JP7317565B2 - blow molding machine - Google Patents

Description

The present invention relates to a blow molding apparatus.

Patent Literature 1 discloses a blow molding apparatus in which an extruder having a screw feeds a molten resin into a die head and extrudes a parison from a nozzle of the die head. In this type of blow molding apparatus, if the viscosity of the molten resin, which is the raw material of the parison, is low, a problem called drawdown may occur in which the parison cannot maintain a predetermined shape due to its own weight. In order to prevent drawdown, it is good to use a molten resin material with high viscosity, but if the viscosity is increased, the molten resin will be insufficiently kneaded during the process of moving inside the extruder, so the parison will solidify. As a result, unevenness occurs on the inner peripheral surface of the parison.

JP 2008-155568 A

As a means to solve the lack of kneading due to the use of high-viscosity molten resin, there is a method of applying a screw with a high compression ratio, or installing a mixer at the downstream end of the screw to concentrate the molten resin in a short time. For example, a method of vigorously stirring can be considered. However, simply adjusting the compression ratio is not enough to solve the problem of insufficient kneading. In addition, when a mixer is used, intensive stirring for a short period of time causes the temperature of the molten resin to rise significantly due to frictional resistance due to shearing, resulting in degradation of the resin, cross-linking reaction, and the like. Degradation and cross-linking reaction of the resin cause unevenness on the inner peripheral surface of the parison when the parison is solidified.

SUMMARY OF THE INVENTION The present invention has been completed based on the above circumstances, and an object of the present invention is to enable molding of a parison having a smooth inner peripheral surface.

The present invention
An extruder that feeds out the molten resin with a screw,
a die head for forming a parison by extruding the molten resin sent from the extruder downward from a nozzle;
and resistance imparting means for imparting resistance to the molten resin in the extruder to suppress movement in the delivery direction.

The molten resin fed by the screw in the extruder is sheared by the screw by receiving the resistance of the resistance imparting means, so kneading of the molten resin proceeds. The shearing by the screw is not performed intensively in a short time, but is performed over time while being sent to the die head side, so that there is little frictional resistance and there is no fear that the temperature of the molten resin will rise. Therefore, it is possible to mold a parison having a smooth inner peripheral surface without unevenness.

FIG. 2 is a cross-sectional view showing the process of feeding molten resin to the die head side in the blow molding apparatus of Example 1. Cross-sectional view showing a state in which a parison is being molded by extruding molten resin in a blow molding device Front view of resistance member 4 is a front view of a resistance member having a form different from that of FIG. 3

In the present invention, the resistance imparting means may comprise a resistance member having a plurality of through holes formed therein and disposed between the downstream end of the extruder and the die head. According to this configuration, the molten resin is restrained from moving in the feeding direction due to the flow resistance generated when passing through the plurality of through holes. Since the resistance member has a simple shape, the cost can be suppressed.

In the present invention, the die head includes a storage chamber for storing the molten resin, and a movable member that is displaced in a direction to increase the volume of the storage chamber as the molten resin is fed from the extruder to the storage chamber. may be provided, and the resistance applying means may include an urging mechanism that applies an urging force to the movable member in a direction to reduce the volume of the storage chamber. According to this configuration, the molten resin is restrained from moving in the delivery direction by the biasing force applied to the movable member from the biasing mechanism.

In the present invention, the biasing mechanism may include a fluid pressure cylinder that drives the movable member in a direction to decrease the volume of the storage chamber. According to this configuration, the fluid pressure cylinder has both the function of driving the movable member and the function of applying resistance to the molten resin. The structure of the molding device can be simplified.

<Example 1>
A first embodiment embodying the present invention will be described below with reference to FIGS. 1 to 4. FIG. In the following description, the directions shown in FIGS. 1 and 2 are defined as upward and downward as they are.

The blow molding apparatus A of Example 1 comprises an extruder 10 , a die head 22 , an extrusion device 30 and resistance imparting means 50 . The extruder 10 is a device that horizontally feeds the molten resin R toward a die head 22, and includes a case 11, a screw 12 housed in the case 11, and a motor 21 that rotates the screw 12. It is The screw 12 is composed of a shaft portion 13 whose axis is oriented in the horizontal direction (front-to-rear direction) and a helical vane plate 14 provided on the outer periphery of the shaft portion 13 . A gap between the inner peripheral surface of the case 11 and the outer peripheral surface of the shaft portion 13 serves as a delivery path 15 for delivering the molten resin R. The extruder 10 is formed with a delivery port 16 that communicates with the downstream end of the delivery path 15 in the delivery direction.

The upstream end of the screw 12 in the delivery direction serves as a supply section 17, the substantially central portion of the screw 12 in the delivery direction serves as a compression section 18, and the downstream end in the delivery direction of the screw 12 serves as a metering section 19. It's becoming The delivery path 15 is constituted by a spiral groove portion 20 defined by the outer circumference of the shaft portion 13 and the blade plate 14 . The depth of the groove portion 20 in the supply portion 17 (the dimensional difference between the outer diameter of the blade plate 14 and the outer diameter of the shaft portion 13) is the depth of the groove portion 20 in the weighing portion 19 (the outer diameter of the blade plate 14 and the shaft portion 13 is set to a dimension larger than the dimensional difference from the outer diameter of the

The molten resin R supplied into the delivery path 15 at the upstream end of the delivery path 15 is pushed in the axial direction by the blade plate 14 of the rotating screw 12, thereby being pushed and moved in the delivery path 15 from the upstream side to the downstream side. be Further, the molten resin R in the delivery path 15 is kneaded by being sheared by the blade plate 14 while being pushed.

The die head 22 comprises a cylindrical housing 23 with its axis directed vertically, and a cylindrical core 24 coaxially accommodated in the housing 23 . A tubular storage chamber 25 is formed between the inner peripheral surface of the housing 23 and the outer peripheral surface of the core 24 . An inflow passage 26 is provided in the housing 23 . The upstream end of the inflow path 26 is connected to the delivery port 16 of the extruder 10 outside the housing 23 via a later-described resistance member 51 . A downstream end of the inflow path 26 communicates with the storage chamber 25 inside the housing 23 .

An annular slit-shaped nozzle 27 defined by the opening edge of the lower end surface of the housing 23 and the outer peripheral surface of the lower end portion of the core 24 is formed in the lower end surface of the die head 22 . The nozzle 27 communicates with the lower end of the storage chamber 25 . The molten resin R stored in the storage chamber 25 is pushed out downward from the nozzle 27 by the extrusion device 30 . The molten resin R extruded from the nozzle 27 becomes a parison P with its axis directed vertically, which is molded by a mold (not shown) to become a product such as a high-pressure container or a fuel tank.

The extrusion device 30 includes a base 31 fixed to the upper end surface of the housing 23 , an opening/closing cylinder 32 provided on the upper surface of the base 31 , an annular movable member 34 , and a plurality of actuators provided on the upper surface of the base 31 . It is composed of an extrusion cylinder 36 (a fluid pressure cylinder described in the claims) and a hydraulic oil supply/discharge device 40 . The opening/closing cylinder 32 is arranged coaxially with the core 24 and has an opening/closing rod 33 that passes through the base 31 and is integrated with the upper end portion of the core 24 . By driving the opening/closing cylinder 32, the core 24 moves up and down between a closed position (see FIG. 1) that closes the nozzle 27 and an open position (see FIG. 2) that opens the nozzle 27. there is

An upper end region of the storage chamber 25 is an elevating space 35 having an annular shape coaxial with the core 24 and the storage chamber 25 . That is, the elevating space 35 constitutes the storage chamber 25 . A movable member 34 is accommodated in the elevating space 35 so as to be able to ascend and descend. A lower end surface of the movable member 34 faces downward toward the storage chamber 25 . A plurality of extrusion cylinders 36 are arranged to surround the core 24 . The plurality of push-out cylinders 36 have a plurality of push-out rods 37 penetrating through the base 31 and protruding downward. A plurality of pushing rods 37 are arranged so as to surround the core 33 at intervals in the circumferential direction. The lower ends of the plurality of pushing rods 37 are fixed to the upper end surface of the movable member 34 , and the movable member 34 moves up and down by driving the pushing cylinder 36 . When the movable member 34 rises, the volume of the storage chamber 25 increases, and when the movable member 34 descends, the volume of the storage chamber 25 decreases. The movable member 34 constitutes an accumulator 38 .

The hydraulic oil supply/discharge device 40 includes a common flow path 41 , a directional switching valve 43 , a pumping flow path 44 , a pump 45 , a storage tank 46 , a discharge flow path 47 and a throttle valve 48 . The common flow path 41 branches into a plurality of branch paths 42 and is individually connected to a plurality of extrusion cylinders 36 . A directional switching valve 43 (three-way valve) is connected to the end of the shared flow path 41 opposite to the extrusion cylinder 36 . The inflow port of the direction switching valve 43 is connected to the downstream end of the pressure feed passage 44 . A pump 45 is provided in the middle of the pressure-feeding channel 44 , and the upstream end of the pressure-feeding channel 44 is connected to a storage tank 46 . An upstream end of a discharge passage 47 is connected to an outflow port of the direction switching valve 43 . A throttle valve 48 is provided in the middle of the discharge channel 47 , and the downstream end of the discharge channel 47 is connected to a storage tank 46 .

When extruding the parison P from the die head 22 , the movable member 34 is raised in advance so that the downstream end of the inflow path 26 faces the storage chamber 25 . When storing the molten resin R in the storage chamber 25, as shown in FIG. 1, the nozzle 27 is closed and the directional switching valve 43 is switched to the storage mode. In this state, when the molten resin R in the extruder 10 is fed into the storage chamber 25, the pressure of the molten resin R in the storage chamber 25 increases, so the movable member 34 rises and the volume of the storage chamber 25 increases. As a result, the amount of molten resin R stored in the storage chamber 25 increases. As the movable member 34 rises, the working oil in the pushing cylinder 36 passes through the direction switching valve 43 and the throttle valve 48 and is discharged into the storage tank 46 .

After a predetermined amount of molten resin R is stored in the storage chamber 25, as shown in FIG. When the pump 45 is driven in this state, the hydraulic oil in the storage tank 46 is pressure-fed to the extrusion cylinder 36 via the direction switching valve 43, and the driving force of the extrusion cylinder 36 causes the movable member 34 to descend. The volume of chamber 25 is reduced. As a result, the molten resin R in the storage chamber 25 is extruded downward from the nozzle 27 to become the parison P. As shown in FIG.

The resistance applying means 50 is configured with a resistance member 51 and an urging mechanism 54 . The resistance member 51 is provided between the delivery port 16 (downstream end of the delivery path) of the extruder 10 and the upstream end of the inflow path 26 . The resistance member 51 has a plate shape that blocks the flow path of the molten resin R from the delivery port 16 to the inflow path 26 . The resistance member 51 is formed with a plurality of through holes 52 that allow the delivery port 16 and the inflow path 26 to communicate with each other. As the through holes 52, a plurality of independent circular openings may be used as shown in FIG. There may be.

When the molten resin R passes through the through hole 52 of the resistance member 51, the part of the molten resin R on the upstream side of the resistance member 51 (that is, the molten resin R is fed out by the screw 12 in the extruder 10). flow resistance is applied to the Therefore, compared to the case where the resistance member 51 is not provided, the delivery of the molten resin R by the screw 12 in the extruder 10 is suppressed, and the pressure of the molten resin R in the extruder 10 (delivery path 15) is high. .

The biasing mechanism 54 includes the movable member 34, the pushing cylinder 36, and the throttle valve 48 described above. As described above, in the process in which the molten resin R in the extruder 10 is fed into the storage chamber 25 and the movable member 34 rises, the hydraulic oil in the extrusion cylinder 36 passes through the throttle valve 48, thereby 46 is discharged. Here, if the flow path of the hydraulic oil in the throttle valve 48 is narrower than the discharge flow path 47 , when the hydraulic oil passes through the throttle valve 48 Flow resistance is applied to the hydraulic oil at the portion (that is, the portion on the extrusion cylinder 36 side). The flow resistance imparted to the hydraulic oil is transmitted to the molten resin R in the storage chamber 25 via the extrusion rod 37 and the movable member 34, and furthermore, the molten resin R in the extruder 10 (delivery passage 15) is transmitted to As a result, delivery of the molten resin R by the screw 12 within the extruder 10 is suppressed, and the pressure of the molten resin R within the extruder 10 increases.

As described above, by providing the resistance member 51 and the biasing mechanism 54, the molten resin R in the extruder 10 is given resistance to suppress the feeding by the screw 12, so the original feeding speed by the screw 12 , the actual delivery speed of the molten resin R becomes slower than Therefore, the molten resin R is sheared by the blade plate 14 while being pushed toward the die head 22 by the blade plate 14 of the screw 12 . The kneading of the molten resin R proceeds by shearing by the screw 12 .

As a means for shearing the molten resin R, there is a method of concentrating and stirring the molten resin R with a mixer in the middle of delivery for a short period of time. The temperature of R will rise. If the molten resin R is extruded while the temperature is high, the inner peripheral surface of the parison P may not be smooth and uneven. In this regard, in this embodiment, since the melted resin R is slowly sheared in the process of being delivered from the extruder 10, the frictional resistance is kept small, and the melted resin R does not become hot. Therefore, the inner peripheral surface of the parison P is formed as a smooth surface without irregularities.

Table 1 below shows Embodiments 1 to 3 in which a parison P is molded using a blow molding apparatus A equipped with a resistance applying means 50, and a parison P using a molding apparatus (not shown) having no resistance applying means 50. Comparative Examples 1 to 4 are shown. The embodiment and the comparative example were carried out under the following common conditions. The material of the molten resin R is a polyamide resin (thermoplastic resin) containing an impact resistant material (rubber), and the melting point of the molten resin R is 220°C.

The "melt viscosity" in Table 1 is the value of the viscosity of the molten resin R at 250°C and a shear rate of 12/s. In the first to third embodiments in which the resistance member 51 is provided between the delivery port 16 (downstream end of the delivery path) and the upstream end of the inflow passage 26, the "opening ratio" is positioned near the upstream side of the resistance member 51. It is the ratio of the total opening area of the plurality of through holes 52 formed in the resistance member 51 to the cross-sectional area of the delivery port 16 . Comparative Examples 1 to 4, in which the resistance member 51 is not provided, have an aperture ratio of 100%. The “pressure of the molten resin” is the pressure of the molten resin R at the tip of the extruder 10 , inside the storage chamber 25 and inside the die head 22 . The "smoothness of the inner peripheral surface of the parison" indicates the presence or absence of unevenness on the inner peripheral surface of the parison P and the degree of unevenness.

In Embodiment 1, the molten resin R having a melt viscosity of 15,000 [Pa s] is used, the extruder 10 is not provided with a mixer, the compression ratio of the extruder 10 is 3.4, and the resistance applying means 50 is Only the resistance member 51 was used, and the aperture ratio was set to 60%. The compression ratio of the extruder 10 is determined by dividing the depth of the groove 20 of the screw 12 in the feeding section 17 (dimensional difference between the outer diameter of the blade plate 14 and the outer diameter of the shaft section 13) into the groove 20 of the screw 12 in the measuring section 19. is a numerical value divided by the depth of (the dimensional difference between the outer diameter of the blade plate 14 and the outer diameter of the shaft portion 13). As the compression ratio is higher, the shearing action on the molten resin R is improved, so the kneading degree of the molten resin R is also increased.

In Embodiment 2, the molten resin R having a melt viscosity of 21,000 [Pa s] is used, the extruder 10 is not provided with a mixer, the compression ratio of the extruder 10 is 3.4, and the resistance applying means 50 is Only the resistance member 51 was used, and the aperture ratio was set to 60%. In Embodiment 3, the molten resin R having a melt viscosity of 21,000 [Pa s] is used, the extruder 10 is not provided with a mixer, the compression ratio of the extruder 10 is set to 3.4, and the resistance applying means 50 is A resistance member 51 and an urging mechanism 54 are used, and the aperture ratio is set to 47%.

In Comparative Example 1, the molten resin R having a melt viscosity of 3,500 [Pa·s] was used, the extruder 10 was not provided with a mixer, and the compression ratio of the extruder 10 was set to 2.4. In Comparative Example 2, a molten resin R having a melt viscosity of 15,000 [Pa·s] was used, the extruder 10 was not provided with a mixer, and the compression ratio of the extruder 10 was set to 2.4. In Comparative Example 3, a molten resin R having a melt viscosity of 15,000 [Pa·s] was used, the extruder 10 was not provided with a mixer, and the compression ratio of the extruder 10 was set to 3.4. In Comparative Example 4, a molten resin R having a melt viscosity of 15,000 [Pa·s] was used, a mixer was provided in the extruder 10, and the compression ratio of the extruder 10 was set to 2.2.

The parisons P molded under the conditions of Embodiments 1 to 3 and Comparative Examples 1 to 4 will be described. As for drawdown, in Comparative Example 1 with a low melt viscosity (less than 5,000 [Pa·s]), drawdown occurred before the length of the parison P reached 1.8 m. On the other hand, in Embodiments 1 to 3 and Comparative Examples 2 to 4, the melt viscosity is high (because it is 5,000 [Pa s] or more), so even if the length of the parison P is extended to 1.8 m, there is no drawdown. did not occur.

Regarding the smoothness of the inner peripheral surface of the parison P (presence or absence of unevenness and the degree of unevenness), in Comparative Example 1, the compression ratio is low (less than 2.6), and the resistance to the molten resin R in the extruder 10 is low. Since it is not imparted, shearing is insufficient, and there is concern about a decrease in smoothness due to insufficient shearing. However, in Comparative Example 1, since the melt viscosity was low (because it was less than 5,000 [Pa·s]), the smoothness was good. In Comparative Example 2, since the compression ratio was low (less than 2.6) and resistance was not imparted to the molten resin R in the extruder 10, the shear was insufficient and the smoothness was poor. In Comparative Example 3, although the compression ratio was high (2.6 or more), since resistance was not imparted to the molten resin R in the extruder 10, shearing was insufficient and the smoothness was poor. In Comparative Example 4, in addition to heat generation due to rapid shearing in the mixer, the compression ratio was low (less than 2.6) and the shearing during delivery was insufficient, resulting in poor smoothness.

In contrast, in Embodiments 1 to 3 in which the compression ratio was high (2.6 or more) and resistance was imparted to the molten resin R in the extruder 10, the smoothness was good. Here, when comparing Embodiments 1 to 3 and Comparative Example 3, the melt viscosity and the compression ratio are approximately the same, but in Comparative Example 3 in which resistance is not given to the molten resin R being delivered by the extruder 10 While the smoothness was poor, in Embodiments 1 to 3 in which resistance was imparted to the molten resin R being delivered from the extruder 10, good smoothness was obtained. From this, it was found that giving resistance to the molten resin R being delivered from the extruder 10 is a factor in increasing the smoothness.

The mechanism by which the smoothness is improved by applying resistance to the molten resin R being delivered from the extruder 10 can be considered as follows. If resistance is applied to the molten resin R delivered from the extruder 10, the molten resin R is sheared while taking time in the process of delivering the molten resin R. Therefore, the molten resin R is kneaded while suppressing heat generation of the molten resin R. can do. That is, it is presumed that the kneadability, which is a factor for obtaining good smoothness, can be improved while suppressing the heat generation that causes the deterioration of smoothness, so that the smoothness will be good.

In addition, the compressibility of the screw 12 (extruder 10), which is a factor for increasing the smoothness of the parison P, and the resistance member 51 (through hole 52) as a means for applying resistance to the molten resin R being delivered by the extruder 10 With respect to the aperture ratio, the compression ratio is preferably 2.8 to 4.0, the aperture ratio is preferably 35% to 70%, and the aperture ratio is more preferably 40% to 62%. If the open area ratio is less than 35%, the load on the extruder 10 will increase due to excessive resistance applied to the molten resin R, which is not preferable. If the open area ratio is more than 70%, the resistance imparted to the molten resin R becomes too small, making it difficult to eliminate insufficient kneading.

As described above, the blow molding apparatus A of the first embodiment includes the extruder 10 that feeds the molten resin R by the screw 12, and the molten resin R fed from the extruder 10 is pushed downward from the nozzle 27 to form the parison P. and a resistance imparting means 50 that imparts a drag force to the molten resin R in the extruder 10 to suppress its movement in the delivery direction.

The molten resin R sent by the screw 12 in the extruder 10 is sheared by the screw 12 by receiving the resistance of the resistance imparting means 50, so the kneading of the molten resin R proceeds. Since the shearing by the screw 12 is not performed intensively in a short time, but is performed over time while being sent to the die head 22 side, there is little frictional resistance, and there is no possibility that the temperature of the molten resin R becomes high. Therefore, it is possible to mold the parison P having a smooth inner peripheral surface without unevenness.

The resistance imparting means 50 also includes a resistance member 51 formed with a plurality of through holes 52 and arranged between the downstream end of the extruder 10 and the die head 22 . When such a resistance member 51 is used, the molten resin R is restrained from moving in the delivery direction due to flow resistance generated when passing through the plurality of through holes 52 . Since the resistance member 51 has a simple shape, the cost can be suppressed.

Further, the die head 22 includes a storage chamber 25 for storing the molten resin R, and a movable member that is displaced in a direction to increase the volume of the storage chamber 25 as the molten resin R is fed from the extruder 10 to the storage chamber 25. 34 are provided. The resistance applying means 50 includes an urging mechanism 54 that applies an urging force to the movable member 34 in a direction to reduce the volume of the storage chamber 25 . According to this configuration, the molten resin R is restrained from moving in the delivery direction by the biasing force applied from the biasing mechanism 54 to the movable member 34 .

Further, the biasing mechanism 54 is configured to include an extrusion cylinder 36 that drives the movable member 34 in the direction of decreasing the volume of the storage chamber 25 . Since the extrusion cylinder 36 has both the function of driving the movable member 34 and the function of applying resistance to the molten resin R, compared to the case where two single-function type fluid pressure cylinders are provided, the blow molding apparatus A structure can be simplified.

Further, the molten resin R may be a polyamide resin that does not contain an impact resistant material (rubber). The material of the molten resin R is not limited to polyamide resin, and may be ethylene-vinyl alcohol copolymer resin, polyethylene terephthalate resin, polyketone resin, polyphenylene sulfide resin, or the like. In addition, these resin materials may be mixed and contained with an impact resistant material such as rubber, an additive for suppressing drawdown, and a filler such as a filler.

Further, when the molten resin R is a polyamide resin or a polyamide resin composition, in order to avoid the occurrence of drawdown, the melt viscosity at 250 ° C. and a shear rate of 12 / s is 5,000 to 25,000 [Pa · s], more preferably 8,000 to 20,000 [Pa·s], and even more preferably 10,000 to 20,000 [Pa·s]. When the molten resin R is an ethylene-vinyl alcohol copolymer resin or an ethylene-vinyl alcohol copolymer resin composition, the melt viscosity at 210° C. and a shear rate of 12/s should be 5,000 to avoid drawdown. 000 to 20,000 [Pa·s] is preferable, and 6,000 to 15,000 [Pa·s] is more preferable.

<Other Examples>
The present invention is not limited to the embodiments explained by the above description and drawings, and the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiments, the resistance member and the biasing mechanism are used as the resistance applying means. good.
(2) In the above embodiment, the biasing mechanism is provided with a fluid pressure cylinder, but the biasing mechanism may not have a fluid pressure cylinder.
(3) In the above embodiment, the urging force of the urging mechanism is generated by the fluid pressure, but the urging force may be generated by the elasticity of the spring.

A... Blow molding device P... Parison R... Molten resin 10... Extruder 12... Screw 22... Die head 25... Storage chamber 27... Nozzle 34... Movable member 36... Cylinder for extrusion (fluid pressure cylinder)
50... Resistance applying means 51... Resistance member 52... Through hole 54... Biasing mechanism

Claims (3)

An extruder that feeds out the molten resin with a screw,
a die head for forming a parison by extruding the molten resin sent from the extruder downward from a nozzle;
and a resistance applying means for applying a resistance force that suppresses the movement of the molten resin in the extruder in the delivery direction ,
The resistance imparting means comprises a resistance member having a plurality of through holes and disposed between the downstream end of the extruder and the die head,
The extruder has a delivery path in which the screw is arranged, and a delivery port having a smaller diameter than the delivery path,
The die head has an inflow channel connected to the outlet,
A blow molding apparatus , wherein the resistance member is provided between the delivery port and the inflow path . The die head is provided with a storage chamber for storing the molten resin, and a movable member that is displaced in a direction to increase the volume of the storage chamber as the molten resin is fed from the extruder to the storage chamber. cage,
2. A blow molding apparatus according to claim 1, wherein said resistance imparting means comprises an urging mechanism for imparting an urging force to said movable member in a direction to reduce the volume of said storage chamber. 3. A blow molding apparatus according to claim 2 , wherein said biasing mechanism comprises a fluid pressure cylinder for driving said movable member in a direction to reduce the volume of said storage chamber.

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