .ng). This gas returns through the sprue bushing and adapter and is exhausted from the mold before the mold is opened. By means of a large cylinder with a volume displacement element inside, controlled by a pressure sensor in the gas pressure line up to the mold, a preset, suitably high pressure is maintained in the gas supply within the cavity during injection and cooling. A suitable preset gas pressure at is maintained.

The basic aim of the invention is to overcome, or at least minimize, the disadvantages of gas-assisted injection molding in the prior art;
A method and apparatus for gas-assisted injection molding for producing superior plastic parts having hollow internal cavities, smooth outer surfaces, and less burrs and shavings. The object of the present invention is to provide a method that is efficient, economical, and provides great flexibility in using conventional injection molding machines.

〔Example〕

The above objects and other features and advantages of the invention will become apparent from the following detailed description, claims, and accompanying drawings.

It should be understood that the accompanying drawings merely illustrate preferred embodiments of the invention, and that other embodiments are within the scope of the claims.

Referring generally to the molding machine shown in FIG. 1, the stationary mold half 10 and the movable mold half 12 are shown in their closed positions, with the outer shell 18 and hollow core 2
A mold cavity 14 is defined for molding a plastic part 16 having a diameter of 0.0. Plastic is injected into the cavity 14 through the sprue bushing adapter 24 and the sprue bushing 26. Gas from a supply device, generally indicated at 28, enters the flow of molten resin.
It is introduced in sprue passage 38 via adapter 24 . In the embodiment described herein, the adapter 24
is retrofitted to an existing mold that already has a sprue bushing 26. Retrofitting is done to existing molds when it is desired to convert the molding of a solid part to the molding of the same part with a hollow core, such as core 20.

1-3, the sprue bushing 26 has a flanged head 30 which is secured to the recess 32 by a retaining plate 34 press-fitted and bolted to the mold half 10. It is set in. Sprue bushing sleeve 3 integrated with head 30
6 extends through the mold half 10 and has a sprue passage 38 which flares outwardly to open into the cavity 14 on the left side as viewed in FIG.

The sleeve 36 is also press fit into the mold half 10.

The narrow end of the sprue passage 38 opens into the head 30 in a hemispherical recess 40, which provided a seat for the nozzle 42 of the injection molding machine prior to subsequent installation of the adapter. It is something. Upon completion of injection, sprue passage 38 contains sprue in the area generally designated 41, and this sprue has gas channel 43 therethrough.

As is generally known, bushings such as sprue bushing 26 are an inexpensive means of protection for molds. That is, damage occurs to the bushing part, and the bushing can be replaced at little cost. To this end, the sprue bushing 26 typically resists the impact of the nozzle as injection pressure is applied to the sprue bushing 26 and nozzle 42 interface, both during deployment and during repeated injection cycles. Manufactured from hardened steel.

The sprue passages 38 are typically polished and have a highly polished finish to minimize friction with the molten plastic, thereby minimizing frictional heating of the plastic that could cause deterioration or burns in the final product. Repeated injection through the sprue passageway 38 over an extended period of time can cause surface scratches and scorches due to the abrasive nature of the plastic material. This wear and surface imperfection is caused by glass-filled plastics, for example. Worn sprue passages also create turbulence and frictional flow on the walls, especially during high-speed injection cycles, creating undesirable pressure drops that prevent proper filling of the mold and prevent plastic from filling every nook and cranny of the mold. impairs the flow of In any case, conventional sprue bushings provide an inexpensive way to repair damage by replacing the bushing. Although sprue bushing 26 is illustrated as being unheated, it should be understood that the present invention applies equally to applications with heated sprue bushings.

The sprue bushing adapter 24 consists of a steel body 50 having an integral torpedo-shaped web 52 that extends across a through passage 54 in the body 50.
4 into two openings 56 in a torpedo-shaped web. The main body 50 is also made of hardened steel, and the through passage 5
4 has a nozzle seat 51 on the inlet side. The main body 50 is bolted to the sprue bushing 26 at a point 58, and silver soldered to remove burrs at the interface between the head 30 and the recess 40.

Web 52 has an integral, needle-like gas injection nozzle or probe 60 extending concentrically within sprue passageway 38 and having a gas passageway 62 therein.

Adapter 24 has opposed radial gas inlet and exhaust passages 64,66 which are connected to web 52.
a probe 60 of the nozzle extending through and at an inner end portion of the nozzle;
It is connected in a T-shape and communicates with the gas passage 62 inside. The outer end portion of the gas inlet passage 64 is connected to the gas supply device 28 via a high pressure line 65. Gas exhaust passage 6
6 is connected to a vacuum baffle 68 via a solenoid operated valve 70 and line 72. Preferably, the gas outlet passage 66 has a diameter that is, for example, twice as large as that of the gas inlet passage 64, so that it will not become obstructed if the plastic is sucked back in when the cavity 14 is depressurized. Probe 60 is shown as extending slightly into sprue passage 38, but it can be made longer or shorter depending on the particular application. In one application, the probe opens in general alignment with the junction of recess 32 and sprue passageway 38, and in another application, the probe extends into the vicinity of cavity 14. However, in either case, the gas passage 62 is concentric with the sprue bushing and injects gas concentrically into the molten resin stream in the direction of flow of the molten material.

The injection molding machine 22 has a conventional reciprocating screw 74 and a cylinder operated shutoff valve 76.

In FIG. 1, the screw 74 is the plastic part 1.
6 is shown at the end of its stroke just before closing the isolation valve 76 so that it is substantially fully formed.

During the injection stroke, compressed gas is supplied from high pressure chamber 82 through check valve assembly 84 and valve 86 actuated by solenoid 88 to sprue bushing adapter 24 via high pressure line 65. Gas pressure within chamber 82 is monitored by gas pressure indicator sensor 90, which provides an electrical output signal to controller 92 via lead 94 when the gas pressure falls below a preset pressure. When gas in chamber 82 is supplied to high pressure line 65 through check valve assembly 84 and valve 86, piston rod 96 is connected to controller 92.
The chamber is moved by a hydraulic cylinder 98 which is actuated to reduce the volume of the chamber and keep the pressure constant.

Piston rod 96 projects into chamber 82 but has no sliding seals on chamber wall 99.

Piston rod 96 extends downwardly through hydraulic cylinder 98 and the walls of chamber 82 and through a wet metal seal 100 for piston 102 within hydraulic cylinder 98 . Low pressure gas flows from the supply tank 104 to the pressure reducing valve 10.
6 and check valve assembly 84 to chamber 82 . This gas is preferably nitrogen.

Prior to the start of the molding cycle, the solenoid operated valve 70
and 86 are closed, and inert gas is stored in chamber 82 by actuating controller 92 and hydraulic cylinder 98 to retract piston rod 96 and push piston 102 down, as seen in FIG. Ru. This draws relatively low pressure gas from supply tank 104 into empty chamber 82 . The gas is supplied to the supply tank 10 where the pressure within the chamber 82 is set by the pressure reducing valve 106 and indicated by the pressure gauge 108.
4 into the chamber 82 until the pressure equals the pressure of the gas entering from 4. The gas pressure within the chamber 82 ranges, for example, from 150 psi (1030 kPa) to 250 psi (1030 kPa).
psi (1720kPa), which is relatively low. Check valve assembly 84 prevents gas from returning to supply tank 104. Hydraulic cylinder 98 is then actuated to extend piston rod 96 into chamber 82 to the desired high pressure precented, for example, 2000 ps i (13790 kPa) or higher, as set and indicated by pressure indicator sensor 90. compress the gas.

Generally, the gas pressure is set to be at least greater than the plastic injection pressure at the sprue bushing 26 and cavity 14.

At the desired desired pressure, piston 102 stops in response to a control signal from lead 94 and remains in this raised position during subsequent injection operations until such time as the pressure falls below the desired preset gas pressure. Stay in. Chamber 8
2 is completely filled to the desired preset pressure, and with solenoid actuated valve 70, check valve assembly 84, and valve 86 closed, the molding cycle is in the starting position.

To begin the molding cycle, a mold clamping unit (not shown) is closed and the mold halves 10 and 12 are placed under a clamping force that exceeds the plastic melt injection pressure and the gas injection pressure. Keep it closed. Under the control of an injection cycle controller (not shown) for the injection molding machine 22, the nozzle shield well 76 is opened and the nozzle 42, adapter 2
4. Screw 74 is actuated to force molten plastic 110 through sprue bushing 26 and into mold cavity 14. Once the molten plastic passes through the gas injection probe 60 and into the sprue bushing 26 , the cycle controller immediately opens the valve 86 and directs the high pressure gas from the chamber 82 through the high pressure line 65 and into the gas inlet passageway 64 . and into gas passageway 62 to allow injection into the flow of molten resin within sprue passageway 38 . The gas injection is carried out in a manner similar to that disclosed in the aforementioned Hendry U.S. Pat. It is preferable to start as soon as possible. During plastic injection, the evacuation solenoid operated valve 70 remains closed.

Once the gas enters the flow of molten resin in the sprue passageway 38,
The higher pressure of this gas quickly forces the molten plastic toward the mold cavity 14 and against the cavity walls, forming a hollow core 20 as the plastic cools.

During plastic injection, it enters the flow of molten resin,
Also, the pressure of the gas held within the core 20 via the gas channels 43 during cooling is constant and does not vary significantly during the molding cycle. When the gas pressure within chamber 82 begins to drop, pressure indicator sensor 90
energizes controller 92 to move piston 102 upwardly and extend piston rod 96 further into chamber 82 to maintain gas pressure within chamber 82 and core 20 at a predetermined level.

When the screw 74 completes its forward travel, the gas flow continues for a short period of time to force the molten plastic against the mold surface. Valve 86 is then closed by the cycle controller. Controller cycle (
This gas pressure is held constant for a period of time set by the mold cavity 14 (not shown) until the molten plastic shell 18 within the mold cavity 14 has cooled sufficiently to become self-supporting. After this, a solenoid operated valve 70 for gas evacuation is opened by the cycle controller to direct gas from the cavity 14 into the sprue 41 through the open gas channel 43.
through the passageway 54 and the gas discharge passageway 66.
, line 72 and vent the exhaust gas to the atmosphere via vacuum baffle 68. The mold can then be opened and the molded plastic part 16 removed from the mold.

During the vacuum time in the cavity 4 during the molding cycle, the hydraulic cylinder 98 retracts the piston 102 and piston rod 96. Chamber 82 is refilled and piston rod 96 is then extended until the gas pressure within chamber 82 reaches the desired setting on the indicator of gas pressure indicator sensor 90 . The device is now ready to repeat the cycle with valve 86 and solenoid operated valve 70 closed.

〔Effect of the invention〕

In the above-described configuration, the gas injection probe 60 is connected to the sprue bushing 26 in the same direction as the flow of the molten resin.
It opens therein concentrically with the sprue passage 38. This allows the use of standard sprue bushings opening into the mold without changing the standard sprue bushing or opening design. This is especially important for later installations. This is because in that case, it is not necessary to change the shape of the sprue bushing, including where in the cavity the sprue passage 3B opens.

Thus, the plastic flow parameters in a standard sprue design are not varied.

Another advantage of injecting gas at the sprue bushing is that it eliminates the cold slag that is present when gas is injected and evacuated at the nozzle section. This is because as the gas exits through the nozzle, the tip of the nozzle is slightly cooled by the gas, resulting in assimilation and cold slug.

Considering a further advantage of concentric gas injection at the sprue bushing in the direction of material flow, if the plastic and gas inflow continues after the gas population has been enveloped by the flow of molten resin, an enclosure is formed. , which moves into the mold cavity 14 and expands throughout the cavity, while the enclosure is sufficiently fluid to expand under the pressure of the gas. Once the enclosure has filled the cavity to form the shell 18, the shell is held against the wall until it becomes self-supporting, especially with the pressure within this shell being kept constant. I get angry. Concentric injection of gas into the flow of molten resin at the sprue bushing provides a uniform distribution of gas and gas pressure in the envelope for the flow of molten resin and expansion in the mold cavity. Concentric injection of gas in the sprue bushing also ensures that gas enters the resin at points where the flow of molten resin is always viscous. Concentric gas injection at the sprue bushing in the direction of molten resin flow also minimizes turbulence in the molten resin flow that would result in closed cells in the final product.

Although the injection of gas in the sprue bushing has been described above in a preferred embodiment in conjunction with a constant pressure gas supply system 28, its advantages also apply to other gas supply systems of the type disclosed in the prior art mentioned above. It is useful.

Similarly, although gas injection in sprue bushings has been described so far for retrofitting into existing molds, it is equally advantageous for new molds. For new mold applications, inexpensive standard sprue bushings can be used. The adapter 24 is secured to the sprue bushing and is preferably silver brazed at the interface to prevent flash. If a special sprue bushing is required, part of the adapter can be manufactured as an integral part with the bushing. However, whether retrofitted to an existing mold or applied to a new mold, the gas injection mechanism is part of the sprue bushing and may be present in the nozzle or attached to the mold. This is in contrast to the direct case. Thus, there is no need for major modifications to either the mold or the injection molding machine. If the sprue bushing or adapter becomes worn or damaged, it can be easily removed and replaced.

Although sprue bushings are preferred for many applications, it will be appreciated that for some applications it is not necessary to include a sprue bushing in the mold. In that case, a gas injection adapter 24 is provided on the mold to carry the flow of molten resin into the cavity, so that the gas and the flow of molten resin enter the mold cavity together.

In such applications, because of the sprue, the part being molded may be non-functional at the point where the plastic is injected, or may be part of the runner, or some other part that is later removed from the final product. It has several parts. In its broadest sense, the invention therefore contemplates the use of an adapter for injecting gas into the flow of molten resin downstream of a sprue or sprue-like section of a component or a runner of a component, independently of the nozzle. .

[Other embodiments and effects]

FIG. 4 shows another embodiment of the invention in which a mold cavity (not shown) has four hot drop sprues 120, commonly known as hot drops.

Each hot drop sprue 120 has a hot runner.
122 and 123, the main sprue bushing 124 typically receives the plastic from the nozzle of an injection molding machine.
connected to. By providing an adapter, such as adapter 24, to sprue bushing 124, gas can be introduced into the melt stream for distribution to each of the four hot drop sprues 120. To further ensure an even distribution of gas to each of the hot tube sprues, the probe for injecting the gas is branched and extends through a hot runner 123. can be configured to enter each of the hot drop sprues as shown in FIG. These tubes 126
are open into the molten resin flow concentrically in each hot drop sprue 120 and in the direction of molten resin flow into the mold.

Gas supply device 28 also has advantages over the prior art supply devices described above. The gas supply 28 maintains a constant pressure during injection and cooling in the mold, ensuring that the plastic part to be molded is in full contact with the mold walls until the part is self-supporting. make sure that. As soon as any gas is released from the chamber 82, the piston rod 96 is instantaneously and automatically extended into the chamber 82 to replace the released gas and maintain a constant pressure. will be realized.

This is in contrast to the verbal system. In such systems, the pressure of the gas drops during injection, whereas prior art techniques attempted to achieve a substantially constant pressure by means of pistons, pumps, and the like.

Chamber 82, piston rod 96 and piston 10
Strokes of 2 are chosen so that the chamber 82 contains more than enough gas for each injection and the piston rod 96 never abuts the walls of the chamber. As a result, once the chamber 82 is compressed to the desired preset pressure, this pressure can be maintained throughout the injection by replacing the gas with use. This also contrasts with using a piston in a gas compression cylinder. This is because more compressed gas is stored in chamber 82 than is sufficient for each injection. Piston rod 96 does not require a piston ring or other dry sliding seal within chamber 82. Introducing lubricants into the gas can impair the surface finish of the plastic parts being molded or create undesirable surfaces or bubbles. Seal 1
00 is wetted by hydraulic fluid within the hydraulic cylinder 9, the design of such metal seals to prevent leakage of hydraulic fluid into the chamber 82 is well known. Because no extra heat is generated within chamber 82 by the friction of the moving seals, longer life and more reliable operation are achieved.

As previously mentioned, gas supply 28 is a high pressure system. The preset pressure will vary depending on the molding parameters for each application, but is typically 2000
from 7000ps + (from 13790k to 48270
(kPa) and even higher gas pressures are contemplated, the gas injection pressure being selected to be equal to or higher than the pressure of the molten resin at the point where the gas is injected. Typically, commodity polymers such as polypropylene and polyethylene are at the lower end of this range, with sprue bushings of 2
For example, 1800 psi (12410 kPa) at 6
and the gas is slightly higher than this, 200
It is injected with a pressure exceeding 0 ps 1 (13790 kPa).

For example, glass- and mica-filled nylon, ABS, and polycarbonate (trade name Lexan) are near the upper end of this range, at 3,500 to 7,000 psi (
A higher molten resin pressure of the order of 24,130 kPa to 48,270 kPa) is preset, and the preset pressure of the gas at the indicator sensor 90 again exceeds this molten resin pressure.

Gas injection in the sprue bushing 26 can be used for various gas supply devices, and can also be used with the gas supply device 2.
8 can also be used to inject gas at locations other than the sprue bushing, but a preferred combination is to use the constant gas pressure of the gas supply device 28 to inject gas at the sprue bushing. These two features are particularly compatible in order to obtain better molded parts. The flow of molten resin is carried out at the sprue bushing.
In addition, under pressure that allows gas injection at a constant pressure,
Still very viscous, effective core voiding to the molded parts and smooth surfaces without the need for finishing are achieved.

It should be understood that the injection molding apparatus and method have been described above for illustrative purposes and are not intended to limit or modify the invention. The scope of the invention is set forth in the appended claims.

Finally, to facilitate understanding of the invention, a summary of the invention is provided.According to the invention, there is provided a method and apparatus for making plastic injection molded parts having a smooth surface or skin and a hollow core. The thermoplastic material is then injected as a molten stream into the mold cavity through a sprue bushing secured to the mold.

At the same time, an unmetered amount of inert gas is passed through the thermoplastic material substantially concentrically with the melt flow and at a pressure sufficient to form a gas cavity in the melted material within the mold. It is then introduced into the molten stream through the adapter at the sprue bushing. Adapters can also be added to existing sprue bushings for retrofitting into existing molds.

During injection of the plastic and cooling in the mold, the gas is maintained at a predetermined and appropriately high pressure to hold the plastic against the mold surface until it becomes self-supporting. This gas returns through the sprue bushing and adapter and is exhausted from the mold before the mold is opened. Gas Pressure to the Mold A suitable preset high pressure is maintained in the gas supply by a large cylinder with a volume displacement member inside that is controlled by a pressure sensor in the gas line, resulting in a suitable preset gas pressure in the cavity. is maintained.

[Brief explanation of the drawing]

FIG. 1 is a partial elevational view, partially in section, schematically illustrating the mold with sprue bushing, the sprue bushing adapter, the rotary screw injection molding machine and the compressed gas supply device; Yes; FIG. 2 is an enlarged partial sectional view taken along line 2-2 of FIG. 1; FIG. 3 is an enlarged partial sectional view taken along line 3-3 of FIG. 1; and FIG. 4 are schematic diagrams showing another embodiment of the present invention applied to a mold having four openings in the mold cavity. 10-Mold half-closed (fixed side) 12.-Mold half-closed (movable side) 14-Cavity 16-Plastic parts 18-.
Outer shell 20 - Core 22 - Injection molding machine 24 - Adapter 26 - Sprue bushing 28 - Gas supply device
30-Head 38-Sprue passage 42-Nozzle 51-Nozzle seat 52-Web 54-Through passage 60-Probe 62-Gas passage 64-Gas input low passage 6 Low gas discharge passage 82-Chamber 90-Gas pressure indicator sensor 92-Controller 96- Piston rod 9
8-Hydraulic cylinder 99-Chamber wall 100--Seal 104-Supply tank Applicant's attorney Furuya
Same as Kaoru Takahiko Mizobe Same as Satoshi Furuyapig-4

Claims (1)

[Scope of Claims] 1. A mold, a sprue means carried by the mold and having a sprue passage opening into a mold cavity in the mold, a gas supply device, and a sprue means carried by the mold, and a gas supply device, means for injecting molten plastic into said cavity, said plastic injection means having a nozzle, said plastic injection means cooperating with said mold in operation; a gas injection means disposed between a nozzle and the sprue passage, the gas injection means being configured to connect with the gas supply device and injecting gas into the molten plastic passing through the sprue passage; An injection molding machine comprising a gas inlet opening into the sprue passage. 2. The sprue means is a sprue bushing that is detachably provided on the mold, and the gas injection means is an adapter that is provided on the sprue bushing at an end that engages with the nozzle farther from the cavity. An injection molding machine according to claim 1. 3. The injection method of claim 2, wherein the adapter has a through passage that directs the flow of molten plastic from the nozzle to the sprue passage, and wherein the gas inlet is in direct communication with the flow of molten plastic in the sprue passage. Molding machine. 4. The adapter has a gas inlet passage and a gas exhaust passage, both of which communicate with the gas injection opening.
The injection molding machine according to claim 3. 5. The injection molding machine of claim 3, wherein the gas injection opening is substantially concentric with the sprue passage and substantially open in the direction of flow of molten plastic through the adapter and the sprue bushing. 6. The adapter has a generally torpedo-shaped web extending across the adapter passage, the web having a gas inlet passage and a gas exhaust passage, both of which communicate with the gas injection passage. 6. The injection molding machine of claim 5, wherein the gas injection passage defines the gas injection opening opening substantially concentrically with the flow of the molten plastic. 7. The injection molding machine of claim 6, wherein the gas injection passage extends substantially concentrically into the sprue passage. 8. The injection molding machine of claim 2, wherein the adapter includes a gas injection probe projecting into a sprue passage in the sprue bushing. 9. The sprue means is a standard sprue bushing made of hardened steel and has a head portion with a polished sprue passage and nozzle seat, and the adapter is provided in the head portion, and the adapter is also made of steel. a nozzle seat that engages with the nozzle;
An injection molding machine according to claim 1. 10 a mold, a sprue means carried by the mold and having a through-sprue passageway opening into a mold cavity in the mold, a gas supply device, and a gas supply device carrying a gas into the mold cavity through the sprue means; a gas-assisted method for molding a plastic part having an outer shell and a hollow core using a molding machine comprising means for injecting a stream of molten plastic, the plastic injection means having a nozzle; A method characterized in that a gas is injected into the flow of molten plastic at the sprue means downstream substantially in the direction of the flow of the molten plastic. 11. Introducing a gas into the plastic at a preselected pressure that is greater than the injection pressure of the molten plastic at the point where the gas is introduced until the shell has cooled sufficiently to become self-supporting. a gas-assisted injection molding method for plastic parts, etc. having an outer shell and a hollow core, the method comprising: maintaining a pressure in said core of said preselected pressure; storing the molten plastic in a volumetric chamber, the amount being greater than that needed to make the part, and introducing the molten plastic into the mold via a gas injection region where gas from the chamber is introduced into the plastic. Introducing gas from the chamber into the region at the preselected pressure immediately after starting the injection and molten plastic first enters the region, and detecting any fluctuations in the gas pressure. monitoring the pressure of gas in the chamber while being discharged from the chamber; and automatically reducing the volume of the chamber in response to detection of a variation in gas pressure from the preselected pressure and discharging the gas from the chamber. compensating for the amount of gas that has been released, thus maintaining the pressure of the preselected gas substantially constant until plastic injection is complete and the shell is self-supporting; A method characterized in that a constant preselected gas pressure is maintained during injection and cooling of the plastic by cutting off the gas supply and evacuating the core in order to depressurize the shell. 12. said quantity of gas is delivered to said variable volume chamber at a pressure lower than said preselected pressure, and then the volume of said chamber is reduced prior to beginning introduction of gas into said molten plastic; compressing the quantity of gas to the preselected pressure;
The method according to claim 11. 13. The pressure of the preselected gas is at least about 20
12. The method of claim 11, wherein the pressure is greater than 00 psi (13790 kPa). 14. The method of claim 11, wherein gas is injected into the plastic at a sprue bushing of the mold. 15. Plastic is injected into a mold and gas is introduced into the plastic at a preselected pressure higher than the injection pressure of the molten plastic, and the core is cooled sufficiently to make the shell self-supporting. A gas supply device for use in gas-assisted injection molding, such as plastic parts having an outer shell and a hollow core, in which the pressure of the gas is maintained at a pressure greater than that required for making the part. means for supplying a large quantity of gas at said preselected pressure; a storage chamber for storing said quantity of gas; means for detecting deviation of gas pressure from said preselected pressure; After initiation, the volume of the chamber is automatically reduced in response to the detection of fluctuations in gas pressure to compensate for the gas released from the chamber, so that the plastic injection is finished and the shell is self-supporting. means for maintaining the pressure of said preselected gas substantially constant until said preselected gas is evacuated, means for blocking the introduction of gas into said plastic, and means for evacuating said core to depressurize said outer shell. A gas supply device characterized by: 16 said gas supply means comprises a relatively low pressure gas source, said low pressure gas being supplied to said chamber at said low pressure, said means for reducing the volume of said chamber bringing said quantity of gas to a preselected pressure; 16. The gas supply device according to claim 15, wherein the gas supply device compresses the gas to . 17. The pressure of the preselected gas is at least about 20
16. The gas supply device of claim 15, wherein the gas supply device is greater than 00 psi (13790 kPa). 18. The gas supply device of claim 15, wherein the means for reducing the volume of the chamber compresses a volume displacement member movable into the chamber. 19. Claim in which the member has no sliding seal on the wall of the storage chamber and no frictional engagement with the wall, and the member passes through an opening in the wall of the chamber and the opening is provided with a seal. Item 15. Gas supply device according to item 15. 20. The member is moved by a hydraulic cylinder, the seal is lubricated by hydraulic fluid within the cylinder, and the member is moved by a hydraulic cylinder actuated by a controller responsive to pressure changes in the chamber. Gas supply device as described. 21 further comprising a sprue bushing of the mold and a gas injection adapter disposed between the sprue bushing and a nozzle of a plastic injection molding machine, the sprue bushing having a sprue passage therein; 16. An adapter as claimed in claim 15, having a gas inlet connected to the storage chamber and opening into the sprue bushing for injecting gas into the molten plastic passing through the sprue bushing. Gas supply equipment.