JP2024050161A - Manufacturing method and manufacturing device for plastic pipes - Google Patents

Abstract

In the manufacture of multiple resin pipes by fluid-assisted molding, each pipe is molded to have a predetermined wall thickness.
[Solution] The method for manufacturing a resin pipe includes a resin injection step of injecting a different predetermined amount of molten resin (R) into each of a plurality of cavities (12) in a mold, the amount being less than the capacity of the cavity (12), and a gas injection step of injecting a pressurized gas (G) into the molten resin (R) in each cavity (12) during or after the injection of the molten resin (R) into the cavity (12). In the resin injection step, the injection time of the molten resin (R) is adjusted in accordance with the wall thickness of the pipe (100) to be molded in each of the plurality of cavities (12).
[Selected figure] Figure 2

Description

The present invention relates to a manufacturing method and manufacturing device for plastic pipes.

Fluid-assisted molding has been known as a technique for manufacturing hollow resin molded products. In fluid-assisted molding, molten resin is injected into a mold cavity, and then a pressurized fluid is injected into the resin, molding the resin into a hollow shape and forcing it against the molding surface of the mold to solidify. Such a method for manufacturing hollow molded products is disclosed, for example, in Patent Document 1.

Patent Document 1 discloses a method for manufacturing a multi-cavity hollow molded product, which produces multiple hollow molded products in one molding cycle. In this method for manufacturing hollow molded products, a mold with multiple cavities is used, and each cavity in the mold is filled with resin. Then, a sensor placed in each cavity detects that a predetermined amount of resin has been filled, and the filling of the resin is stopped, and gas is then injected into the filled resin.

Japanese Patent Application Laid-Open No. 7-009478

When the multi-cavity manufacturing method disclosed in Patent Document 1 is applied to the manufacture of resin pipes to mold pipes of different lengths, diameters, and external shapes using the multi-cavity method, if molten resin is injected into each cavity in the mold at the same injection speed, the injection time from the start to the completion of injection of molten resin into each cavity will differ. The molten resin injected into each cavity is cooled in the mold and solidifies.

As a result, the degree to which the molten resin solidifies varies in each cavity before the pressurized fluid, such as gas, is injected, and the thickness of the pipes molded at the same time is not stable. Furthermore, when molding pipes with different thicknesses using a multi-cavity mold, it is difficult to mold each pipe with the specified thickness unless it is taken into account that the molten resin continues to solidify even while it is being injected.

The object of the present invention is to mold each pipe with a specified wall thickness when manufacturing multiple plastic pipes using fluid-assisted molding.

To achieve the above objective, the present invention sets the injection time of the molten resin for each cavity, taking into consideration that the solidification of the molten resin progresses even during the injection of the molten resin.

Specifically, the first invention is directed to a method for manufacturing a resin pipe, which uses a mold having multiple cavities to mold multiple resin pipes with different shapes in one molding cycle. The method for manufacturing a resin pipe includes a resin injection process for injecting a different predetermined amount of molten resin, which is less than the capacity of each of the multiple cavities, into each of the multiple cavities, and a fluid injection process for injecting a pressurized fluid into the molten resin in each of the cavities during or after the injection of the molten resin into each of the cavities is completed. In the resin injection process, the injection time of the molten resin is adjusted in accordance with the wall thickness of the resin pipe to be molded in each of the multiple cavities.

The second invention is a method for manufacturing a resin pipe according to the first invention, in which the mold has a first cavity and a second cavity as the cavities. In the resin injection process, the injection time of the molten resin into the first cavity and the injection time of the molten resin into the second cavity are matched.

The third invention is a method for manufacturing a plastic pipe according to the second invention, in which the first cavity and the second cavity are different from each other in at least one of the length, diameter, and bend shape.

The fourth invention is a method for manufacturing a resin pipe according to any one of the first to third inventions, in which, in the resin injection step, a resin injector includes a cylinder and a screw housed in the cylinder, and the screw is advanced from a retracted position to inject the molten resin, thereby individually and sequentially injecting the molten resin into each of the cavities. Furthermore, in the injection step, the amount of the molten resin to be injected into each of the cavities is determined by the advanced position of the screw of the resin injector. And, in the injection step, the injection time of the molten resin into each of the cavities is set by the advanced speed of the screw of the resin injector.

The fifth invention is a method for manufacturing a resin pipe according to any one of the first to third inventions, in which an inert gas is used as the pressurized fluid in the fluid injection step.

The sixth invention is directed to a resin pipe manufacturing device. The resin pipe manufacturing device of the sixth invention includes a mold having a plurality of cavities, a resin injector that injects a different amount of molten resin into each of the plurality of cavities, the amount being less than the capacity of the cavity, a fluid injector that injects a pressurized fluid into the molten resin in each of the cavities during or after the injection of the molten resin into the cavity is completed, a position sensor that detects the advance position of the screw in the resin injector, and a control unit that is connected to the resin injector and the position sensor and controls the operation of the resin injector based on the detection signal of the sensor. The control unit manages the amount of molten resin injected into each of the cavities by the advance position of the screw detected by the position sensor, and sets the injection time of the molten resin into each of the cavities by the advance speed of the screw.

The seventh invention is the resin pipe manufacturing apparatus of the sixth invention, further comprising a first control valve provided for each cavity, which controls the start and stop of injection of the molten resin into the cavity. The control unit is connected to the first control valve, and controls the operation of the first control valve based on the advancement position of the screw detected by the position sensor.

The eighth invention is a resin pipe manufacturing apparatus according to the sixth or seventh invention, further comprising a second control valve provided for each cavity, which controls the start and stop of the injection of the pressurized fluid into the interior of the molten resin injected into the cavity. The control unit is connected to the second control valve, and controls the operation of the second control valve based on the advancement position of the screw detected by the position sensor.

In the first invention, the injection time of the molten resin is adjusted in each of the multiple cavities according to the thickness of the resin pipe to be molded. In each cavity, the injection time of the molten resin is related to the degree of solidification of the molten resin before the pressurized fluid is injected, and the longer the injection time of the molten resin into the cavity, the more the molten resin solidifies. And the more the molten resin solidifies, the thicker the resin pipe becomes. Therefore, by adjusting the injection time of the molten resin in each of the multiple cavities, each pipe can be molded to a predetermined thickness.

In the second invention, the injection time of the molten resin into the first cavity is matched to the injection time of the molten resin into the second cavity. By matching the injection time of the molten resin in each cavity, the degree of solidification of the molten resin that progresses before the pressurized fluid is injected can be made to be the same. This makes it possible to stably mold resin pipes of the same wall thickness in each cavity.

In the third invention, at least one of the length, diameter, and bending shape of the first and second cavities is different from that of the second cavity. If molten resin is injected into the first and second cavities at the same injection speed, the injection time from the start to the end of injection of the molten resin into each cavity will be different. For this reason, it is difficult to mold each pipe with a specified wall thickness unless it is taken into consideration that the solidification of the molten resin progresses even during injection of the molten resin. Therefore, the second invention is particularly effective.

In the fourth invention, the amount of molten resin injected into each cavity is determined by the advancement position of the screw of the resin injector, and the injection time of the molten resin into each cavity is set by the advancement speed of the screw of the resin injector. This makes it easy to adjust the injection time of the molten resin for each cavity. Therefore, the first invention can be implemented effectively.

In the fifth invention, an inert gas is used as the pressurized fluid. Inert gas is a stable gas that is unlikely to undergo chemical reactions. This makes it possible to prevent problems such as resin decomposition and resin burning when manufacturing resin pipes.

In the sixth invention, the control unit manages the amount of molten resin injected into each cavity by the advancement position of the screw detected by a sensor, and sets the injection time of the molten resin into each cavity by the advancement speed of the screw. This makes it easy to adjust the injection time of the molten resin for each cavity. Therefore, the resin pipe manufacturing device is suitable for implementing the first invention.

In the seventh invention, the control unit controls the operation of the first control valve based on the advancement position of the screw detected by the position sensor. The first control valve controls the start and stop of injection of molten resin for each cavity. This makes it possible to use a common resin injector to adjust the injection time of molten resin while managing the amount of molten resin injected for each cavity.

In the eighth invention, the control unit controls the operation of the second control valve based on the advanced position of the screw detected by the position sensor. The second control valve controls the start and stop of the injection of pressurized fluid into the interior of the molten resin for each cavity. In this way, a common fluid injector can be used to inject pressurized fluid into the interior of the molten resin in each cavity.

FIG. 1 is a diagram illustrating a schematic configuration of a resin pipe manufacturing apparatus. FIG. 2 is a timing chart illustrating a method for manufacturing a resin pipe. FIG. 3 is a diagram illustrating a first injection step in the production of a resin pipe. FIG. 4 is a diagram illustrating the second injection step and the first injection step in the production of a resin pipe. FIG. 5 is a diagram illustrating a second injection step in the production of a resin pipe. FIG. 6 is a diagram illustrating a post-treatment in the manufacture of a resin pipe.

Below, exemplary embodiments are described in detail with reference to the drawings. Note that the drawings may show exaggerated or simplified dimensions, ratios, or numbers to facilitate understanding of the present invention. Furthermore, the descriptions "first," "second," ... described below are used to distinguish between words to which these descriptions are attached, and do not limit the number or order of the words.

<<Embodiment>>
The method for manufacturing a resin pipe in this embodiment is a so-called multi-cavity manufacturing method in which a mold having multiple cavities is used to mold multiple resin pipes in one molding cycle. The method for manufacturing a resin pipe in this embodiment uses gas-assisted molding. Gas-assisted molding is a type of fluid-assisted molding that uses gas as the pressurized fluid, and is also called gas injection molding.

- Plastic pipes -
The multiple resin pipes 100 molded in each molding cycle have different shapes. The multiple resin pipes 100 may include two resin pipes 100 having different shapes. Here, "different shapes" does not only mean different external shapes, but also means different lengths, outer diameters, inner diameters, and bend shapes of the pipes.

In the resin pipe manufacturing method of this example, a first pipe 100A and a second pipe 100B are manufactured as the resin pipe 100. The first pipe 100A and the second pipe 100B are hollow parts with a circular cross section that differ in length and bending shape. The first pipe 100A and the second pipe 100B have roughly the same outer diameter and inner diameter, and have approximately the same wall thickness.

The first pipe 100A is a relatively short pipe, and the second pipe 100B is a relatively long pipe. The first pipe 100A and the second pipe 100B are made of, for example, a thermoplastic resin. Examples of materials for the first pipe 100A and the second pipe 100B include polyamide resins (PA) such as nylon 6 and nylon 66, polyphenylene sulfide (PPS), and polypropylene (PP).

-Gas-assisted molding equipment-
The first pipe 100A and the second pipe 100B are manufactured using a gas-assisted molding apparatus 1 shown in Fig. 1. The gas-assisted molding apparatus 1 is an example of an apparatus for manufacturing a resin pipe.

The gas-assisted molding apparatus 1 includes a mold 10, a first gate valve 36, a second gate valve 38, a gas supply line 30, a first gas valve 40, a second gas valve 42, a resin injector 50, a gas injector 60, and a control unit 70. The first gas valve 40 and the second gas valve 42 are each an example of a second control valve. The first gate valve 36 and the second gate valve 38 are each an example of a first control valve.

<Mold>
The mold 10 is a multi-cavity mold having a plurality of cavities 12. The mold 10 has a first cavity 12a and a second cavity 12b as the cavities 12. The first cavity 12a and the second cavity 12b have approximately the same diameter of the cavity 12, but the length and the curved shape of the cavity 12 are different from each other. The first cavity 12a and the second cavity 12b are formed by closing the mold 10. In FIG. 1, the detailed shapes of the first cavity 12a and the second cavity 12b are omitted, and only the difference in length is shown.

The first cavity 12a includes a first gas inlet 14a, a first molding cavity portion 16a, and a first sacrificial cavity portion 18a. The first gas inlet 14a is a cavity for introducing pressurized gas into the first molding cavity portion 16a. The first molding cavity portion 16a is a cavity for molding the first pipe 100A. The first sacrificial cavity portion 18a is a cavity for discharging excess molten resin R from the first molding cavity portion 16a.

In the first cavity 12a of this example, the first gas inlet 14a is connected to one end of the first molding cavity portion 16a, and the first sacrificial cavity portion 18a is connected to the other end of the first molding cavity portion 16a. The first molding cavity portion 16a is defined by the first molding surface 20a that forms the outer surface of the first pipe 100A. The first molding cavity portion 16a is relatively short and has a relatively small volume compared to the second molding cavity portion 16b described below.

The second cavity 12b includes a second gas inlet 14b, a second molding cavity portion 16b, and a second sacrificial cavity portion 18b. The second gas inlet 14b is a cavity for introducing pressurized gas into the second molding cavity portion 16b. The second molding cavity portion 16b is a cavity for molding the second pipe 100B. The second sacrificial cavity portion 18b is a cavity for discharging excess molten resin R from the second molding cavity portion 16b.

In the second cavity 12b of this example, the second gas introduction section 14b is connected to one end side of the second molding cavity section 16b, and the second sacrificial cavity section 18b is connected to the other end side of the second molding cavity section 16b. The second molding cavity section 16b is defined by the second molding surface 20b that molds the outer surface of the second pipe 100B. The second molding cavity section 16b is relatively long and has a relatively large volume compared to the first molding cavity section 16a.

The mold 10 further has a resin supply passage 22. The resin supply passage 22 includes a sprue 24, a first runner 26a, a second runner 26b, a first gate 28a, and a second gate 28b.

The sprue 24 opens onto the outer surface of the mold 10. The first runner 26a and the second runner 26b are each connected to the sprue 24. The first gate 28a is connected to the first runner 26a and opens into the first molding cavity portion 16a. The second gate 28b is connected to the second runner 26b and opens into the second molding cavity portion 16b.

The first gate valve 36 is provided corresponding to the first cavity 12a. The first gate valve 36 controls the start and stop of injection of the molten resin R into the first cavity 12a. In this example, the first gate valve 36 is incorporated into the first gate 28a to form a valve gate. The first gate 28a is opened and closed by the first gate valve 36. The first gate valve 36 operates in response to a control signal input from the control unit 70.

The second gate valve 38 is provided corresponding to the second cavity 12b. The second gate valve 38 controls the start and stop of injection of the molten resin R into the second cavity 12b. In this example, the second gate valve 38 is incorporated into the second gate 28b to form a valve gate. The second gate 28b is opened and closed by the second gate valve 38. The second gate valve 38 operates in response to a control signal input from the control unit 70.

The gas supply path 30 includes a main path 32, a first branch path 34a, and a second branch path 34b. The main path 32 is connected to a gas injector 60. The first branch path 34a and the second branch path 34b are flow paths branched from the main path 32 and are each connected to the mold 10. The first branch path 34a communicates with the first cavity 12a, and the second branch path 34b communicates with the second cavity 12b. The first branch path 34a opens to a portion of the first gas introduction section 14a opposite the first molding cavity section 16a. The second branch path 34b opens to a portion of the second gas introduction section 14b opposite the second molding cavity section 16b.

The first gas valve 40 is provided corresponding to the first cavity 12a. The first gas valve 40 controls the start and stop of the injection of pressurized gas into the first cavity 12a. In this example, the first gas valve 40 is provided in a portion of the first branch path 34a of the gas supply path 30 outside the mold 10. This first branch path 34a is opened and closed by the first gas valve 40. The first gas valve 40 operates in response to a control signal input from the control unit 70.

The second gas valve 42 is provided corresponding to the second cavity 12b. The second gas valve 42 controls the start and stop of the injection of pressurized gas into the second cavity 12b. In this example, the second gas valve 42 is provided in a portion of the second branch path 34b of the gas supply path 30 outside the mold 10. This second branch path 34b is opened and closed by the second gas valve 42. The second gas valve 42 operates in response to a control signal input from the control unit 70.

<Resin molding machine>
The resin injector 50 injects a different predetermined amount of molten resin R into each of the multiple cavities 12, the amount being less than the capacity of the cavity 12. Such incomplete filling of each cavity 12 with the molten resin R is also called a short shot. The resin injector 50 of this example injects a predetermined amount of molten resin R into each of the first cavity 12a and the second cavity 12b.

The amount of molten resin R injected into the first cavity 12a is a first short shot amount that is smaller than the capacity of the first cavity 12a (strictly speaking, the capacity of the first molding cavity portion 16a). The amount of molten resin R injected into the second cavity 12b is a second short shot amount that is smaller than the capacity of the second cavity 12b (strictly speaking, the capacity of the second molding cavity portion 16b). The first short shot amount is smaller than the second short shot amount.

The resin injection machine 50 includes a cylinder 52, a screw 56, a drive unit 58, and a position sensor 59.

The cylinder 52 is a cylindrical member. A nozzle 54 is provided at the tip of the cylinder 52. The nozzle 54 is connected to the outer opening of the sprue 24 in the mold 10. A hopper for supplying resin material such as pellets is provided at the rear of the cylinder 52. A heater is also provided in the cylinder 52. The heater heats the resin material in the cylinder 52. The cylinder 52 heats the resin, which is the molding material, to a molten state, and accumulates the molten resin R inside.

The screw 56 is housed in the cylinder 52 so as to be positioned coaxially with the cylinder 52. The screw 56 rotates and moves back and forth within the cylinder 52. The screw 56 sends the molten resin R in the cylinder 52 forward by rotating, and moves back and forth, displacing the resin within the cylinder 52. The molten resin R sent by the screw 52 is pushed out of the cylinder 52 and injected from the nozzle 54 into the resin supply path 22 (sprue 24).

Positions that the screw 56 can take within the cylinder 52 include a metering completion position P0, a first advance position P1, and a second advance position P2. The metering completion position P0 is the retreated position of the screw 56 when the metering of the molten resin R into the cylinder 52 is completed. The first advance position P1 is the advance position of the screw 56 when the first short shot amount of molten resin R is extruded from the cylinder 52. The second advance position P2 is the advance position of the screw 56 when the second short shot amount of molten resin R is extruded from the cylinder 52.

The drive unit 58 is connected to the screw 56 and rotates and advances and retreats the screw 56. The drive unit 58 includes a belt transmission mechanism and an electric motor. The drive unit 58 operates upon receiving a control signal input from the control unit 70. The position sensor 59 detects the position of the screw 56 in the forward and backward directions within the cylinder 52, that is, the advanced position and the retreated position. The position sensor 59 is provided, for example, in a mechanism part of the drive unit 58 that advances and retreats the screw 56. The position sensor 59 outputs a signal indicating the position of the screw 56 to the control unit 70.

The resin injector 50 injects molten resin R from the nozzle 54 by advancing the screw 56 from the retracted position. In this example, the resin injector 50 injects a first short shot amount of molten resin R from the nozzle 54 by advancing the screw 56 from the metering completion position P0 to the first advance position P1. The resin injector 50 also injects a second short shot amount of molten resin R from the nozzle 54 by advancing the screw 56 from the first advance position P1 to the second advance position P2.

<Gas Injector>
After the injection of the molten resin R into each cavity 12 is completed, the gas injector 60 injects pressurized gas into the molten resin R in that cavity 12. The gas injector 60 is connected to an outer opening of the gas supply path 30 in the mold 10. The gas injector 60 in this example generates pressurized gas as a pressurized fluid. The gas injector 60 then injects the generated pressurized gas at a predetermined pressure into each of the first cavity 12a and the second cavity 12b of the mold 10 via the gas supply path 30.

The gas injector 60 injects pressurized gas into the first cavity 12a after the injection of the molten resin R into the first cavity 12a is completed. The gas injector 60 also injects pressurized gas into the second cavity 12b after the injection of the molten resin R into the second cavity 12b is completed. In this example, the gas injector 60 generates nitrogen gas as the pressurized gas and supplies it to the gas supply path 30. Nitrogen gas is an example of an inert gas.

<Controller unit>
The control unit 70 is connected to the first gate valve 36, the second gate valve 38, the first gas valve 40, the second gas valve 42, the drive device 58, and the position sensor 59. The control unit 70 receives a detection signal from the position sensor 59. The control unit 70 outputs a control signal to the first gate valve 36, the second gate valve 38, the first gas valve 40, the second gas valve 42, and the drive device 58 based on the detection signal from the position sensor 59, and controls the open/closed states of the resin supply path 22 and the gas supply path 30 of the mold 10 and the operation of the resin injector 50.

The control unit 70 is a controller based on a well-known microcomputer. The control unit 70 has a CPU (Central Processing Unit) and a memory. The CPU executes a program for controlling the molding operation of the resin pipe 100 by the gas-assisted molding device 1. The memory stores various programs and data executed by the CPU.

The control unit 70 controls the operation of the first gate valve 36 and the second gate valve 38 based on the advanced position of the screw 56 detected by the position sensor 59. The control unit 70 controls the operation of the first gas valve 40 and the second gas valve 42 based on the advanced position of the screw 56 detected by the position sensor 59. The control unit 70 monitors the advanced position of the screw 56 based on the detection signal of the position sensor 59.

The control unit 70 opens the first gate valve 36 when injecting molten resin R into the first cavity 12a, and closes the first gate valve 36 when injection of molten resin R into the first cavity 12a is completed. The control unit 70 opens the second gate valve 38 when injecting molten resin R into the second cavity 12b, and closes the second gate valve 38 when injection of molten resin R into the second cavity 12b is completed.

The control unit 70 opens the first gate valve 36 with the second gate valve 38 closed, and opens the second gate valve 38 with the first gate valve 36 closed. The control unit 70 controls the opening and closing of the first gate valve 36 and the second gate valve 38 to individually and sequentially inject molten resin R into the first cavity 12a and into the second cavity 12b. In this example, the control unit 70 switches between opening and closing the first gate valve 36 and the second gate valve 38 so that after completing the injection of molten resin R into the first cavity 12a, it injects molten resin R into the second cavity 12b.

The control unit 70 opens the first gas valve 40 when injecting pressurized gas into the first cavity 12a, and closes the first gas valve 40 when the injection of pressurized gas into the first cavity 12a is completed. The control unit 70 opens the second gas valve 42 when injecting pressurized gas into the second cavity 12b, and closes the second gas valve 42 when the injection of pressurized gas into the second cavity 12b is completed. The control unit 70 controls the opening and closing of the first gas valve 40 and the second gas valve 42, thereby starting and ending the injection of pressurized gas into the first cavity 12a and the injection of pressurized gas into the second cavity 12b separately.

In this example, the control unit 70 switches the first gas valve 40 and the second gas valve 42 between open and closed states so as to start injecting pressurized gas into the first cavity 12a when injection of molten resin R into the first cavity 12a is completed, and to start injecting pressurized gas into the second cavity 12b when injection of molten resin R into the second cavity 12b is completed.

The control unit 70 manages the amount of molten resin R injected into each cavity 12 by the advancement position of the screw 56 detected by the position sensor 59. In this example, the control unit 70 manages the first short shot amount injected into the first cavity 12a at the first advancement position P1, and manages the second short shot amount injected into the second cavity 12b at the second advancement position P2.

When the control unit 70 determines, based on the detection signal of the position sensor 59, that the screw 56 has reached the first advance position P1, the control unit 70 completes the injection of the first short shot amount of molten resin R by the resin injector 50. When the control unit 70 determines, based on the detection signal of the position sensor 59, that the screw 56 has reached the second advance position P2, the control unit 70 completes the injection of the second short shot amount of molten resin R by the resin injector 50.

Then, the control unit 70 sets the injection time of the molten resin R for each cavity 12 by the advancement speed of the screw 56. The advancement speed of the screw 56 is set separately to a first speed and a second speed. The first speed is the speed at which the screw 56 moves from the metering completion position P0 to the first advancement position P1. The second speed is the speed at which the screw 56 moves from the first advancement position P1 to the second advancement position P2. The control unit 70 sets the injection time of the molten resin R for the first cavity 12a at the first speed, and sets the injection time of the molten resin R for the second cavity 12b at the second speed.

In the gas-assisted molding apparatus 1 of this example, the first pipe 100A and the second pipe 100B, which are the objects to be molded, are molded to have approximately the same wall thickness. Therefore, the first speed and the second speed are set so as to match the injection time of the molten resin R into the first cavity 12a and the injection time of the molten resin R into the second cavity 12b. In the gas-assisted molding apparatus 1 of this example, since the second molding cavity portion 16b has a larger volume than the first molding cavity portion 16a, the second speed is set faster than the first speed.

- Manufacturing method of plastic pipes -
The resin pipe of this embodiment is manufactured using the gas-assisted molding apparatus 1. The method for manufacturing the resin pipe includes a resin injection step, a gas injection step, and a demolding step. The gas injection step is an example of a fluid injection step.

The resin injection process is a process of injecting a different predetermined amount of molten resin R, which is less than the capacity of each of the multiple cavities 12, into each of the multiple cavities 12. In the resin injection process, the molten resin R is injected into each of the cavities 12 individually and sequentially using a resin injector 50. Then, in the resin injection process, the injection time of the molten resin R is adjusted in each of the multiple cavities 12 according to the wall thickness of the resin pipe 100 to be molded. In the resin injection process of this example, the injection time of the molten resin R into the first cavity 12a and the injection time of the molten resin R into the second cavity 12b are matched.

The gas injection process is a process of injecting pressurized gas into the molten resin R in each cavity 12 after the injection of the molten resin R into that cavity 12 is completed. In the gas injection process, a gas injector 60 is used to start the injection of pressurized gas into each cavity 12 individually and in parallel with each other. Then, in the gas injection process, pressurized gas is injected at a constant pressure into the molten resin R in each of the multiple cavities 12.

The resin injection process in this example includes a first injection process and a second injection process. The gas injection process in this example includes a first injection process and a second injection process. The first injection process and the first injection process are processes for the first cavity, and are performed in this order. The second injection process and the second injection process are processes for the second cavity, and are performed in this order.

As shown in FIG. 2, the production of the resin pipe 100 is started with the first gate valve 36, the second gate valve 38, the first gas valve 40, and the second gas valve 42 of the gas-assisted molding device 1 closed. At this time, the resin injector 50 has already measured the molten resin R into the cylinder 52.

When the production of the resin pipe 100 is started, first, a first injection process is performed by the control unit 70. The first injection process is started at time _t0 when one molding cycle starts, and ends at time _t1 when the injection of a first short shot amount of molten resin R into the first cavity 12a is completed.

In the first injection step, the first gate valve 36 is opened while the second gate valve 38 is kept closed. Then, the control unit 70 causes the resin injector 50 to perform an injection operation. As shown in FIG. 3, in the injection operation, the drive device 58 of the resin injector 50 is operated to advance the screw 56 to the first advance position P1 at a first speed. This causes the molten resin R to be injected from the nozzle 54 of the resin injector 50 through the resin supply path 22 into the first cavity 12a (first molding cavity portion 16a). Then, when the screw 56 reaches the first advance position P1, the first gate valve 36 is closed, completing the injection of the molten resin R into the first cavity 12a.

In this way, the amount of molten resin R to be injected into the first cavity 12a is determined by the advancement position of the screw 56 of the resin injector 50, and a first short shot amount of molten resin R is injected into the first cavity 12a. In this first injection process, the injection time of the molten resin R into the first cavity 12a is set by the advancement speed of the screw 56 of the resin injector 50 according to the thickness of the first pipe 100A. The injection of the molten resin R into the first cavity 12a is completed in a predetermined time (e.g., about 2 seconds) from the start of the injection.

When the first injection process is completed, the second injection process is performed by the control unit 70. The second injection process is started at time _t1 when the first injection process is completed, and ends at time _t2 when the injection of the second short shot amount of molten resin R into the second cavity 12b is completed.

In the second injection process, the second gate valve 38 is opened while the first gate valve 36 is kept closed. Then, as shown in FIG. 4, the drive device 58 of the resin injector 50 continues to operate, increasing the advance speed of the screw 56 and advancing the screw 56 to the second advance position P2 at the second speed. This causes the molten resin R to be injected from the nozzle 54 of the resin injector 50 through the resin supply path 22 into the second cavity 12b (second molding cavity portion 16b). Then, when the screw 56 reaches the second advance position P2, the drive device 58 is stopped, the second gate valve 38 is closed, and the injection of the molten resin R into the second cavity 12b is completed.

In this way, the amount of molten resin R to be injected into the second cavity 12b is determined by the advancement position of the screw 56 of the resin injector 50, and a second short shot amount of molten resin R is injected into the second cavity 12b. In this second injection process, the injection time of the molten resin R into the second cavity 12b is set by the advancement speed of the screw 56 of the resin injector 50 according to the thickness of the second pipe 100B. The injection of the molten resin R into the second cavity 12b is completed in a time (e.g., about 2 seconds) equivalent to the injection time of the molten resin R in the first injection process from the start of the injection.

Furthermore, when the first injection process is completed, the first injection process is performed by the control unit 70. The first injection process is started in parallel with the second injection process. The first injection process is started at time _t1 when the first injection process is completed, and ends at time _t4 when the injection of the pressurized gas into the first cavity 12a is completed.

In the first injection step, the first gas valve 40 is opened while the second gas valve 42 is kept closed. As a result, as shown in FIG. 4, pressurized gas is injected from the gas injector 60 through the gas supply path 30 into the molten resin R in the first cavity 12a at a predetermined pressure. In the first injection step, the injected pressurized gas also reaches a part of the first sacrificial cavity portion 18a. As a result, the molten resin R is pressurized on the first molding surface 20a, while the excess of the molten resin R is pushed out into the first sacrificial cavity portion 18a, forming a hollow portion in the molten resin R in the first molding cavity portion 16a. After a predetermined time has passed since the amount of pressurized gas injected by the gas injector 60 reaches a predetermined amount according to the volume of the first cavity 12a, the first gas valve 40 is closed, and the injection of the pressurized gas into the first cavity 12a is completed.

When the first injection step is completed, the molten resin R is cooled in the first cavity 12a while maintaining the pressure applied to the molten resin R in the first cavity 12a by the pressurized gas. The cooling of the molten resin R in the first cavity 12a progresses gradually while the first injection step is being performed. Therefore, the injection time of the molten resin R into the first cavity is related to the thickness of the first pipe 100A. In other words, the longer the injection time of the molten resin R into the first cavity 12a, the thicker the first pipe 100A tends to be. The molten resin R in the first cavity 12a is solidified by cooling in the mold 10. As a result, the first pipe 100A is molded in the first cavity 12a.

When the second injection process is completed, the second injection process is performed by the control unit 70. The second injection process is started while the first injection process is being performed. The second injection process is started at time _t2 when the second injection process is completed, and ends at time _t5 when the injection of the pressurized gas into the second cavity 12b is completed.

In the second injection step, the second gas valve 42 is opened while the first gas valve 40 is kept open. As a result, as shown in FIG. 5, pressurized gas is injected from the gas injector 60 through the gas supply path 30 into the molten resin R in the second cavity 12b at a predetermined pressure. In the second injection step, the injected pressurized gas also reaches a part of the second sacrificial cavity portion 18b. As a result, the molten resin R is pressurized on the second molding surface 20b, while the excess of the molten resin R is pushed out into the second sacrificial cavity portion 18b, forming a hollow portion in the molten resin R in the second molding cavity portion 16b. After a predetermined time has passed since the amount of pressurized gas injected by the gas injector 60 reaches a predetermined amount according to the volume of the second cavity 12b, the second gas valve 42 is closed, and the injection of the pressurized gas into the second cavity 12b is completed.

When the second injection step is completed, the molten resin R is cooled in the second cavity 12b while maintaining the pressure applied to the molten resin R in the second cavity 12b by the pressurized gas. The cooling of the molten resin R in the second cavity 12b progresses gradually during the execution of the second injection step. Therefore, the injection time of the molten resin R into the second cavity 12b is related to the thickness of the second pipe 100B. In other words, the longer the injection time of the molten resin R into the second cavity 12b, the thicker the wall of the second pipe 100B tends to be. The molten resin R in the second cavity 12b is solidified by cooling in the mold 10. As a result, the second pipe 100B is molded in the second cavity 12b.

Furthermore, when the second injection process is completed, the control unit 70 causes the resin injector 50 to perform a metering operation. The metering operation starts at time _t2 when the second injection process is completed, and ends at time _t3 when a certain volume of molten resin is accumulated in the cylinder 52. In the metering operation, a resin material is supplied from a hopper into the cylinder 52, the resin material is heated by a heater to a molten state, the screw 56 is retracted to the metering completion position P0, and a certain volume of molten resin R is accumulated in the cylinder 52. When the metering operation is completed, the resin injector 50 goes into a standby state.

Thereafter, a demolding process is performed. The demolding process is performed at time _t6 when the molten resin R in the first cavity 12a and the molten resin R in the second cavity 12b are completely solidified. In the demolding process, the mold 10 is opened, and the first pipe 100A and the second pipe 100B are removed from the opened mold 10. Then, as shown in FIG. 6, the excess solid matter 102 and the gate residue 104 in the first gas inlet portion 14a and the first sacrificial cavity portion 18a in the first pipe 100A are cut off. In addition, the excess solid matter 102 and the gate residue 104 in the second gas inlet portion 14b and the second sacrificial cavity portion 18b in the second pipe 100B are cut off.

In this manner, the first pipe 100A and the second pipe 100B can be molded in a single molding cycle. The weight variation of the first pipe 100A and the second pipe 100b thus molded can be suppressed to approximately ±1.5% per molding cycle.

-Features of the embodiment-
In the method for manufacturing a resin pipe according to this embodiment, the injection time of the molten resin R is adjusted in each of the multiple cavities 12 according to the thickness of the resin pipe 100 (first pipe 100A and second pipe 100B) to be molded. In each cavity 12, the injection time of the molten resin R is related to the degree of solidification of the molten resin R before the pressurized gas is injected, and the longer the injection time of the molten resin R into the cavity 12, the more the solidification of the molten resin R progresses. And, the more the solidification of the molten resin R progresses, the thicker the wall of the resin pipe 100 becomes. Therefore, by adjusting the injection time of the molten resin R in each of the multiple cavities 12, it is possible to mold each pipe 100 to a predetermined wall thickness.

In the method for manufacturing a resin pipe of this embodiment, the injection time of the molten resin R into the first cavity 12a is matched to the injection time of the molten resin R into the second cavity 12b. By matching the injection time of the molten resin R in the first cavity 12a and the second cavity 12b, the degree of solidification of the molten resin R that progresses until the pressurized gas is injected can be made to be the same. This makes it possible to stably mold resin pipes 100 (first pipe 100A and second pipe 100B) of the same thickness in the first cavity 12a and the second cavity 12b.

In the manufacturing method of the resin pipe of this embodiment, the length and the curved shape of the first cavity 12a and the second cavity 12b are different from each other. If the molten resin R is injected into the first cavity 12a and the second cavity 12b at the same injection speed, the injection time from the start to the completion of the injection of the molten resin R into each cavity 12 will be different. For this reason, it is difficult to mold each pipe 100 with a predetermined thickness unless it is taken into consideration that the solidification of the molten resin progresses even during the injection of the molten resin R. Therefore, the manufacturing method of the resin pipe of this embodiment is effective.

In the method for manufacturing resin pipes of this embodiment, the amount of molten resin R injected into each cavity 12 is determined by the advancement position of the screw 56 of the resin injector 50, and the injection time of the molten resin R into each cavity 12 is set by the advancement speed of the screw 56 of the resin injector 50. This makes it easy to adjust the injection time of the molten resin R for each cavity 12.

In this embodiment of the method for manufacturing a plastic pipe, nitrogen gas is used as the pressurized fluid. Nitrogen gas is a stable gas that is unlikely to undergo chemical reactions. Therefore, when manufacturing the plastic pipe 100, problems such as resin decomposition and resin burning can be suppressed.

In the gas-assisted molding device 1 of this embodiment, the control unit 70 manages the amount of molten resin R injected into each cavity 12 by the advancing position of the screw 56 detected by the position sensor 59, and sets the injection time of the molten resin R into each cavity 12 by the advancing speed of the screw 56. This makes it easy to adjust the injection time of the molten resin R for each cavity 12. Therefore, the resin pipe manufacturing device is suitable for implementing the resin pipe manufacturing method of this embodiment, which adjusts the injection time of the molten resin R depending on the wall thickness of the resin pipe 100 to be molded in each of the multiple cavities 12.

In this embodiment of the gas-assisted molding device 1, the control unit 70 controls the operation of the first gate valve 36 and the second gate valve 38 based on the advanced position of the screw 56 detected by the position sensor 59. The first gate valve 36 and the second gate valve 38 control the start and stop of the injection of the molten resin R for each cavity 12. In this way, by using a common resin injector 50, the injection time of the molten resin R can be adjusted while managing the amount of molten resin R to be injected for each cavity 12.

In this embodiment of the gas-assisted molding device 1, the control unit 70 controls the operation of the first gas valve 40 and the second gas valve 42 based on the advanced position of the screw 56 detected by the position sensor 59. The first gas valve 40 and the second gas valve 42 control the start and stop of the injection of pressurized gas into the interior of the molten resin R for each cavity 12. In this way, a common gas injector 60 can be used to inject pressurized gas into the interior of the molten resin R in each cavity 12.

Other Embodiments
In the above embodiment, the two resin pipes 100, the first pipe 100A and the second pipe 100B, are described as molding objects, but this is not limited thereto. The gas-assisted molding apparatus 1 and the method for manufacturing a resin pipe using the same may mold three or more resin pipes 100.

In the above embodiment, the first pipe 100A and the second pipe 100B have roughly the same outer diameter and inner diameter, but this is not limited to the above. The first pipe 100A and the second pipe 100B may have different outer diameters and/or inner diameters. In this case, the first pipe 100A and the second pipe 100B may have the same length and/or curved shape.

In the above embodiment, the first pipe 100A and the second pipe 100B have approximately the same thickness, but this is not limited to the above. The first pipe 100A and the second pipe 100B may have different thicknesses. For example, if the thickness of the second pipe 100B is thicker than the thickness of the first pipe 100A, the injection time of the molten resin R into the second cavity 12b may be set longer than the injection time of the molten resin R into the first cavity 12a.

In the above embodiment, in the gas injection process, after the injection of the molten resin R into each cavity 12 is completed, the pressurized gas is injected into the molten resin R in that cavity 12, but this is not limited to the above. In the gas injection process, the pressurized gas may be injected into the molten resin R in each cavity 12 while the injection of the molten resin R into that cavity 12 is being performed.

In the above embodiment, the gas injector 60 has been described as having the function of generating pressurized gas, but this is not limited to the above. The gas-assisted molding device 1 may include a gas generator that generates pressurized gas in addition to the gas injector, and the gas injector 60 may only have the function of sending the pressurized gas generated by the gas generator to the gas supply path 30.

In the above embodiment, the manufacturing method for a resin pipe according to the present invention has been described using gas-assisted molding as an example, but the present invention is not limited to this. The present invention can also be applied to a manufacturing method and manufacturing device for a resin pipe that uses other fluid-assisted molding that uses a pressurized fluid other than gas, such as water-assisted molding that uses a liquid such as water as the pressurized fluid.

As described above, a preferred embodiment has been described as an example of the present invention. However, the present invention is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. It will be understood by those skilled in the art that the above embodiment is an example, and that various further modifications are possible in the combination of each component and each processing process, and that such modifications also fall within the scope of the present invention.

As described above, the present invention is useful for a manufacturing method and manufacturing device for plastic pipes.

G Pressurized gas (pressurized fluid, inert gas)
R Molten resin 1 Gas-assisted molding device (plastic pipe manufacturing device)
10 Mold 12 Cavity 12a First cavity 12b Second cavity 36 First gate valve (first control valve)
38 Second gate valve (first control valve)
40 First gas valve (second control valve)
42 Second gas valve (second control valve)
50 Resin injection machine 52 Cylinder 56 Screw 59 Position sensor 60 Gas injector (fluid injector)
70 Control unit 100 Resin pipe

Claims (8)

A method for manufacturing a resin pipe, comprising the steps of: molding a plurality of resin pipes (100) having different shapes in one molding cycle using a mold (10) having a plurality of cavities (12);
a resin injection step of injecting a different predetermined amount of molten resin (R) into each of the plurality of cavities (12), the amount being smaller than the capacity of the corresponding cavity (12);
a fluid injection step of injecting a pressurized fluid (G) into the molten resin (R) in each of the cavities (12) during or after the injection of the molten resin (R) in the respective cavities (12),
In the resin injection step, an injection time of the molten resin (R) is adjusted in accordance with a wall thickness of the resin pipe (100) to be molded in each of the plurality of cavities (12).
A method for manufacturing a resin pipe comprising the steps of: The method for producing a resin pipe according to claim 1,
The mold (10) has a first cavity (12a) and a second cavity (12b) as the cavity (12),
In the resin injection step, an injection time of the molten resin (R) into the first cavity (12a) and an injection time of the molten resin (R) into the second cavity (12b) are matched.
A method for manufacturing a resin pipe comprising the steps of: The method for producing a resin pipe according to claim 2,
At least one of the length, the diameter, and the bending shape of the first cavity (12a) and the second cavity (12b) is different from each other.
A method for manufacturing a resin pipe comprising the steps of: In the method for producing a resin pipe according to any one of claims 1 to 3,
In the resin injection step,
a resin injector (50) including a cylinder (52) and a screw (56) housed in the cylinder (52), the screw (56) being advanced from a retracted position to inject the molten resin (R), the molten resin (R) being injected individually and sequentially into each of the cavities (12);
the amount of the molten resin (R) to be injected into each of the cavities (12) is determined by the advancement position of the screw (56) of the resin injector (50);
An injection time of the molten resin (R) into each of the cavities (12) is set by an advancement speed of the screw (56) of the resin injector (50).
A method for manufacturing a resin pipe comprising the steps of: In the method for producing a resin pipe according to any one of claims 1 to 3,
In the fluid injection step, an inert gas (G) is used as the fluid (G).
A method for manufacturing a resin pipe comprising the steps of: A mold (10) having a plurality of cavities (12);
a resin injector (50) configured to inject a different amount of molten resin (R) into each of the plurality of cavities (12), the amount being smaller than the capacity of the cavity (12);
a fluid injector (60) for injecting a pressurized fluid (G) into the molten resin (R) in each of the cavities (12) during or after the injection of the molten resin (R) into the respective cavities (12);
a position sensor (59) for detecting an advanced position of the screw (56) in the resin injector (50);
a control unit (70) connected to the resin injector (50) and the position sensor (59) and configured to control the operation of the resin injector (50) based on a detection signal of the position sensor (59),
the control unit (70) manages the amount of the molten resin (R) injected into each of the cavities (12) by the advancing position of the screw (56) detected by the position sensor (59), and sets the injection time of the molten resin (R) into each of the cavities (12) by the advancing speed of the screw (56).
A resin pipe manufacturing apparatus comprising: The resin pipe manufacturing apparatus according to claim 6,
a first control valve (36, 38) provided for each of the cavities (12) and configured to control start and stop of injection of the molten resin (R) into the corresponding cavity (12);
the control unit (70) is connected to the first control valve (36, 38) and controls the operation of the first control valve (36, 38) based on the advanced position of the screw (56) detected by the position sensor (59).
A resin pipe manufacturing apparatus comprising: In the resin pipe manufacturing apparatus according to claim 6 or 7,
a second control valve (40, 42) provided for each of the cavities (12) for controlling start and stop of injection of the pressurized fluid (G) into the corresponding cavity (12);
the control unit (70) is connected to the second control valve (40, 42) and controls the operation of the second control valve (40, 42) based on the advanced position of the screw (56) detected by the position sensor (59).
A resin pipe manufacturing apparatus comprising: