Injection device and gas dissolution method of injection device

After the injection shaft moves backward and the gas is supplied into the injection chamber, it is desired to accurately control the gas supply amount in the injection device in which the injection shaft is moved forward to compress and dissolve the gas in the molding material in the injection chamber. An injection device of the disclosure supplies a gas into an injection chamber via a gas supply hole which passes through an injection shaft and is opened at a tip surface of the injection shaft. The injection device and a gas dissolution method thereof according to the disclosure perform backward and forward movement of the injection shaft for a plurality of cycles. The injection device of the disclosure has at least one seal ring and at least one piston ring aligned in an axial direction on an outer circumferential surface of the injection shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serial no. 2019-203819, filed on Nov. 11, 2019, Japan application serial no. 2020-103847, filed on Jun. 16, 2020, and Japan application serial no. 2020-103848, filed on Jun. 16, 2020. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to an injection device of an injection molding machine which injects a molding material in which a gas is compressed and dissolved to obtain a molded product, and a gas dissolution method of the injection device.

Related Art

As an injection device provided in an injection molding machine, as disclosed in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 3-97518), Patent Document 2 (Japanese Patent Publication No. 2615334), and Patent Document 3 (US 2018-0133940 A1), a so-called preplasticizing injection device is conventionally known to be separately provided with a plasticization part for plasticizing a thermoplastic molding material by a plasticization screw, and an injection part for pushing and injecting a molten molding material plasticized by the plasticization part into a mold by an injection shaft. In addition, as disclosed in Patent Document 3, for example, a preplasticizing injection device is also known to be separately provided with a mixing part for mixing a thermosetting molding material and an additive by a mixing shaft, and an injection part for pushing and injecting a liquid molding material mixed by the mixing part into a mold by an injection shaft. Moreover, for example, a preplasticizing injection device is also known to be separately provided with a mixing part for mixing a thermosetting molding material and an additive by a static mixer, and an injection part for pushing and injecting a liquid molding material mixed by the mixing part into a mold by an injection shaft. For example, an injection plunger or an injection screw is used as the injection shaft.

As another injection device, an in-line screw injection device is conventionally known to perform both plasticization and injection with one injection shaft. Further, an in-line screw injection device is also known to perform both mixing and injection with one injection shaft. For example, an in-line screw is used as the injection shaft.

Regarding the injection control of a general injection part, in an injection process, the moving speed of the injection shaft is preferentially controlled, and the injection shaft is greatly moved forward to inject the molding material into the mold; afterwards, in a pressure holding process, the pressure applied to the injection shaft is preferentially controlled to replenish the amount of the molding material cooling and shrinking in the mold.

On the other hand, as shown in, for example, Patent Document 4 (Japanese Patent Publication No. 4148583), when the resin to be molded by an injection molding method is a resin having high viscosity and difficult to mold, it is known that a gas is dissolved in the difficult-to-mold resin under high pressure to reduce the viscosity of the difficult-to-mold resin. Moreover, as a method of dissolving the gas in the difficult-to-mold resin, Patent Document 4 discloses a method of directly supplying a gas from a gas cylinder to the difficult-to-mold resin, and a method of pressurized supply by using a plunger pump or the like.

However, according to the study by the inventors of the disclosure, in an injection part of a conventional injection device, if moving an injection shaft backward and forward in an injection chamber accommodating a molding material is applied as a means for compressing and dissolving a gas supplied into the injection chamber in the molding material in the injection chamber, it has been found that it may be difficult to accurately control the gas supply amount. The disclosure has been made in view of the above circumstances, and it is an objective of the disclosure to provide an injection device capable of compressing and dissolving a gas in a molding material by an injection shaft while controlling the supply amount accurately in the injection device. Another objective of the disclosure is to provide a gas dissolution method of an injection device which can realize such an injection device.

SUMMARY

An injection device of the disclosure injects a molding material into a mold. The injection device includes an injection cylinder, a gas supply device, an injection shaft, an injection driving device, and an injection control device. The injection cylinder is formed with an injection chamber accommodating the molding material. The gas supply device supplies a gas into the injection chamber to compress and dissolve the gas in the molding material supplied into the injection chamber. The injection shaft reciprocates in a cylinder axis direction in the injection chamber and is formed with a gas supply hole penetrating inside the injection shaft. One end part of the gas supply hole is opened on a tip surface forming a part of a wall surface of the injection chamber, and another end part of the gas supply hole is connected to the gas supply device to guide the gas from the gas supply device into the injection chamber The injection driving device causes the injection shaft to reciprocate in the cylinder axis direction. The injection control device controls the injection driving device to move the injection shaft backward and forward in the injection chamber to expand and reduce the injection chamber. After the injection shaft moves backward and the gas is supplied into the injection chamber via the gas supply hole, the injection shaft is moved forward to compress and dissolve the gas in the molding material in the injection chamber.

An injection device of the disclosure injects a molding material into a mold. The injection device includes an injection cylinder, a gas supply device, an injection shaft, an injection driving device, and an injection control device. The injection cylinder is formed with an injection chamber accommodating the molding material. The gas supply device supplies a gas into the injection chamber to compress and dissolve the gas in the molding material supplied into the injection chamber. The injection shaft reciprocates in a cylinder axis direction in the injection chamber. The injection driving device causes the injection shaft to reciprocate in the cylinder axis direction. The injection control device controls the injection driving device to move the injection shaft backward and forward in the injection chamber to expand and reduce the injection chamber. After the injection shaft moves backward and the gas is supplied into the injection chamber, the injection shaft is moved forward to compress and dissolve the gas in the molding material in the injection chamber, and backward and forward movement of the injection shaft is performed for a plurality of cycles when compressing and dissolving a predetermined amount of the gas in the molding material in the injection chamber.

An injection device of the disclosure injects a molding material into a mold. The injection device includes an injection cylinder, a gas supply device, an injection shaft, an injection driving device, and an injection control device. The injection cylinder is formed with an injection chamber accommodating the molding material. The gas supply device supplies a gas into the injection chamber to compress and dissolve the gas in the molding material supplied into the injection chamber. The injection shaft reciprocates in a cylinder axis direction in the injection chamber. The injection driving device causes the injection shaft to reciprocate in the cylinder axis direction. The injection control device controls the injection driving device to move the injection shaft backward and forward in the injection chamber to expand and reduce the injection chamber. After the injection shaft moves backward and the gas is supplied into the injection chamber, the injection shaft is moved forward to compress and dissolve the gas in the molding material in the injection chamber. The injection shaft is provided with at least one piston ring for maintaining a posture and at least one seal ring for preventing leaking of the gas which are aligned in an axial direction on an outer circumferential surface of the injection shaft.

A gas dissolution method of an injection device of the disclosure injects a molding material in which a gas is compressed and dissolved into a mold. The gas dissolution method of the injection device includes the following steps. An injection shaft is moved backward and forward in an injection chamber of an injection cylinder to expand and reduce the injection chamber. After the injection shaft is moved backward and the gas is supplied into the injection chamber, the injection shaft is moved forward to compress and dissolve the gas in the molding material in the injection chamber. When a predetermined amount of the gas is compressed and dissolved in the molding material in the injection chamber, backward and forward movement of the injection shaft is performed for a plurality of cycles.

According to the injection device of the disclosure and the gas dissolution method of the injection device of the disclosure, it is possible to correctly control the gas supply amount. The detailed reason will be described below in accordance with the embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of the disclosure will be described with reference to the drawings by taking a preplasticizing injection device using a thermoplastic resin as a molding material as an example.FIG.1is a view showing a schematic configuration of a preplasticizing injection device1(hereinafter simply referred to as “injection device1”) according to an embodiment of the disclosure. The injection device1includes a plasticization part2which plasticizes a molding material, an injection part3which injects a plasticized molding material in a molten state (hereinafter simply referred to as “molding material”) supplied from the plasticization part2into a cavity space41of a mold4, communication passages3aand5awhich communicate with the internal spaces of the plasticization part2and the injection part3, and a gas supply device8. The plasticization part2and the injection part3are connected by a connection member5. The connection member5is formed with the communication passage5a. An injection molding machine includes at least the injection device1, a mold clamping device (not shown) which mounts the mold4, and a controlling device (not shown) which controls these devices. The injection device1and the mold clamping device are disposed on a machine base (not shown). In the following description, the case where a thermoplastic resin is used as the molding material will be described as an example. In addition to the thermoplastic resin, the molding material may also be a thermosetting resin, a composite material of such resins and metal, or the like, and is not particularly limited. The plasticization part2is a supply device which supplies the molding material to the injection part3. In the following description, the case where the plasticization part2is adopted as the supply device will be described as an example. In addition to the plasticization part2, if the molding material is a thermosetting resin, for example, the supply device may also be a mixing part or the like which, after mixing the thermosetting resin and an additive, supplies the thermosetting resin mixed with the additive to the injection part3, and the disclosure is not particularly limited. Also, the supply device may also be a device which simply supplies the molding material to the injection part3.

The plasticization part2includes a plasticization cylinder20, a plasticization screw21disposed inside the plasticization cylinder20, a rotation driving device22which rotates the plasticization screw21, and a backflow prevention mechanism6. Further, a hopper7for supplying a resin material from the rear end side of the plasticization cylinder20is provided. The hopper7, the plasticization cylinder20, and the backflow prevention mechanism6are attached to a hopper attachment member2a. The rotation driving device22is attached to the backflow prevention mechanism6. A material discharge port of the hopper7and a material supply port of the plasticization cylinder20communicate with each other inside the hopper attachment member2a. The plasticization cylinder20is heated to the inside of the cylinder by, for example, a heater wound around the outer circumference. The mixing part of the preplasticizing injection device using a thermosetting resin material as the molding material includes, for example, a mixing shaft and a mixing cylinder which accommodates the mixing shaft. The mixing cylinder may be cooled by a pipe wound around the outer circumference through which a cooling medium flows.

The inside of the plasticization cylinder20is in communication with an injection chamber34of the injection part3via the communication passage5aof the connection member5and the communication passage3aof the injection part3. A plasticization part side opening5bof the communication passage5ais located on the axial line of the plasticization screw21. The tip of the plasticization screw21is formed in a sharp cone shape. When the rotation driving device22is driven, the plasticization screw21is rotated via a driving transmission mechanism (not shown) arranged in the backflow prevention mechanism6and the hopper attachment member2a. The molding material supplied from the hopper7to the plasticization cylinder20is melted by, for example, the heating of the plasticization cylinder20by the heater and the shear heating generated by compression and rotation of the plasticization screw21. The connection member5is heated to the inside of the member by, for example, a heater wound around the outer circumference. The connection member5of the preplasticizing injection device using a thermosetting resin material as the molding material may be cooled by a pipe wound around the outer circumference through which a cooling medium flows.

The backflow prevention mechanism6is provided to prevent the molding material in the injection chamber34from flowing back into the plasticization cylinder20when pressure is applied to the inside of the injection chamber34by an injection plunger31to be described later. As a specific configuration thereof, for example, as shown in US 2018-0133940 A1, it is possible to adopt a configuration in which the plasticization screw21is moved forward by the backflow prevention mechanism6and the tip of the plasticization screw21closes the plasticization part side opening5bof the communication passage5a. Further, the backflow prevention mechanism6may also adopt an on-off valve such as a check valve, a rotary valve, or a needle valve which closes the communication passage5ain the middle.

The injection part3includes an injection cylinder30, an injection shaft31disposed inside the injection cylinder30, and an injection nozzle32attached to the tip of the injection cylinder30. An injection hole32a, which communicates with the injection chamber34formed inside the injection cylinder30and is opened to the outside, is formed in the injection nozzle32over the entire length of the injection nozzle32. An injection hole on-off valve33which opens and closes the injection hole32ais provided at a tip part of the injection nozzle32. The injection hole on-off valve33may adopt, for example, a check valve, a rotary valve, a needle valve, or the like. The injection cylinder30and the injection nozzle32are heated to the inside of the cylinder by, for example, a heater wound around the outer circumference. In addition, the injection part of the preplasticizing injection device using a thermosetting resin material as the molding material may be cooled by, for example, a pipe wound around the outer circumference of the injection cylinder and the injection nozzle through which a cooling medium flows.

The injection shaft31is the injection plunger31or an injection screw (not shown). Hereinafter, the injection plunger31will be described as an example. A gas supply hole31awhich extends over the entire length of the injection plunger31is provided in a center part of the injection plunger31, and a spring valve31bcapable of opening and closing the gas supply hole31ais accommodated in a tip part (i.e., an end part on the side of the injection nozzle32) of the gas supply hole31a. The gas supply hole31aguides the gas supplied from the gas supply device8into the injection chamber34.

FIG.1schematically shows the above-described configuration of the injection part3.FIG.2is a sectional view showing the above configuration in more detail. It is noted thatFIG.2shows a state in which the injection plunger31is positioned as close to the injection nozzle32as possible. As shown inFIG.2, the spring valve31bis biased toward the right in the figure by a coil spring31s, and if no external force is applied, the biasing force keeps the gas supply hole31aclosed. Also, as shown in the figure, at least one seal ring31cand at least one piston ring31dare fitted on the outer circumferential surface of the injection plunger31having a substantially cylindrical shape to be aligned in the axial direction of the injection plunger31. With the seal ring31cand the piston ring31dsliding on the inner circumferential surface of the injection cylinder30, the injection plunger31can move relatively in the cylinder axial direction of the injection cylinder30while maintaining an airtight state with respect to the injection cylinder30. The seal ring31cmainly prevents the gas in the injection chamber34from leaking between the inner circumferential surface of the injection cylinder30and the outer circumferential surface of the injection plunger31. The piston ring31dmainly aligns the injection plunger31sliding in the injection cylinder30and maintains the posture of the injection plunger31to smooth the movement of the injection plunger31, and meanwhile uniforms the gap between the inner circumferential surface of the injection cylinder30and the outer circumferential surface of the injection plunger31, so that the seal ring31csurely seals all the gaps and prevents the gas in the injection chamber34from leaking from the gaps.

At least one of the seal rings31cmay be made of metal, for example. Exemplarily, three or more metal seal rings31cmay be fitted on the outer circumferential surface of the injection plunger31to be aligned in the axial direction of the injection plunger31. As a specific example,FIG.14shows an example in which three metal seal rings31care fitted to be aligned in the axial direction of the injection plunger31. InFIG.14, elements equivalent to those inFIG.2described above are labeled with the same reference numerals, and descriptions thereof will be omitted unless otherwise necessary (the same applies hereinafter).

At least one of the seal rings31cmay be configured by covering a biasing member with a flexible member, for example. The biasing member is, for example, a spring. The flexible member may have high heat resistance and high abrasion resistance, and may have high sliding properties. The material of the flexible member may include, for example, fluororesin.FIG.15shows an example of the seal ring131cconfigured by covering a biasing member130with a flexible member132. To prevent the seal ring131cconfigured in this manner from being deformed more than necessary and moving from the attachment position, it may be attached to the injection plunger31together with a backup ring131b.

Further, as shown in an example inFIG.16, on the outer circumference of the injection plunger31, at least one annular groove231bmay be formed on a portion on the forward side of the injection plunger31with respect to the seal ring231cto be aligned with the seal ring231cin the axial direction of the injection plunger31.

Hereinafter, returning toFIG.1andFIG.2, the description will be continued. The injection cylinder30may include a cooling device42at the rear end, as shown inFIG.2. The cooling device42suppresses thermal expansion of a rear end part of the injection cylinder30heated by the heater. The gap between the inner circumferential surface of the rear part of the injection cylinder30in which thermal expansion is suppressed and the outer circumferential surface of the injection plunger31facing the inner circumferential surface of the injection cylinder30is suppressed from increasing due to heating of the heater, so that the gas in the injection chamber34is prevented from leaking through the gap.

The cooling device42may be, for example, a scraper ring provided with a cooling pipe43and attached to the rear end part of the injection cylinder30. The scraper ring provided with the cooling pipe43can cool the rear end part of the injection cylinder30by a cooling medium supplied from the inlet of the cooling pipe43and discharged from the outlet. The scraper ring is a device penetrated by the injection plunger31to remove the thin film-shaped molding material attached to the outer circumferential surface of the injection plunger31. The cooling device42may also be a single device other than the scraper ring.

Of the internal space of the injection cylinder30, the space on the front side of the injection plunger31, i.e., the space on the side of the injection nozzle32, is the injection chamber34described above. A driving device holding part35is provided on the rear side of the injection cylinder30, i.e., on the right side inFIG.1, and an injection driving device36is held in the driving device holding part35.

The injection driving device36is formed of, for example, a hydraulic-type piston cylinder device or the like and is configured to move a rod37in the axial direction of the injection plunger31. The rod37is connected to the injection plunger31. Therefore, when the rod37moves as described above, the injection plunger31moves forward and backward. The volume of the injection chamber34decreases when the injection plunger31moves forward, and increases when the injection plunger31moves backward. Herein, the forward movement is a movement to the left inFIG.1, and the backward movement is a movement to the right inFIG.1. The position of the injection plunger31may be detected by a position detector (not shown) such as a linear encoder or a rotary encoder. The driving of the injection driving device36is controlled by an injection control device38. The injection control device38may be included in the above-mentioned control device which controls the entire injection molding machine. The injection control device38may control the injection driving device36based on the detection value of the position detector. In addition to the hydraulic type, the injection driving device36may also be configured as various types such as a pneumatic type or an electric type.

The above-described mold clamping device has a mechanism for opening and closing the mold4and has a structure which applies a sufficient pressure (i.e., a mold clamping force) when the mold4is filled with the molding material. By applying the mold clamping force, the pressure at the time when the melted resin material enters the mold4is not lost, so that the resin material does not come out from the mold4.

The gas supply device8includes, for example, a high-pressure gas cylinder80as a gas supply source which stores a gas such as carbon dioxide, a gas passage81which sends the gas discharged from the high-pressure gas cylinder80into the gas supply hole31aof the injection plunger31via an internal passage (not shown) of the rod37, and a pressure reducing valve82, a pressure gauge83, and a switching valve84which are provided on the gas passage81sequentially from the side of the high-pressure gas cylinder80. The gas supply device8further includes a branch passage85branched from the gas passage81on the downstream side of the switching valve84, i.e., on the side opposite to the high-pressure gas cylinder80, and a switching valve86provided on the branch passage85. The gas passage81forms the gas passage in the disclosure together with the gas supply hole31aof the injection plunger31described above.

In this example, normally, the switching valve84is opened and the switching valve86is closed so that the gas stored in the high-pressure gas cylinder80is sent into the gas supply hole31a. The pressure of the gas sent into the gas supply hole31ain this manner may be set to a desired value through the operation of the pressure reducing valve82. Also, the pressure of the gas may be confirmed by the pressure gauge83. On the other hand, to maintain and manage the injection part3, for example, contrary to the above, it is possible to close the switching valve84and open the switching valve86and discharge to the outside a part of the gas in the gas passage81ranging from the gas supply hole31ato the switching valve86, so as to reduce the pressure of the gas in the gas passage81ranging from the gas supply hole31ato the switching valve86to the atmospheric pressure. Further, the gas supply device8may include at least one pressure control valve92such as a relief valve at a required position of the gas passage81as necessary. It is noted thatFIG.1shows an example in which two pressure control valves92are provided. The pressure control valve92discharges the gas to the outside when the pressure of the gas in the gas passage81exceeds a predetermined pressure value, so that the pressure of the gas in the gas passage81is controlled not to exceed the predetermined pressure value.

The gas supply device8further includes, for example, a flow rate sensor88provided on the gas passage81on the downstream side of the branch passage85, an integrated flow controller89connected to the flow rate sensor88, and an integrated flow monitor90connected to the integrated flow controller89. The flow rate sensor88, the integrated flow controller89, and the integrated flow monitor90form a gas integrated flow measuring device91which measures the integrated flow of the gas, and the gas integrated flow measuring device91is connected to the above-mentioned injection control device38. For example, a signal indicating the integrated flow of the gas sent into the gas supply hole31avia the gas passage81is inputted from the integrated flow monitor90to the injection control device38. The integrated flow controller89and the integrated flow monitor90may be included in the injection control device38or the control device described above. The flow rate sensor88may be a mass flow meter. Further, the gas supply device8may include a mass flow controller capable of detecting the flow rate of the gas in place of the flow rate sensor88and meanwhile controlling the flow rate of the gas. The mass flow controller includes a flow rate sensor, a flow rate control valve, and a control part which controls the flow rate control valve based on the output of the flow rate sensor. The gas supply device8may supply the gas at a desired constant flow rate by the mass flow controller. It is noted that some among the mass flow meters have the function of the integrated flow controller89. Some among the mass flow meters have the function of the integrated flow monitor90. Some among the mass flow controllers have the function of the integrated flow controller89. Some among the mass flow controllers have the function of the integrated flow monitor90. The integrated flow controller89may also utilize the function of the integrated flow controller89included in the mass flow meter or the mass flow controller. The integrated flow monitor90may also utilize the function of the integrated flow monitor90included in the mass flow meter or the mass flow controller.

Hereinafter, the operation of the injection device1will be described with reference toFIG.3toFIG.13. Generally, in injection molding, the processes of mold closing and mold clamping, injection, pressure holding, cooling, measuring, mold opening, and take-out are sequentially performed, and a molded product is obtained by repeating this molding cycle.FIG.3toFIG.13schematically show the states of the injection plunger31, the spring valve31b, and the injection hole on-off valve33over time from the time when the above pressure holding is completed for molding one product, until the pressure holding is performed for molding a next product. While the elements in the figures are all labeled inFIG.3, inFIG.4toFIG.13, only elements requiring description are labeled in order to avoid complication of the figures.

Also, the forward and backward positions of the injection plunger31inside the injection cylinder30are determined by the operation of the injection driving device36controlled by the injection control device38as described above. However, in the following description, unless otherwise necessary, the control of the injection control device38and the operation of the injection driving device36will not be described one by one, but only the operation or position of the injection plunger31may be described.

First, the position of the injection plunger31is in a state shown inFIG.3at the time when the pressure holding process is completed. Further, the injection hole on-off valve33is in a state of opening the injection hole32aof the injection nozzle32. At this time, the molding material remains in the injection chamber34in front of the injection plunger31. Also, at this time, the back flow prevention mechanism6closes the communication passage5a. The operation of the backflow prevention mechanism6is controlled by, for example, the injection control device38but is not limited thereto, and may also be controlled by the control device which controls the operation of the entire injection molding machine.

From the above state, next, as shown inFIG.4, the injection hole on-off valve33formed by, for example, a solenoid valve is changed to a state of closing the injection hole32aof the injection nozzle32. The operation of the injection hole on-off valve33is controlled by, for example, the injection control device38but is not limited thereto, and may also be controlled by the control device which controls the operation of the entire injection molding machine. After the injection hole on-off valve33is changed to the above state, a mold opening process of opening the mold4by the mold clamping device and a take-out process of taking out the cooled molded product from the opened mold4are performed.

Next, as shown inFIG.5, the injection plunger31is moved backward to a predetermined position at a predetermined speed while feeding the gas into the gas supply hole31avia the gas passage81shown inFIG.1. The gas pressure at this time is set to, for example, about 5 MPa or less by the pressure reducing valve82shown inFIG.1. Due to the pressure of this gas and the negative pressure caused by the backward movement of the injection plunger31, the spring valve31bopens the gas supply hole31aagainst the biasing force of the coil spring31s. As a result, the gas is sent from the gas supply hole31ato the internal space (i.e., the injection chamber34) of the injection cylinder30. Since this gas is not so high in pressure as above, it is basically prevented from dissolving in the molding material remaining in the injection chamber34.

Next, as shown inFIG.6, the injection plunger31is moved forward at a predetermined pressure for a predetermined time. Thereby, the gas sent to the injection chamber34is compressed and dissolved in the molding material remaining in the injection chamber34. As the spring valve31bhas the configuration shown inFIG.2, it is possible to prevent the gas sent to the injection chamber34from flowing back to the gas supply hole31a. When the pressure which is the sum of the gas pressure in the injection chamber and the biasing force of the coil spring31sbecomes larger than the gas pressure in the gas supply hole31a, the spring valve31bcloses the gas supply hole31a.

Next, as shown inFIG.7, in the same manner as shown inFIG.5, the injection plunger31is moved backward to a predetermined position at a predetermined speed. Thereby, the gas is sent from the gas supply hole31ato the injection chamber34of the injection cylinder30. Also, in this case, the gas is basically prevented from dissolving in the molding material remaining in the injection chamber34.

Next, as shown inFIG.8, in the same manner as shown inFIG.6, the injection plunger31is moved forward at a predetermined pressure for a predetermined time Thereby, the gas sent to the injection chamber34is compressed and dissolved in the molding material remaining in the injection chamber34.

As described above, the backward movement and the forward movement of the injection plunger31are repeated for a plurality of cycles. Meanwhile, the flow rate sensor88shown inFIG.1detects the flow rate of the gas flowing through the gas passage81, and the integrated flow controller89calculates the integrated flow based on the flow rate of the gas. Then, the integrated flow is monitored by the integrated flow monitor90, and a signal indicating the integrated flow is inputted to the injection control device38. When the integrated flow indicated by this signal reaches a target value (e.g., a desired amount to be supplied into the injection chamber34), the injection control device38controls the operation of the injection driving device36to return the position of the injection plunger31to the position at the time when the initial pressure holding process was completed.FIG.9shows the state at this time. When the integrated flow reaches a predetermined target value, the integrated flow monitor90may output a signal indicating this to the injection control device38. When a signal indicating that the integrated flow has reached the predetermined target value is inputted, the injection control device38may control the operation of the injection driving device36to return the position of the injection plunger31to the position at the time when the initial pressure holding process was completed. The injection control device38may include the integrated flow monitor90and may be inputted with a signal indicating the integrated flow calculated by the integrated flow controller89. When the integrated flow reaches the predetermined target value, the injection control device38may control the operation of the injection driving device36to return the position of the injection plunger31to the position at the time when the initial pressure holding process was completed. The injection control device38may include the integrated flow controller89and the integrated flow monitor90and may be inputted with a signal indicating the flow rate of the gas detected by the flow rate sensor88. An integrated flow is calculated based on the flow rate of the gas, and when the integrated flow reaches the predetermined target value, the injection control device38may control the operation of the injection driving device36to return the position of the injection plunger31to the position at the time when the initial pressure holding process was completed.

Next, the injection control device38opens the communication passage5aand applies a predetermined back pressure to the injection plunger31by the injection driving device36, and meanwhile drives the rotation driving device22ofFIG.1to rotate the plasticization screw21and supplies the molten molding material from the hopper7into the plasticization cylinder20. In addition to directly controlling the driving of the rotation driving device22by the injection control device38in the above manner, a dedicated rotation driving control part which controls the driving of the rotation driving device22may also be provided, and the rotation driving control part may be controlled by the injection control device38. The molding material supplied into the plasticization cylinder20is kneaded and meanwhile sent to the front, i.e., toward the communication passage5a, by the rotating plasticization screw21. The molding material sent from the plasticization part side opening5bof the connection member5into the communication passage5apasses through the communication passage3aand is sent to the injection chamber34of the injection part3.

FIG.10shows the state at this time, and as shown in the figure, the injection plunger31is pushed back by the molding material supplied to the injection chamber34. In the injection chamber34, by mixing the molding material in which the gas has already been compressed and dissolved with the molding material newly supplied to the injection chamber34, the gas supplied to the injection chamber34is compressed and dissolved under high pressure. The injection control device38shown inFIG.1stops the injection plunger31at the position where the measuring is completed, i.e., the position where the measured amount of the molding material reaches a predetermined amount. Reference numeral L1inFIG.9andFIG.10indicates the retracted length of the injection plunger31from the position ofFIG.9to the stop position.

After the above measuring is completed and the backflow prevention mechanism6closes the communication passage5a, the injection control device38moves the injection plunger31forward at a predetermined pressure until the process of injecting the molding material into the mold4is started.FIG.11shows the state after this forward movement has been performed. Reference numeral L2inFIG.10andFIG.11indicates the length of this forward movement. By moving the injection plunger31forward in this manner, the molding material and the gas are further compressed, the dissolution of the gas in the molding material is promoted, and the state in which the gas is compressed and dissolved in the molding material is maintained. Therefore, the molding material is dissolved with the gas, so that the viscosity is lowered and the plasticity is increased.

Next, the injection control device38corrects the position of the injection plunger31at the time of completion of measuring the molding material, which is stored in, for example, an internal memory, as the position after the above forward movement is performed. The position of the injection plunger31at the time of completion of measuring the molding material is the position where the injection plunger31starts to move forward when the molding material is injected into the mold4.

Next, after the injection hole on-off valve33is changed to a state of opening the injection hole32aof the injection nozzle32, the injection control device38moves the injection plunger31forward at a predetermined speed for a predetermined distance as shown inFIG.12. Reference numeral L3inFIG.11andFIG.12indicates the length of this forward movement. By moving the injection plunger31forward in this manner, the molding material in which the gas is dissolved and the viscosity is lowered is injected into the mold4via the injection hole32aof the injection nozzle32.

Then, as shown inFIG.13, the injection control device38performs pressure holding which moves the injection plunger31forward at a predetermined pressure for a predetermined time, until the molding material of a gate portion in the mold4is cooled and solidified. Reference numeral L4inFIG.12andFIG.13indicates the length of the forward movement of the injection plunger31at this time.

The injection control device38or the control device described above may control the injection device1according to the gas dissolution method of the injection device which can realize the injection device1of the disclosure. The injection control device38or the control device described above may control the injection device1according to a program read, by using a reading device (not shown), from a storage medium39storing the program of the injection device which can realize the injection device1of the disclosure.

In the present embodiment, the gas supply hole31apenetrates the injection plunger31. The gas supply hole31ais opened at the tip surface of the injection plunger31and, when the injection plunger31moves backward, communicates with the space in the injection chamber34between the tip surface of the injection plunger31and the molding material in the injection chamber34. In the space communicating with the gas supply hole31a, the pressure in the space is lowered due to the negative pressure resulting from the volume expansion by moving the injection plunger31backward. The gas is supplied into the injection chamber34from the opening of the gas supply hole31aas the pressure in the space becomes smaller than the pressure in the gas supply hole31adue to the negative pressure.

Generally, the molding material remains in the injection nozzle32and the injection chamber34after the pressure holding process. For example, when the gas supply hole31ais opened in the injection nozzle32, or when the gas supply hole31ais opened to the wall surface of the injection chamber34facing the tip surface of the injection plunger31, the gas temporarily pushes away the molding material which covers the opening of the gas supply hole31a, and reaches the space where the internal pressure is lowered by the negative pressure.

The flow rate of the gas flowing from the gas supply hole31ainto the space in which the internal pressure is lowered by the negative pressure decreases as the pressure difference between the pressure in the space where the internal pressure is lowered by the negative pressure and the pressure in the gas supply hole31adecreases, and it is possible that the molding material covering the opening of the gas supply hole31acannot be pushed away. Further, the molding material covering at least a part of the opening of the gas supply hole31amay cause the gas supply from the gas supply hole31ato be stopped halfway.

The amount of the molding material remaining in the injection chamber34after the pressure holding process varies depending on the molding cycle. The amount of the molding material covering the opening of the gas supply hole31aafter the pressure holding process varies depending on the molding cycle. For the above reason, the timing at which the gas supply is stopped may vary depending on the molding cycle. Since the timing at which the gas supply is stopped varies, the supply amount of the gas supplied into the injection chamber34may vary depending on the molding cycle.

In the present embodiment, since the opening of the gas supply hole31ais provided in the tip surface of the injection plunger31, and the injection plunger31is moved backward when the gas is supplied, at least part of the opening of the gas supply hole31ais not covered with the molding material during the gas supply. In the present embodiment, a predetermined amount of gas can be accurately supplied into the injection chamber34for each molding cycle, and the gas supply amount can be correctly controlled.

In the present embodiment, a space is formed in front of the opening of the gas supply hole31aimmediately after the injection plunger31starts to move backward. In the present embodiment, even immediately after the injection plunger31starts to move backward, the gas supply can be started as long as the above-mentioned pressure difference exists, so the stroke in which the injection plunger31moves backward can be shortened.

In the present embodiment, to compress and dissolve a predetermined amount of gas in the molding material in the injection chamber34, the injection plunger31is moved backward and forward for a plurality of cycles.

Generally, the molding material remains in the injection nozzle32and the injection chamber34after the pressure holding process. In the pressure holding process, after injecting the molding material into the mold, a predetermined holding pressure is applied by the injection plunger31to the molding material in the mold through the molding material remaining in the injection chamber34and the molding material remaining in the injection nozzle32. At this time, the molding material in the injection chamber34contracts according to the elasticity of the molding material. When the pressure holding process is completed, the holding pressure is not applied by the injection plunger31. The molding material which has contracted in the injection chamber34generates a repulsive force for returning to its original state. When the pressure holding process is completed, the injection plunger31is pushed back in the backward direction by the repulsive force due to the elasticity of the molding material.

The amount of the molding material remaining in the injection chamber34after the pressure holding process varies depending on the molding cycle. The stroke of the injection plunger31moving in the backward direction due to the repulsion of the molding material after the pressure holding process varies depending on the molding cycle. Due to these variations, the pressure in the injection chamber34before the negative pressure is generated may vary depending on the molding cycle. Afterwards, when the injection plunger31is moved backward, the pressure in the injection chamber34, in which the internal pressure is lowered due to the negative pressure, may also vary depending on the molding cycle. As described above, the gas is supplied into the injection chamber34via the opening of the gas supply hole31adue to the pressure difference. When the injection plunger31is moved backward only once and a predetermined amount of gas is supplied once into the injection chamber34, the gas supply amount may vary depending on the molding cycle.

In the present embodiment, after supplying an amount of gas less than a predetermined amount of gas into the injection chamber34, by repeatedly compressing and dissolving the gas in the molding material in the injection chamber34until the predetermined amount of gas is supplied into the injection chamber34, the predetermined amount of gas can be accurately supplied into the injection chamber34for each molding cycle, and the gas supply amount can be correctly controlled.

In the present embodiment, the stroke of the reciprocating movement of the injection plunger31may be set to be shorter than in the case where the injection plunger31is moved backward and forward only once.

Generally, to set the stroke of the reciprocating movement of the injection plunger31to be longer, it is necessary to form the injection cylinder30to have a greater total length. If the total length of the injection cylinder30is greater, the injection plunger31is separated from the plasticization cylinder20and the injection chamber34and also passes through a part of the injection cylinder30which has a low temperature. In such a case, the molding material in a molten state which is adhered to the injection plunger31in the injection chamber34may be cooled and thinly solidified.

If this solidified molding material remains unevenly on the inner circumferential surface of the injection cylinder30, the gap between the inner circumferential surface of the injection cylinder30and the outer circumferential surface of the injection plunger31becomes uneven. The uneven gap may not be able to be sealed by the seal ring31cattached to the injection plunger31and may cause the gas in the injection chamber34to leak. If the stroke of the reciprocating movement of the injection plunger31is set to be longer, the gas supply amount may not be correctly controlled. On the other hand, if the stroke of the reciprocating movement of the injection plunger31can be set to be shorter, the above issues can be avoided and the gas supply amount can be correctly controlled.

The injection device of the disclosure and the gas dissolution method of the injection device of the disclosure are not limited to the above-described embodiment and may be appropriately changed without departing from the spirit of the disclosure.