JP7622687B2 - Manufacturing method of high pressure tank - Google Patents

Description

This disclosure relates to a method for manufacturing a high-pressure tank.

Patent Document 1 discloses a method for manufacturing a high-pressure tank by using a resin impregnation molding die to manufacture a high-pressure tank through RTM (Resin Transfer Molding) molding. In this method, a tank, which is an intermediate product of a high-pressure tank in which a fiber bundle is wound around the outer periphery of a liner, is placed in a die, and resin material is pressurized and filled into the die to impregnate the fiber bundle. Furthermore, a "curing process" is performed in which the impregnated resin material is thermally cured in a thermal curing oven, and a fiber-reinforced resin layer is formed on the outer periphery of the liner.

When resin material is pressurized and filled into a mold to impregnate the fiber bundles, if the pressure of the resin being filled (hereinafter simply referred to as "resin pressure") is greater than the internal pressure of the liner (hereinafter simply referred to as "internal pressure"), there is a risk that the resin pressure will cause the liner to deform. For this reason, in general, in the manufacturing method of high-pressure tanks such as those described above, internal pressure is applied so that the internal pressure exceeds the resin pressure to prevent the liner from collapsing.

JP 2021-84317 A

When manufacturing a high-pressure tank using the above-mentioned RTM molding, there is a problem in that delamination occurs within the fiber-reinforced resin layer after the curing process. This delamination is thought to occur because, during RTM molding, the differential pressure between the internal pressure and the resin pressure acts on the fibers as an expansion force, and this expansion force remains as residual stress. In this state, when the tank is heated during the curing process, the shear strength between the resin and the fibers decreases, and the residual stress exceeds the shear strength.

This disclosure can be realized in the following forms:

According to one embodiment of the present disclosure, there is provided a method for manufacturing a high-pressure tank, which uses a resin impregnation molding die to manufacture a high-pressure tank, and includes the steps of: accommodating, in the resin impregnation molding die, a tank that is an intermediate product of the high-pressure tank, in which a fiber bundle constituting a fiber reinforced resin layer before thermal curing is wound around the outside of a liner; filling, in a state in which an internal pressure of the tank is adjusted by an internal pressure adjustment mechanism to be higher than a resin pressure, which is a pressure of the resin material pressurized and filled into the resin impregnation molding die, the resin material is pressurized and filled into the fiber bundle; detecting, after the filling step, a resin curing start point at which the resin pressure starts to decrease as the resin material cures; and, after detecting the resin curing start point in the detection step, reducing, by the internal pressure adjustment mechanism, the internal pressure of the tank in the tank by the internal pressure adjustment mechanism, such that a differential pressure obtained by subtracting the resin pressure from the internal pressure is a positive value and is equal to or lower than a predetermined value.
According to the manufacturing method of the high-pressure tank of the above embodiment, in the internal pressure reduction step, the internal pressure of the tank is reduced by the internal pressure adjustment mechanism, so that the differential pressure between the internal pressure and the resin pressure can be reduced to a predetermined value or less. If this differential pressure is large, it can cause a part of the fiber-reinforced resin layer of the finished high-pressure tank to peel off. By keeping the differential pressure low in the internal pressure reduction step, the occurrence of such peeling can be reduced.

1 is a cross-sectional view showing a high-pressure tank manufactured by a high-pressure tank manufacturing method according to a first embodiment of the present disclosure. 4 is a flowchart showing each step of a manufacturing method for a high-pressure tank according to the first embodiment of the present disclosure. FIG. 2 is a front cross-sectional view showing a schematic diagram of a resin impregnation molding die. FIG. 2 is a front cross-sectional view showing a schematic diagram of a resin impregnation molding die. 11A and 11B are diagrams for explaining an internal pressure adjustment mechanism. 1 is a flowchart showing detailed steps of an RTM molding process. 13 is a graph showing changes in the internal pressure and resin pressure of the tank after the start of a filling and pressurizing operation of the piston. FIG.

A. First embodiment:
A1. Configuration of high pressure tank 1:
A first embodiment of the present disclosure will be described below with reference to Fig. 1 to Fig. 7. Fig. 1 is a cross-sectional view showing a high-pressure tank 1 manufactured by the high-pressure tank manufacturing method of the first embodiment of the present disclosure. The high-pressure tank 1 includes a liner 20, a fiber-reinforced resin layer 30, a resin layer 40, and two nozzles 91, 92. In this embodiment, the high-pressure tank 1 stores a high-pressure (e.g., 70 MPa) gas (e.g., hydrogen or natural gas) in an internal space 11.

In this embodiment, the high-pressure gas stored in the high-pressure tank 1 is hydrogen. The high-pressure tank 1 is loaded onto a mobile object such as a fuel cell vehicle that is powered by a fuel cell that uses hydrogen as fuel gas. The high-pressure tank 1 may also be installed not only in fuel cell vehicles, but also in mobile objects such as ships and airplanes, or in stationary facilities such as homes and buildings.

The liner 20 has a cylindrical portion and hemispherical dome portions disposed on both ends of the cylindrical portion. The liner 20 is a hollow container having an internal space 11 that is a space for filling the inside with gas. The liner 20 is used as the tank body of the high-pressure tank 1. The liner 20 is formed from a resin that has low gas barrier properties, particularly low hydrogen permeability. Examples of resins that can be used to form the liner 20 include polyamide, ethylene vinyl alcohol, and fully saponified polyvinyl alcohol. In this embodiment, polyamide is used.

The fiber-reinforced resin layer 30 is a layer of fiber-reinforced resin in which fibers are impregnated with a thermosetting resin, and is formed on the outside of the liner 20. The fiber-reinforced resin layer 30 may be formed in contact with the outer surface of the liner 20, or may be formed on the outside of the liner 20 via a release agent. The fiber-reinforced resin layer 30 has a carbon fiber-reinforced resin layer 31 containing carbon fibers and a thermosetting resin, and a glass fiber-reinforced resin layer 35 containing glass fibers and a thermosetting resin. For example, an epoxy resin or an unsaturated polyester resin can be used as the thermosetting resin. In this embodiment, an epoxy resin is used. The curing speed and strength of the epoxy resin are adjusted by a curing accelerator.

The carbon fiber reinforced resin layer 31 is formed to cover the entire outer surface of the liner 20 and parts of the nozzles 91 and 92. The carbon fiber reinforced resin layer 31 is made of carbon fiber reinforced plastics (CFRP) in which carbon fibers are impregnated with a thermosetting resin, and has pressure resistance. The strength (e.g., fracture toughness) of the carbon fiber reinforced resin layer 31 contributes more to the pressure resistance of the high-pressure tank 1 than the strength of the glass fiber reinforced resin layer 35 or the resin layer 40.

The glass fiber reinforced resin layer 35 is formed to cover the outer surface of the carbon fiber reinforced resin layer 31. The glass fiber reinforced resin layer 35 is made of glass fiber reinforced plastics (GFRP) in which glass fibers are impregnated with a thermosetting resin, and has higher impact resistance than the carbon fiber reinforced resin layer 31.

The resin layer 40 is formed on the outer surface of the glass fiber reinforced resin layer 35. The resin layer 40 is made of a thermosetting resin that does not contain fibers. The resin layer 40 is made of the same thermosetting resin as the thermosetting resin used in the glass fiber reinforced resin layer 35.

The nozzles 91, 92 include a first nozzle 91 and a second nozzle 92. The first nozzle 91 has a generally cylindrical shape with a through hole that communicates with the internal space 11 of the liner 20. The first nozzle 91 functions as an opening of the high-pressure tank 1 and also functions as an attachment portion for attaching piping and valves to the high-pressure tank 1. The second nozzle 92 has a generally cylindrical shape without a through hole. The nozzles 91, 92 also function as an attachment portion for attaching the liner 20 to a filament winding device when forming the fiber reinforced resin layer 30. The nozzles 91, 92 can be made of metal such as stainless steel or aluminum.

A2. Manufacturing method of the high pressure tank 1:
Next, a method for manufacturing the high-pressure tank 1 will be described. Fig. 2 is a flowchart showing each step of the method for manufacturing the high-pressure tank 1 according to the first embodiment of the present disclosure. As shown in Fig. 2, the method for manufacturing the high-pressure tank 1 includes a tank preparation step (S100), an RTM (Resin Transfer Molding) molding step (S200), and a curing step (S300), and these steps (S100, S200, S300) are performed in order.

In the tank preparation process (S100), the tank 10 is prepared. Specifically, the tank 10 is prepared by winding a fiber bundle around the outer peripheral surface of the liner 20 with the shaft attached to the nozzles 91, 92, forming a fiber layer on the outer peripheral surface of the liner 20. The "tank" prepared here corresponds to "a tank that is an intermediate product of a high-pressure tank with a fiber bundle wound around the outside of the liner." The fiber bundle constitutes the fiber-reinforced resin layer 30 before thermal curing.

In the RTM molding process (S200), the fiber bundle of the tank 10 is impregnated with a thermosetting resin material (hereinafter simply referred to as "resin") using the RTM method with a resin impregnation molding die, and the impregnated resin is hardened to a certain extent. Details of this RTM molding process (S200) will be described later, along with the configuration of the resin impregnation molding die.

In the curing process (S300), the tank 10 is removed from the resin impregnation molding die and heated in a heat curing furnace (not shown) to completely cure the resin impregnated in the RTM molding process (S200), thereby forming the fiber reinforced resin layer 30 and the resin layer 40. The fiber reinforced resin layer 30 and the resin layer 40 are formed on the outer peripheral surface of the liner 20, completing the high-pressure tank 1.

A3. Configuration of the resin impregnation molding die 50:
Next, the RTM molding step (S200) will be described in detail. First, the configuration of the resin impregnation molding die 50 will be described with reference to Figs. 3 to 5. Figs. 3 and 4 are front cross-sectional views that typically show the resin impregnation molding die 50. Fig. 3 shows the state before the resin material is pressurized by pistons 56, 57, which will be described later, and Fig. 4 shows the state after the resin material is pressurized by pistons 56, 57.

As shown in Figures 3 and 4, the resin impregnation molding die 50 includes an upper die 51 and a lower die 52. An upper storage section 53 and a material flow path 54 are formed in the upper die 51. The upper storage section 53 is formed on the mating surface with the lower die 52, and is formed in approximately the same shape as the upper half of the tank 10 in the radial direction. The material flow path 54 is formed penetrating the upper die 51 in the vertical direction. One end of the material flow path 54 is connected to a resin material supply source (not shown), and the other end is connected to the upper storage section 53.

The lower mold 52 is formed with a lower storage section 55 and holding sections 58 and 59. The lower storage section 55 is formed on the mating surface with the upper mold 51, and is formed in approximately the same shape as the lower half of the tank 10 in the radial direction. Therefore, when the upper mold 51 and the lower mold 52 are clamped together, the upper storage section 53 and the lower storage section 55 are united and connected to form a storage section 60 that is approximately the same shape as the tank 10. The tank 10 is stored in the storage section 60 with its axial direction aligned horizontally.

The holding parts 58, 59 are formed penetrating the lower mold 52 in the vertical direction, and hold the pistons 56, 57 therein so that they can be raised and lowered. The holding parts 58, 59 and the pistons 56, 57 are formed in a generally elliptical shape in a plan view, and are provided generally symmetrically on both radial sides of the tank 10 in a front view. The upper surface of each piston 56, 57 and the inner peripheral surface of each holding part 58, 59 define a material storage section 61. A sealing member (not shown) is provided around the entire outer peripheral surface of each piston 56, 57 to prevent the resin stored in the material storage section 61 from leaking into the space below.

When the mold is closed, the material storage section 61 communicates with the material flow path 54 and is capable of storing the resin material supplied from the material flow path 54. The material storage section 61 communicates with the storage section 60, and when material is stored in the material storage section 61, the storage section 60 is also filled with the resin material.

Furthermore, the upper storage section 53 is provided with a pressure sensor 63. In this embodiment, four pressure sensors 63 are provided at different positions on the inner wall surface of the upper storage section 53. The pressure sensors 63 function as part of the inner wall of the storage section 60, and can detect the pressure of the resin material filled in the storage section 60 (hereinafter also simply referred to as "resin pressure"). In this embodiment, the detection result of the pressure sensor 63 is treated as the pressure (i.e., "resin pressure") of the resin material pressure-fed to the storage section 61 by the pistons 56, 57.

Figure 5 is a diagram for explaining the internal pressure adjustment mechanism 70 that adjusts the internal pressure of the tank 10 during RTM molding. Note that in Figure 5, the tank 10 is illustrated as being similar to the high-pressure tank 1 as a finished product shown in Figure 1, but strictly speaking, when RTM molding begins, the resin has not yet been impregnated and cured, and the fiber-reinforced resin layer 30 and the resin layer 40 are not yet complete.

As shown in FIG. 5, the internal pressure adjustment mechanism 70 includes a supply flow path 71 through which nitrogen gas flows when it is sealed into the internal space 11 of the tank 10 via the first nozzle 91, and a recovery flow path 77 that recovers gas discharged from the tank 10. The internal pressure adjustment mechanism 70 adjusts the pressure inside the liner 20 by pressurizing the tank 10 by sealing in gas (e.g., nitrogen gas) and reducing the pressure by recovering the sealed gas.

A pressure pump 72 that pressurizes gas toward the tank 10 is disposed in the supply flow path 71. An on-off valve 75 is disposed in the supply flow path 71 between the pressure pump 72 and the tank 10. The on-off valve 75 switches the pressure pump 72 side and the tank side of the supply flow path 71 between a non-communicating state and a communicating state.

A pressure reducing pump 78 is disposed in the recovery passage 77 to assist in the recovery of the gas sealed in the liner 20. A pressure adjusting valve 79 is disposed in the recovery passage 77 between the pressure reducing pump 78 and the tank 10. The pressure adjusting valve 79 is a valve mechanism that can adjust the flow path width of the recovery passage 77 in stages. A pressure sensor 81 is disposed in the recovery passage 77 to measure the pressure in the space between the tank 10 and the pressure adjusting valve 79.

The internal pressure adjustment mechanism 70 and the resin impregnation molding die 50 are connected to a control unit 82 that manages a series of controls in the RTM molding process (S200). The control unit 82 is a microcomputer having a central processing unit (CPU) and a storage device (not shown). The storage device is, for example, a RAM, a ROM, or a hard disk drive (HDD). Various programs for implementing the method provided in this embodiment are stored in the HDD or ROM, and the various programs read from the HDD or ROM are deployed on the RAM and executed by the CPU. The detection results of the pressure sensors 63 and 81 described above are stored in the storage device. Pressure information measured by the pressure sensors 63 and 81 is transmitted to the control unit 82.

The control unit 82 adjusts the pressure inside the liner 20 by controlling the pressure pump 72, the on-off valve 75, the pressure regulating valve 79, and the pressure reducing pump 78 in accordance with the received pressure information. In this way, the control unit 82 uses the detection results of each sensor 63, 81 to control the internal pressure adjustment mechanism 70 as well as to control the elevation and lowering of the pistons 56, 57.

A4. Details of the RTM molding process (S200):
Fig. 6 is a flow chart showing the detailed steps of the RTM molding process (S200). As shown in Fig. 6, the RTM molding process (S200) includes a containing process (S201), a resin injection process (S202), a filling process (S203), a detection process (S204), an internal pressure reduction process (S205), and a mold opening process (S206), and these processes (S201, S202, S203, S204, S205, S206) are performed in order.

In the accommodation step (S201), the tank 10 is accommodated in the lower accommodation section 55 of the lower mold 52 with the upper mold 51 open, and the upper mold 51 is clamped. As a result, the tank 10 is accommodated in the accommodation section 60. In the resin injection step (S202), as shown by the arrow A1 in FIG. 3, the resin material is supplied from the material flow path 54 of the resin impregnation molding mold 50 to the material storage section 61.

In the filling step (S203), as shown in FIG. 4, the resin material is filled into the pressurized fiber bundle by pistons 56, 57. The resin material stored in the material storage section 61 is pressurized and filled into the tank 10 at a set resin pressure by the pressing action of pistons 56, 57, as shown by arrow A2 in FIG. 4. At this time, the internal pressure of the tank 10 is adjusted by the internal pressure adjustment mechanism 70 so that it is greater than the resin pressure. This is to prevent the tank 10 from collapsing due to the resin pressure.

Figure 7 is a graph showing the change in the internal pressure and resin pressure of the tank 10 after the start of the filling and pressurizing operation of the pistons 56 and 57. In Figure 7, the change in the internal pressure of the tank 10 is shown by a solid line, and the change in the resin pressure is shown by a dashed line. In Figure 7, the resin pressures detected by the four pressure sensors 63 are shown by four dashed lines. Also, the change in the internal pressure of the tank 10 in a comparative embodiment in which the internal pressure reduction process (S205) of this embodiment is not performed is shown by a two-dot chain line. In this embodiment, the resin pressure is set to 5 MPa. As shown in Figure 7, pressure is applied by the pistons 56 and 57 from time 0 to T1. At time T1, the pistons 56 and 57 are in the state shown in Figure 4. During the period from time 0 to T1, the resin pressure is affected by the pressure applied by the pistons 56 and 57, so it repeatedly rises and falls in a short time. For this reason, the graph of the resin pressure shows a waveform that zigzags finely up and down.

Thereafter, the positions of pistons 56, 57 are maintained, and the resin pressure gradually increases from time T1 to time T2. Then, from time T2 when the resin impregnated in the fibers begins to harden and restrain the fibers, the resin pressure gradually decreases. The point at time T2 when the resin begins to harden is called the "resin hardening start point P." In the detection process (S204), the resin hardening start point P, where the resin pressure begins to decrease as the resin material hardens, is detected. The resin hardening start point P is detected by the control unit 82 through sensing by the pressure sensor 63.

The period from time 0 to T1 corresponds to the filling step (S203), and the period from time T2 to T3 corresponds to the internal pressure reduction step (S205). In the internal pressure reduction step (S205), after the resin hardening start point P is detected, the pressure regulator valve 79 reduces the internal pressure of the tank 10. At this time, the internal pressure is reduced by the internal pressure adjustment mechanism 70 so that the differential pressure D obtained by subtracting the resin pressure from the internal pressure is a positive value and is equal to or less than a predetermined value. A large differential pressure D can cause part of the fiber reinforced resin layer 30 of the finished high-pressure tank 1 to peel off after the curing step (S300). The average pressure value obtained from the multiple pressure sensors 63 can be used as the resin pressure.

Here, the predetermined value is, for example, about 0.5 MPa or about 10% of the resin pressure. The inventors of the present application performed tests by changing the setting of the differential pressure D in various ways to see the extent to which peeling occurs in the high-pressure tank 1 as a finished product. The set temperature of the tank 10 in the curing process (S300) was 110°C, and the time left after reaching the set temperature was 20 minutes. As a result, the effect of suppressing peeling was higher as the differential pressure D was smaller. In general, if the differential pressure D was 0.5 MPa or less, peeling occurred less and product precision was met. Note that the occurrence of peeling varies depending on various setting conditions such as the set temperature and heating time of the work (tank 10) in the curing process (S300) and the type of resin to be impregnated, so it is preferable to perform tests to set the target value of the differential pressure D that can suppress peeling to a level that satisfies the standards of the finished product after various processing conditions have been determined.

By this internal pressure reduction process (S205), the differential pressure D after the resin hardening start point P is maintained at a positive value and below a predetermined value. That is, as shown by the two-dot chain line in FIG. 7, if the internal pressure reduction process (S205) is not performed and the internal pressure control is left to chance, the differential pressure increases as the resin pressure decreases, whereas in this embodiment, the differential pressure D is maintained below a predetermined value. When the internal pressure reduction process (S205) is completed and a predetermined time has elapsed since the start of the material supply, it is determined that the resin has hardened to a certain extent, and the mold opening process (S206) is started. In the mold opening process (S206), the upper mold 51 is removed and the tank 10 is taken out of the storage section 60. After that, the above-mentioned curing process (S300) is performed.

According to the manufacturing method of the high-pressure tank 1 of the first embodiment described above, in the internal pressure reduction step (S205), after the resin hardening start point P is detected in the detection step (S204), the internal pressure of the tank 10 is reduced by the internal pressure adjustment mechanism 70, so that the differential pressure D between the internal pressure and the resin pressure is adjusted to a predetermined value or less. If this differential pressure D is large, it can cause part of the fiber-reinforced resin layer 30 of the high-pressure tank 1 as a finished product to peel off.

More specifically, the peeling of the fiber-reinforced resin layer 30 that occurs after the curing step (S300) is caused by the pressure difference D between the internal pressure and the resin pressure acting as an expansion force on the fibers during the RTM molding (S200), which becomes a residual stress, and in this state, when the tank 10 is heated during the curing step (S300), the shear strength between the resin and the fibers decreases, and the residual stress exceeds the shear strength. In the above embodiment, by keeping the pressure difference D between the internal pressure and the resin pressure during the RTM molding step (S200), which causes peeling, low, the residual stress is prevented from exceeding the shear strength, and as a result, the occurrence of such peeling can be reduced.

In addition, since the internal pressure is only reduced at a predetermined time after the resin hardening start point P is detected, there is no need for complex control throughout the entire RTM molding process (S200).

B. Other embodiments:
(B1) The resin impregnation molding die 50 for implementing the manufacturing method of the high-pressure tank 1 of the first embodiment has the pistons 56, 57, and the filling and pressurizing of the resin is performed by the pistons 56, 57, but this does not have to be the case. In addition, the shape of each of the pistons 56, 57 is not limited to a circular shape in a plan view. The shape of each of the pistons 56, 57 may be, for example, a substantially rectangular shape with arc-shaped corners in a plan view.

(B2) In the manufacturing method of the high-pressure tank 1 of the first embodiment, the resin pressure is detected from multiple (four) pressure sensors 63, but the number of pressure sensors 63 is not limited to four and may be one, or any multiple other than four. The pressure sensor 63 may be provided on the inner wall surface of the lower storage section 55 instead of the inner wall surface of the upper storage section 53. The pressure sensor 63 is not limited to the storage section 60, and may be disposed at any position in the internal space of the mold 50, such as the material flow path 54 or the material storage section 61. The pressure sensor 63 may be omitted, for example, when the pressurizing mechanism is provided with a sensor for detecting the pressure of the resin material pumped by the pistons 56 and 57 that constitute the pressurizing mechanism.

(B3) In the manufacturing method of the high-pressure tank 1 of the first embodiment described above, in the RTM molding process (S200), the internal pressure is maintained at approximately the same value after time T2, but it is sufficient that the differential pressure D is maintained at or below a predetermined value for a period exceeding a predetermined time (e.g., at least about 60 seconds) that is thought to affect the occurrence of peeling, and thereafter, it may be gradually reduced to a level that does not fall below the resin pressure.

The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit of the disclosure. For example, the technical features in each embodiment corresponding to the technical features in each form described in the Summary of the Invention column can be replaced or combined as appropriate to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described in this specification as essential, it can be deleted as appropriate.

1...High pressure tank, 10...Tank, 11...Internal space, 20...Liner, 30...Fiber reinforced resin layer, 31...Carbon fiber reinforced resin layer, 35...Glass fiber reinforced resin layer, 40...Resin layer, 50...Resin impregnation molding die, 51...Upper die, 52...Lower die, 53...Upper storage section, 54...Material flow path, 55...Lower storage section, 56, 57...Piston, 58, 59...Holding section, 60...Storage section, 61...Material storage section, 63...Pressure sensor, 70...Internal pressure adjustment mechanism, 71...Supply flow path, 72...Pressure pump, 75...Opening and closing valve, 77...Recovery flow path, 78...Decompression pump, 79...Pressure adjustment valve, 81...Pressure sensor, 82...Control section, 91...First nozzle, 92...Second nozzle

Claims (1)

A method for manufacturing a high-pressure tank using a resin impregnation molding die, comprising the steps of:
A process of placing a tank, which is an intermediate product of the high-pressure tank in which the fiber bundle constituting the fiber reinforced resin layer before thermal curing is wound around the outside of the liner, in the resin impregnation molding die;
a filling step of pressurizing and filling the resin material into the resin impregnation molding die to fill the fiber bundle while adjusting the internal pressure of the tank by an internal pressure adjustment mechanism so as to be greater than a resin pressure, which is a pressure of the resin material pressurized and filled into the resin impregnation molding die;
a detection step of detecting a resin hardening start point at which the resin pressure starts to decrease as the resin material hardens after the filling step;
an internal pressure reducing step of reducing the internal pressure of the tank by the internal pressure adjusting mechanism after detecting the resin hardening start point in the detection step, so that a differential pressure obtained by subtracting the resin pressure from the internal pressure is a positive value and is equal to or less than a predetermined value;
A method for manufacturing a high-pressure tank having the above structure.

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