Patent Application
20250121546
The present invention relates to an injection device that injects gas into an injection material to mold a foam molded article, an injection molding machine including such an injection device, and a foam molding method.
An injection molding machine that molds a foam molded article using gas such as nitrogen gas or carbon dioxide gas as a physical foaming agent is generally configured as follows, for example, as described in Patent Literature 1. First, an injection device of the injection molding machine includes a heating cylinder and a screw, and the heating cylinder has a plurality of zones according to the shape of the screw. That is, the heating cylinder has a plasticization zone where the resin is plasticized on an upstream side, a starvation zone where a resin pressure decreases on a downstream side of the plasticization zone, and a compression zone where the resin is compressed on the downstream side of the starvation zone. The heating cylinder is provided with a gas injection port corresponding to the starvation zone, so that gas is supplied to the resin and kneaded with the resin.
The resin is melted in the plasticization zone as being fed downstream by the screw in the heating cylinder. Then, the resin pressure is decreased in the starvation zone, and the gas is supplied. The resin supplied with the gas is kneaded and compressed in the compression zone, and metered. When the resin that is kneaded and compressed with the gas is injected into a mold, the gas foams in the mold. That is, a foam molded article is obtained.
In the injection molding machine for foam molding, the gas is supplied into the resin in the starvation zone. The starvation zone does not necessarily mean that the resin pressure has dropped to an appropriate pressure. This causes a problem that an amount of gas supplied to the resin becomes non-uniform. Further, when the gas is supplied in a state where the resin pressure is high, there is a risk that the resin enters the gas injection port, that is, so-called vent-up occurs. An object of the present disclosure is to stably supply gas into a resin so as to obtain a good foam molded article.
Other problems and novel features will become apparent from description of the present description and the accompanying drawings.
The present inventors have found that the above problem can be solved by providing an injection device having the following configuration. That is, an injection device according to an embodiment of the present invention includes a heating cylinder having a gas injection port, a screw, a gas supply device, and a control unit. The interior of the heating cylinder is divided into a plurality of zones according to the shape of the screw, including a plasticization zone on an upstream side, a starvation zone on a downstream side of the plasticization zone, and a compression zone on the downstream side of the starvation zone. The gas injection port is provided with an injection valve, and gas is supplied into the heating cylinder in the starvation zone. The heating cylinder includes a pressure sensor. The control unit is configured to control the injection valve based on a resin pressure detected by the pressure sensor.
According to the present disclosure, it is possible to provide an injection device that can prevent vent-up and properly supply gas into a resin to obtain a non-defective foam molded article, an injection molding machine including the injection device, and a foam molding method.
Hereinafter, specific embodiments will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments. In order to clarify the description, the following description and the drawings are simplified as appropriate. In the drawings, the same elements are denoted by the same reference numerals, and repeated description thereof is omitted as necessary. In addition, hatching may be omitted to avoid complicating the drawings.
An injection device according to the present embodiment includes:
An injection molding machine according to the present embodiment includes:
A foam molding method according to the present embodiment in which gas is supplied to and kneaded with a resin, and the resin containing the gas is injected to form a foam molded article in an injection device,
As shown in
The fixed platen 7 and the movable platen 8 of the mold clamp device 2 are provided with a fixed mold 13 and a movable mold 14, respectively. When the toggle mechanism 11 is driven, the molds 13 and 14 are clamped. Alternatively, the molds are opened and closed.
The injection device 3 according to the present embodiment is an injection device for foam molding using a physical foaming agent, that is, a gas such as nitrogen gas or carbon dioxide gas. The injection device 3 is shown in
The heating cylinder 17 is provided with a gas injection port 25 through which a gas is supplied. The gas injection port 25 is provided at a position corresponding to the starvation zone 21 when the screw 18 is at a forward position, that is, a screw position at the start of metering. The screw 18 is retracted when the metering process is performed, and the starvation zone 21 is also retracted. In this embodiment, even when the screw 18 reaches a metering completion position, the gas injection port 25 remains in the starvation zone 21. That is, the gas from the gas injection port 25 is normally supplied to the starvation zone 21.
A gas supply device 27 described below is connected to the gas injection port 25, so that gas at a constant pressure is supplied. The injection device 3 according to the present embodiment is characterized in that an injection valve 28 for opening and closing the gas injection port 25 is provided in the gas injection port 25. The injection valve 28 is controlled by the controller 4, and the gas can be efficiently supplied into the resin by appropriately opening and closing the injection valve 28. Further, it is also possible to prevent vent-up in which resin enters the gas injection port. The controller 4 stores a set value used in controlling the injection valve 28, that is, a first threshold value.
The gas supply device 27 includes a gas cylinder 29 that is a gas supply source, and a pressure reducing valve 31 that is configured to reduce the pressure of the gas from the gas cylinder 29 to an appropriate pressure. Although only one gas cylinder 29 is shown in
In the injection device 3 according to the present embodiment, the heating cylinder 17 is provided with a pressure sensor 36. This is also a feature of the present embodiment. The pressure sensor 36 is provided near the gas injection port 25 in the heating cylinder 17. Specifically, when the flight of the screw 18 is considered as a reference, the pressure sensor 36 is provided from the downstream side for one flight round to the upstream side for one flight round around the position where the gas injection port 25 is provided. As described above, the gas injection port 25 is disposed so as to continue to be located in the starvation zone 21 from the start to the completion of the metering. The pressure sensor 36 is also disposed in the starvation zone 21 from the start to the completion of the metering. Accordingly, the pressure sensor 36 continues to detect the resin pressure in the starvation zone 21. The pressure sensor 36 is connected to the controller 4, and the resin pressure is sent to the controller 4.
In the injection device 3 according to the present embodiment, as shown in
<Foam Molding Method according to Present Embodiment>
A method of molding a foam molded article by the injection molding machine 1 (see
A state in which a molding cycle is continuously performed will be described. The injection device 3 according to the present embodiment starts the metering process (step S1). That is, the screw 18 is rotated under the command of the controller 4 (see
Since the molding cycle is continuously performed, the resin in the previous molding cycle remains in the heating cylinder 17. Therefore, along with the start of rotation of the screw 18, the resin is plasticized in the plasticization zone and starts to be fed downstream. The resin in the plasticization zone starts to be sent to the starvation zone 21. The resin in the starvation zone 21 starts to be sent to the compression zone 22. The resin in the compression zone 22 starts to be metered at a tip end of the screw 18. That is, the resin in each of the zones 20, 21, . . . starts to flow to the downstream side as a whole.
When the metering process is started, as shown in
After executing step S3 or step S4, the controller 4 executes step S5. That is, it is checked whether the screw position of the screw 18 (see
In step S5, when the controller 4 determines that the screw position of the screw 18 reaches the metering completion position, step S6 is executed. That is, the injection valve 28 (see
In the metering process of the foam molding method according to the present embodiment, the injection valve 28 is closed when the metering process is completed. That is, the control unit closes the injection valve when the completion of the metering is detected in the injection device. Accordingly, the gas is not unnecessarily supplied into the heating cylinder 17 until the start of the next metering process, and the consumption of the gas can be reduced. However, the injection valve 28 can be maintained in an open state at the completion of the metering process. In this case, the gas can be supplied immediately after the start of metering.
The present embodiment can be variously modified.
For example, as shown in injection devices according to second and third embodiments below, in the injection device according to the embodiments, it is also preferable that a plurality of gas injection ports are provided in the heating cylinder, an injection valve is provided in each of the gas injection ports, and the injection valves are controlled by the control unit.
Further, as shown in injection devices according to second to fifth embodiments below, it is also preferable that the heating cylinder is provided with a plurality of pressure sensors.
<Injection Device according to Second Embodiment>
The embodiment can be variously modified, and
When the metering process is performed by the injection device 3A according to the second embodiment, the first injection valve 28A is controlled to be opened and closed based on the resin pressure detected by the first pressure sensor 36A, and the second injection valve 28a is controlled to be opened and closed based on the resin pressure detected by the second pressure sensor 36a. At the start of the metering, since the first and second gas injection ports 25A, 25a are both located in the starvation zone 21, the gas can be supplied from the first and second gas injection ports 25A, 25a, resulting in high efficiency.
That is, when the screw is located at the screw position at the start of the metering, at least two of the plurality of pressure sensors are preferably located in the starvation zone.
As the metering progresses, when the screw 18 is retracted and the first gas injection port 25A leaves the starvation zone 21, that is, enters the compression zone 22, the resin pressure detected by the first pressure sensor 36A inevitably exceeds the first threshold value. Accordingly, the controller 4 closes the first injection valve 28A. The controller 4 may perform determination based on the screw position of the screw 18, and close the first injection valve 28A without checking the resin pressure.
<Injection Device according to Third Embodiment>
That is, when the screw is located at the screw position at the start of the metering, at least one of the plurality of pressure sensors is preferably located in the starvation zone, and at least one of the plurality of pressure sensors is preferably located in the plasticization zone.
When the metering is started in the injection device 3B according to the third embodiment, only the first gas injection port 25B and the first pressure sensor 36B are located in the starvation zone 21 immediately after the start. Accordingly, only the first gas injection port 25B supplies the gas when the resin pressure becomes equal to or less than the first threshold value. However, when the screw 18 is retreated as the metering progresses, the second gas injection port 25b and the second pressure sensor 36b also enter the starvation zone 21 as shown in
<Injection Device according to Fourth Embodiment>
That is, the injection device according to the fourth embodiment is another example in which, when the screw is at the screw position at the start of the metering, of the plurality of pressure sensors, at least one is located in the starvation zone, and at least one is located in the plasticization zone.
When the metering process is performed in the injection device 3C according to the fourth embodiment, the determination of opening and closing the injection valve 28 can be precisely controlled using not only the resin pressure detected by the first pressure sensor 36C but also the resin pressure detected by the second pressure sensor 36c. During the metering, the resin is sent from the plasticization zone 20 to the starvation zone 21. However, if the resin pressure in the plasticization zone 20 is too high, an amount of the resin sent to the starvation zone 21 increases temporarily, which may cause a phenomenon in which the resin pressure in the starvation zone 21 increases in a short period of time. Therefore, the controller 4 can monitor the resin pressure detected by the second pressure sensor 36c and close the injection valve 28 when the resin pressure exceeds a second threshold value. As a result, the vent-up can be prevented in advance.
<Injection Device according to Fifth Embodiment>
That is, the injection device according to the fifth embodiment is another example in which at least two of the plurality of pressure sensors are located in the starvation zone when the screw is located at the screw position at the start of the metering. It is also preferable that of the plurality of pressure sensors, at least one is provided upstream of the gas injection port, and at least one is provided downstream of the gas injection port.
When the metering process is performed in the injection device 3D according to the fifth embodiment, control can be performed such that the injection valve 28 is closed when either one of the resin pressures detected by the first and second pressure sensors 36D and 36d exceeds the first threshold value. Further, more advanced control can be performed. For example, the control can be performed such that the injection valve 28 is closed when a rate of increase in the resin pressure detected by the first pressure sensor 36D exceeds a third threshold value or when a rate of increase in the resin pressure detected by the second pressure sensor 36d exceeds a fourth threshold value. This is because when there is a large change in the resin pressure on each of the upstream side and the downstream side of the gas injection port 25, the risk of the vent-up increases.
Various modifications are possible for the injection device 3 according to the present embodiment. For example, the number of the gas injection ports 25 may be three or more, and the number is not limited. Similarly, the number of the pressure sensors 36 may be three or more, and the number is not limited.
Although the invention made by the present inventors is specifically described based on the embodiments, it is needless to say that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the invention. The plurality of examples described above may be appropriately combined.
According to the present disclosure, it is possible to provide an injection device that can prevent vent-up and properly supply gas into a resin to obtain a non-defective foam molded article, an injection molding machine including the injection device, and a foam molding method.
Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. The present application is based on Japanese Patent Application No. 2021-186866 filed on Nov. 17, 2021, and the contents thereof are incorporated herein as reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-186866 | Nov 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/034845 | 9/16/2022 | WO |
