Fiber-reinforced pressure vessel and method for producing the same

Abstract

To provide a fiber-reinforced pressure vessel which is light in weight while exhibiting excellent rupture strength in a burst test.SOLUTION: A fiber-reinforced pressure vessel comprises a liner having airtightness and a fiber-reinforced resin layer, in which a reinforcing fiber is a carbon fiber, and the fiber-reinforced resin layer has at least: a hoop layer having a fiber winding angle of 85 degrees or more relative to an axis of the liner, a high-angle helical layer having a fiber winding angle of 75 degrees or more and less than 85 degrees, and a low-angle helical layer having a fiber winding angle of less than 30 degrees. A thickness proportion of the hoop layer within the fiber-reinforced resin layer is 15 to 70%, a thickness proportion of the low-angle helical layer is 20 to 70%, and a thickness proportion of the high-angle helical layer is 0.5 to 10%. Preferably, the hoop layer is arranged to sandwich a helical layer, the hoop layer is arranged as both an innermost layer and an outermost layer, the liner is made of a synthetic resin or aluminum alloy, and a resin used in the fiber-reinforced resin layer is a thermosetting resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced pressure vessel for storing high-pressure gas or the like, and more particularly to a fiber-reinforced pressure vessel in which an airtight liner is reinforced with a fiber-reinforced resin layer. [Background technology]

[0002] Fiber-reinforced pressure vessels, which have a metal or resin liner wrapped with resin-impregnated fibers, are widely used as containers for filling high-pressure gases, liquefied gases, etc., because they are extremely light compared to steel containers of the same size and are easy to handle.

[0003] In such fiber-reinforced pressure vessels, the liner primarily functions as a component that provides airtightness by preventing the permeation of gases, etc., and the resin-impregnated fiber layer primarily functions as a component that provides the strength to withstand high internal pressures. Therefore, when designing a fiber-reinforced pressure vessel to withstand high internal pressures, the configuration of the resin-impregnated fiber layer is extremely important.

[0004] For example, Patent Document 1 discloses a tank having a hoop layer and a helical layer as reinforcing fiber layers, and the elastic modulus of the impregnated resin in the helical layer is greater than that of the hoop layer. Patent Document 2 also proposes a high-pressure gas storage container having three types of stacking angles for the fiber-reinforced resin layer: a helical angle of 0 to 20°, a hoop angle of 80 to 90°, and a stacking angle of 20 to 80°.

[0005] However, these structures still have the problem of not being able to achieve a stable high burst strength in burst tests. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-32088 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-176898 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above background, and an object of the present invention is to provide a fiber-reinforced pressure vessel which is lightweight yet has excellent burst strength in a burst test. [Means for solving the problem]

[0008] The fiber-reinforced pressure vessel of the present invention is a fiber-reinforced pressure vessel consisting of an airtight liner and a fiber-reinforced resin layer, in which the reinforcing fibers are carbon fibers, and the fiber-reinforced resin layer has at least the following layers: a hoop layer in which the winding angle of the fibers relative to the axis of the liner is 85 degrees or more, a high-angle helical layer in which the winding angle is 75 degrees or more but less than 85 degrees, and a low-angle helical layer in which the winding angle is less than 30 degrees; and the thickness ratio of the hoop layer in the fiber-reinforced resin layer is 15 to 70%, the thickness ratio of the low-angle helical layer is 20 to 70%, and the thickness ratio of the high-angle helical layer is in the range of 0.5 to 10%.

[0009] It is also preferable that the fiber-reinforced resin layer further includes a high-angle helical layer in which the winding angle of the fibers relative to the axis of the liner is 60 degrees or more but less than 75 degrees, or a medium-angle helical layer in which the winding angle of the fibers relative to the axis of the liner is 30 degrees or more but less than 60 degrees.

[0010] Furthermore, it is preferable that the total thickness ratio of the hoop layer and the high-angle helical layer in the fiber-reinforced resin layer is in the range of 16 to 48%, that it has a high-angle helical layer of 60 degrees or more but less than 75 degrees, and that its thickness ratio is in the range of 1 to 20%, and that it has a medium-angle helical layer of 30 degrees or more but less than 60 degrees, and that its thickness ratio is in the range of 1 to 20%.

[0011] It is also preferable that the hoop layers are arranged with the helical layer sandwiched between them, that the hoop layers are arranged as the innermost and outermost layers, that the liner is made of synthetic resin or aluminum alloy, and that the resin used in the fiber-reinforced resin layer is a thermosetting resin.

[0012] Another method for manufacturing a fiber-reinforced pressure vessel of the present invention is characterized in that, when winding a carbon fiber bundle impregnated with resin onto the surface of an airtight liner, at least a hoop layer having a fiber winding angle relative to the axis of the liner of 85 degrees or more, a high-angle helical layer having a winding angle of 75 degrees or more but less than 85 degrees, and a low-angle helical layer having a winding angle of less than 30 degrees, with the thickness ratio of the hoop layer being in the range of 15 to 70%, the thickness ratio of the low-angle helical layer being in the range of 20 to 70%, and the thickness ratio of the high-angle helical layer being in the range of 0.5 to 10%. [Effects of the Invention]

[0013] According to the present invention, a fiber-reinforced pressure vessel is provided which is lightweight yet has excellent burst strength in a burst test. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing a schematic structure of a fiber-reinforced pressure vessel of the present invention. [Figure 2] FIG. 1 is a conceptual diagram of hoop winding in a fiber-reinforced pressure vessel. [Figure 3] 1 is a conceptual diagram of high-angle helical winding in a fiber-reinforced pressure vessel. [Figure 4] 1 is a conceptual diagram of low-angle helical winding in a fiber-reinforced pressure vessel. [Figure 5] This is a conceptual diagram showing the difference in the reinforcing effect on the mirror part (dome part) depending on the angle of the helical winding. [Figure 6] 10 is a graph showing heat treatment conditions after a fiber reinforced resin material is wound around a liner. DETAILED DESCRIPTION OF THE INVENTION

[0015] The fiber-reinforced pressure vessel of the present invention is a fiber-reinforced pressure vessel consisting of an airtight liner and a fiber-reinforced resin layer, in which the reinforcing fibers are carbon fibers, and is characterized in that the fiber-reinforced resin layer has at least each of the following layers, each having a fiber winding angle relative to the liner axis of "a hoop layer of 85 degrees or more," "a high-angle helical layer of 75 degrees or more but less than 85 degrees," and "a low-angle helical layer of less than 30 degrees." Furthermore, it is essential that the thickness ratio of the hoop layer in the fiber-reinforced resin layer is 15 to 70%, the low-angle helical layer is 20 to 70%, and the high-angle helical layer is 0.5 to 10%.

[0016] Here, the winding angle of the fibers in each layer is the angle when the hoop winding, which is wound almost perpendicular to the tank axis of the container in the body of the container, is "85 degrees or more" (winding perpendicular to the tank axis is "90 degrees"; "α1" in Figure 2), and winding parallel to the tank axis is "0 degrees." For example, the angle of various helical windings corresponds to the angle "α2" in Figure 3. Also, in order to level out the fiber reinforcement, each angle is normally used as a pair of two directions, "+ (plus)" and "- (minus)," and the thickness percentages shown above are the total amount of layers with the corresponding angle in the fiber-reinforced resin layer.

[0017] As long as the thickness ratios of each layer are satisfied, it is also preferable to have a "high-angle helical layer of 60 degrees or more and less than 75 degrees" and / or a "medium-angle helical layer of 30 degrees or more and less than 60 degrees" in addition to the above, depending on the desired physical properties. Furthermore, other fibers such as glass fiber may be added to the fiber-reinforced resin layer in addition to carbon fiber, and it is particularly preferable to place a fiber-reinforced resin layer made of glass fiber in the outermost layer, which allows the glass fiber-reinforced resin layer to prevent surface damage that is likely to occur when the container is used and protect the carbon fiber-reinforced resin layer.

[0018] The fiber-reinforced pressure vessel of the present invention preferably has "0.5 to 10%" of "high-angle helical layers with an angle of 75 degrees or more but less than 85 degrees," with 1 to 8%, and especially 1.5 to 5% being preferred. Furthermore, "hoop layers of 85 degrees or more" preferably have "15 to 70%," with 24 to 42%, and especially 30 to 40% being preferred. The combined high-angle helical layers and hoop layers preferably account for 16 to 48% of the total, with the total preferably being 25 to 45%.

[0019] Furthermore, in the fiber-reinforced pressure vessel of the present invention, the "low-angle helical layer of less than 30 degrees" must be in the range of "20 to 70%, more preferably 40 to 60%, and particularly preferably 45 to 55%.

[0020] Furthermore, if there is a "high-angle helical layer of 60 degrees or more and less than 75 degrees" other than those mentioned above, it is preferable that the high-angle helical layer is in the range of 1 to 20%. If there is a "medium-angle helical layer of 30 degrees or more and less than 60 degrees", it is preferable that the medium-angle helical layer is in the range of 1 to 20%.

[0021] The thickness ratio of each layer is the total of multiple layers, and it is preferable that even the same "hoop layer" is arranged discontinuously rather than continuously.

[0022] Furthermore, it is preferable that the innermost layer, including the first layer in contact with the liner, be a hoop layer. It is also preferable to place a hoop layer on the outermost layer, as this facilitates suppressing the generation of voids and sagging of the fiber bundles in the helical layer. In the body of a pressure vessel loaded with internal pressure, the stress generated in the circumferential direction of the vessel is theoretically approximately twice the stress generated in the axial direction of the vessel. Therefore, the placement of a hoop layer is important for increasing the burst strength in burst tests and meeting the standard values. On the other hand, as mentioned above, focusing only on reinforcing the body makes the dome portion more susceptible to fracture and damage, so the placement of a helical layer is also important for reinforcing the dome portion.

[0023] Furthermore, it is preferable that the "hoop layers" be arranged so that the end positions of the overlapping windings are closer to the center of the cylindrical body for each layer. This reduces the step height at both ends of the hoop layer, making it possible to further reduce the bending of the helically wound fiber bundle that is wound over the hoop winding.

[0024] Regarding the "helical layer," it is preferable that the folded positions in the overlapping head section are not consecutively wound with the same folded diameter, but that each layer is shifted by at least half the fiber bundle width. This prevents distortion of the carbon fiber reinforced resin lamination in the head section and reduces the number of locations where excessive stress is concentrated.

[0025] In the fiber-reinforced pressure vessel of the present invention, by setting the maximum angle helical layer and other layer configurations within the above ranges, the rupture strength of the fiber-reinforced pressure vessel during a burst test can be increased, and the main rupture site can be located in the barrel portion rather than the head portion (dome portion). Generally, pressure vessels with this type of structure have a larger variation in strength in the head portion than in the barrel portion, and a pressure vessel that stably ruptures in the barrel portion during a burst test is considered to be a more reliable pressure vessel with less variation. The configuration of the present invention is also effective in ensuring that the rupture site is located in the barrel portion rather than the head portion.

[0026] The carbon fibers used in the fiber-reinforced resin layer preferably have a tensile modulus of 200 GPa or more, particularly preferably in the range of 235 to 600 GPa.The tensile strength of the carbon fibers is preferably 3000 MPa or more, more preferably in the range of 4000 to 8000 MPa, and even more preferably in the range of 5000 to 7000 MPa.

[0027] The carbon fiber used as such reinforcing fiber is preferably a fiber bundle composed of a large number of filaments, and is preferably 2,000 (2K) or more, more preferably 4,000 (4K) to 40,000 (40K), and particularly preferably in the range of 8,000 (8K) to 32,000 (32K). By using such fiber bundle reinforcing fiber, it becomes possible to efficiently wind a large number of reinforcing fibers on the liner.

[0028] There are no particular restrictions on the airtight liner used in the fiber-reinforced pressure vessel of the present invention, but to make the pressure vessel lightweight, aluminum alloys, resin materials, non-metallic elastic materials, etc. are preferred. Thermoplastic resins that are impermeable to the enclosed fluid are preferably used as the raw resin for forming the liner. Nylon resin is particularly preferred, but other resins such as polypropylene resin, polyethylene resin, and ethylene-vinyl alcohol copolymer resin can also be used.

[0029] Further, preferred embodiments of the fiber-reinforced pressure vessel of the present invention will be described with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals. The present invention is not limited to the following drawings.

[0030] First, with reference to FIG. 1, the structure of a fiber-reinforced pressure vessel (hereinafter sometimes referred to as an "FRP pressure vessel" or "pressure vessel") of the present invention will be described.

[0031] Pressure vessel 200 has an elongated cylindrical shape overall. Figure 1 is a cross-sectional view of pressure vessel 200 cut along a plane including the central axis of the cylinder. Pressure vessel 200 comprises a cylindrical body 201, a dome-shaped bottom 202, and a dome-shaped head 203 (the bottom and head together may be referred to as the "head portion" or "dome portion").

[0032] The body 201 is a cylindrical portion of the pressure vessel 200 having approximately constant outer dimensions. The bottom 202 is a portion provided at the bottom of the pressure vessel 200 and is a portion provided at one end of the body 201. A plug member 205 may be provided at the center of the bottom 202. The head 203 is a portion provided at the top of the pressure vessel 200 and is a portion provided at the other end of the body 201 opposite the bottom. The head 203 is provided with a mouthpiece 206. When forming a reinforcing layer on the outer surface of the liner, it is necessary to fix both ends of the liner and rotate the liner around an axis connecting both ends of the liner. The top of the liner is fixed by the mouthpiece 206, and the bottom of the liner is fixed by a jig. The plug member 205 is the remaining portion after the jig is cut.

[0033] The pressure vessel 200 also includes a storage space 204 therein for storing a gas or liquid. The storage space 204 is typically filled with a gas, and the gas is typically filled with a pressure higher than normal pressure. For example, when the pressure vessel 200 is used in a fuel cell system, a fuel gas, typically hydrogen, is filled into the storage space 204 under high pressure, and this fuel gas is decompressed and used to generate electricity in the fuel cell.

[0034] The nozzle 206 is a component to which the valve assembly 250 or piping (not shown) is connected. The nozzle 206 is provided at the center of the hemispherical end wall of the pressure vessel 200. The nozzle 206 is made of a metal such as an aluminum alloy or stainless steel. A female thread (not shown) is formed on the inner circumferential surface of an opening 207 provided in the nozzle 206. The valve assembly 250 or piping can be screwed into the nozzle 206 via the female thread.

[0035] For example, when the pressure vessel 200 is used in a fuel cell system, the storage space 204 is connected to an external gas flow path (not shown) via a valve assembly 250 in which piping elements such as valves and joints are integrally assembled. This allows hydrogen to be filled into the storage space 204 from the outside, and hydrogen to be released from the storage space 204 to the outside. The nozzle 206 may be provided not only on the head 203 but also on the bottom 202.

[0036] The pressure vessel 200 also includes a fiber-reinforced resin layer 220 (hereinafter sometimes referred to as a "reinforcement layer") on the surface of the liner 210. The liner 210 is disposed inside the pressure vessel 200 and is a member that hermetically contains gas or liquid. The liner 210 includes a liner body 211 that corresponds to the body 201, a liner bottom 212 that corresponds to the bottom 202, and a liner head 213 that corresponds to the head 203.

[0037] The liner 210 has the function of suppressing the permeation of gas or liquid stored in the storage space 204 and suppressing the contact of the gas or liquid with the reinforcing layer 220. The liner 210 is made of a material that has the ability to suppress the permeation of gas or liquid, that is, has excellent gas or liquid barrier properties. The liner 210 can be made of an aluminum alloy, a resin material, a non-metallic elastic material, or the like.

[0038] Furthermore, in a preferred embodiment of the present invention, the liner 210 is made of resin. The resin used to manufacture the liner 210 is preferably nylon resin, which has excellent impact resistance, durability, chemical resistance, and flexibility.

[0039] Furthermore, the manufacturing process of the liner 210 will be described in detail. Generally, when it comes to manufacturing liners made of resin, injection molding, blow molding, rotational molding, etc. are known. Also, there are liners that are integrally molded as a whole, and liners that are made by welding together multiple prefabricated resin molded parts. For example, the latter is made by joining the edges of bowl-shaped side liner sections to both ends of a cylindrical center liner section by infrared welding, heat welding, etc.

[0040] An example of a preferred manufacturing method when the liner is made of an aluminum alloy is shown below: The aluminum alloy used to manufacture the liner 210 is preferably an A6000 series aluminum alloy.

[0041] First, in step 1, an aluminum alloy plate is prepared and loaded into a machine tool. The aluminum alloy plate is preferably a disk-shaped plate made of an aluminum alloy. Then, in step 2, the aluminum alloy plate is subjected to press cupping. In step 2, a bottom 202, which is a dome-shaped portion at the bottom of the pressure vessel 200, is formed. Next, in step 3, the cup-shaped aluminum alloy that has been press cupped is subjected to forming, also known as stretching. In step 3, a body 201, which is a cylindrical portion in the center of the pressure vessel 200, is formed. The shape of the processed product in step 3 is similar to that of a test tube used in chemical experiments, etc., with one end open.

[0042] Then, in step 4, a spinning process is performed on the opening of the aluminum alloy, which is roughly test tube shaped and has been machined in steps 1 to 3. In step 4, a head 203, which is the dome-shaped portion at the top of the pressure vessel 200, is formed. In steps 2 to 4, the pressure vessel 200 is roughly finished into the vessel shape. In step 5, a heat treatment is performed. In step 6, a thread cutting process is performed on the pressure vessel 200. In step 6, the nozzle 206 is threaded and shaped by machining. By performing steps 1 to 6, the liner 210 is completed.

[0043] The fiber-reinforced pressure vessel of the present invention has a structure in which a fiber-reinforced resin layer is wound around the resin or aluminum alloy liner as described above. The fibers in the fiber-reinforced resin layer used in the present invention include carbon fibers, and constitute a so-called CFRP (carbon fiber reinforced plastic) reinforcing layer.

[0044] The matrix resin used in such a fiber-reinforced resin layer is preferably a thermosetting resin, more preferably an epoxy resin. Other possible matrix resins include phenolic resins, vinyl ester resins, and unsaturated polyester resins. One matrix resin may be used alone, or two or more may be used in combination.

[0045] Furthermore, the volume content of the matrix resin in the carbon fiber reinforced resin is preferably 25% or more and 45% or less to prevent a decrease in strength. (Although this depends on the specific gravity of the matrix resin, as a guideline, this corresponds to a mass content of the resin ranging from just under 20% to approximately 35%.) 29% or more and 35% or less is more preferable. (Although this also depends on the specific gravity of the matrix resin, as a guideline, this corresponds to a mass content of the resin ranging from just over 20% to just under 30%.) Impregnating the resin at a volume content above the lower limit helps to suppress the generation of fiber fluff and voids between fiber bundles during processing. Impregnating the resin at a volume content below the upper limit helps to suppress slippage of the fiber bundles and resin sagging during winding.

[0046] In other words, the reinforcing layer 220, which is such a fiber-reinforced resin layer, mainly compensates for the strength deficiencies of the liner 210 alone and increases the strength of the pressure vessel 200. The reinforcing layer 220 of the present invention is made of FRP (Fiber Reinforced Plastics), which is a fiber-reinforced resin. The fiber-reinforced resin is preferably a carbon-fiber-reinforced resin containing, for example, epoxy resin or phenolic resin and carbon fiber. In addition to such so-called CFRP (Carbon Fiber Reinforced Plastics), it is also possible to use GFRP (Glass Fiber Reinforced Plastics), which is a fiber-reinforced resin containing, for example, epoxy resin or phenolic resin and glass fiber. For example, in a particularly preferred embodiment of the present invention, the pressure vessel is one in which a reinforcing layer 220 is formed by laminating a layer of CFRP and a layer of GFRP in that order around the outer periphery of the liner 210, with the outermost layer being a layer of GFRP.

[0047] Such a fiber-reinforced pressure vessel of the present invention can be obtained by another method for manufacturing a fiber-reinforced pressure vessel of the present invention.

[0048] That is, when a carbon fiber bundle impregnated with resin is wound around the surface of an airtight liner, at least the following layers are formed: a hoop layer with a winding angle of the fiber relative to the axis of the liner of 85 degrees or more, a high-angle helical layer with a winding angle of 75 degrees or more but less than 85 degrees, and a low-angle helical layer with a winding angle of less than 30 degrees; and the thickness ratio of the hoop layer is 15 to 70%, the thickness ratio of the low-angle helical layer is 20 to 70%, and the thickness ratio of the high-angle helical layer is 0.5 to 10%.

[0049] Here, it is preferable that the end position of the hoop winding be closer to the center of the cylindrical body for each layer, as this reduces the height difference at both ends of the hoop winding and reduces bending of the helically wound fiber bundle wound over the hoop winding.

[0050] When helically winding, it is preferable not to continuously wind and overlap with the same turn diameter at the head section, and it is more preferable to shift the turn diameter by at least half the fiber bundle width. This prevents distortion of the laminated shape of the carbon fiber reinforced resin at the head section and reduces the number of places where stress is concentrated.

[0051] It is also preferable to wind the first layer as a hoop layer, which enables more stable, less variable, high burst strength and burst behavior at the center of the cylindrical body in burst tests.Furthermore, it is also preferable to place a hoop layer on the outermost layer, which makes it possible to better suppress the occurrence of voids in the helical layer and the occurrence of sagging of the fiber bundle.

[0052] An example of the process for forming the reinforcing layer 220 will be further described below. In a preferred embodiment of the present invention, the reinforcing layer 220 is formed around the outer periphery of the liner 210 by filament winding molding. In filament winding molding, for example, carbon fiber pre-impregnated with a thermosetting resin such as epoxy resin, or in some cases reinforcing fiber such as glass fiber, is wound around the outer periphery of the liner 210, and the thermosetting resin is thermally cured to form the reinforcing layer 220.

[0053] Furthermore, when winding the carbon fiber reinforced resin around the liner in the filament winding process (FW process), it is preferable to apply pressure to the inside of the liner. The internal pressure applied to the inside of the liner is preferably in the range of 0.1 MPa or more and 0.5 MPa or less. Applying an appropriate internal pressure makes it possible to suppress dents and deformation of the liner during the FW process.

[0054] Furthermore, in the FW process, the tension applied to the carbon fiber wound around the liner is preferably between 2N and 20N per fiber bundle. Applying tension can prevent the fiber bundle from sagging. However, applying too much tension tends to cause problems such as fuzzing and thread breakage.

[0055] The winding speed of the carbon fiber reinforced resin around the liner is preferably 10 m / min to 20 m / min for hoop winding, 7 m / min to 15 m / min for high-angle helical winding, and 4 m / min to 10 m / min for low-angle helical winding. To improve productivity, a winding speed above the lower limit is preferable, but winding at a speed above the upper limit tends to cause slippage of the fiber bundle and resin scattering, particularly when the helical winding angle is low. However, if improvements and ingenuity can be found to solve the problems of preventing fiber bundle slippage and resin scattering, winding at a speed above the upper limit is possible, leading to further improvements in productivity and therefore acceptable.

[0056] The matrix resin used in the carbon fiber reinforced resin is preferably a thermosetting resin, more preferably an epoxy resin. Other possible matrix resins include phenolic resins, vinyl ester resins, and unsaturated polyester resins. One matrix resin may be used alone, or two or more may be used in combination.

[0057] The volume content of the matrix resin in the carbon fiber reinforced resin is preferably 25% or more and 45% or less to prevent a decrease in strength. (Although this depends on the specific gravity of the matrix resin, as a guideline, this corresponds to a mass content of the resin ranging from just under 20% to approximately 35%.) 29% or more and 35% or less is more preferable. (Although this also depends on the specific gravity of the matrix resin, as a guideline, this corresponds to a mass content of the resin ranging from just over 20% to just under 30%.) Impregnating the resin at a volume content above the lower limit helps to suppress the generation of fiber fluff and voids between fiber bundles during processing. Impregnating the resin at a volume content below the upper limit helps to suppress slippage of the fiber bundles and resin sagging during winding.

[0058] As described above, methods for winding reinforcing fibers such as carbon fiber and glass fiber include hoop winding and various helical windings. In one example of the most preferred embodiment of the present invention, a fiber wound layer of carbon fiber reinforced resin is laminated on the outer periphery of the liner 210, and then a fiber wound layer of glass fiber reinforced resin is laminated as the outermost layer to form the reinforcing layer 220. In the embodiment of the present invention, it is essential to first laminate multiple fiber wound layers with different carbon fiber winding methods on the outer periphery of the liner 210. However, it is also preferable to subsequently laminate multiple fiber wound layers of glass fiber or the like with different winding methods on the fiber wound layer of carbon fiber reinforced resin formed on the outer periphery of the liner 210, as necessary.

[0059] As shown in FIG. 2, hoop winding is a method of winding reinforcing fibers 221, such as carbon fibers or glass fibers, around a cylindrical liner 210 at a winding angle substantially perpendicular to the central axis AX while moving the winding position in a direction along the central axis AX. The winding angle is the angle between the winding direction of the reinforcing fibers 221 and the extension direction of the reinforcing fibers 221. The winding direction of the reinforcing fibers 221 is the movement direction of a reel (not shown) around which the reinforcing fibers 221 are wound, which is the extension direction of the central axis AX. The winding angle α1 of the hoop winding is 85 to 90 degrees, and the fiber winding layer formed by the hoop winding is the hoop layer. Because it is difficult to wind the reinforcing fibers 221 around the liner bottom portion 212 and the liner head portion 213 by hoop winding, the hoop layer is basically formed over the entire liner barrel portion 211. In other words, the hoop layer is important for improving the strength of the body of the pressure vessel 200 in the circumferential direction.

[0060] As shown in FIG. 3 , helical winding involves spirally winding the reinforcing fiber 221 around the liner 210 while maintaining a constant winding angle, switching the winding direction at the end of the liner 210, and then spirally winding the reinforcing fiber 221 around the liner 210 again while maintaining a constant winding angle. In helical winding, the winding direction is switched multiple times, resulting in a fiber-wound layer on the outer surface of the pressure vessel 200 in which the reinforcing fiber 221 is spread across the entire surface in a mesh-like pattern. In the present invention, helically wound layers are classified into four types: "low-angle helical layer (less than 30 degrees)," "medium-angle helical layer (30 degrees to less than 60 degrees)," "high-angle helical layer (60 degrees to less than 75 degrees)," and "high-angle helical layer (75 degrees to less than 85 degrees)." In the present invention, it is particularly important to have a "high-angle helical layer (75 degrees to less than 85 degrees)."

[0061] 3 shows how the reinforcing fiber 221 is wound around the liner 210 using high-angle helical winding. α2, which represents the winding angle of the high-angle helical winding, is a relatively large winding angle that allows the reinforcing fiber 221 to make at least one full turn around the liner body portion 211. While a winding angle of approximately 30 degrees or more and less than 75 degrees is generally used as a guide for the angle of α2, in the present invention, the presence of a "low-angle helical layer less than 30 degrees" and a "high-angle helical layer of 75 degrees or more and less than 85 degrees" is particularly important.

[0062] In "high-angle helical layers," "high-angle helical layers," and "hoop layers" with a winding angle of 60 degrees or more, the winding angle is relatively large enough to allow the reinforcing fiber 221 to make at least one full turn in the liner barrel portion 211. Conversely, in "low-angle helical layers of less than 30 degrees" such as in Figure 4, the winding angle is relatively small enough (angle α3 in Figure 4) that the winding direction is changed before the reinforcing fiber 221 makes one full turn in the liner barrel portion 211. The winding angle is sometimes called the orientation angle.

[0063] Incidentally, the effect of improving the strength of the mirror portion varies depending on the angle of the helical winding. Figures 5(A) and (B) are schematic diagrams illustrating the improvement in the mirror strength due to helical winding. Figures 5(A) and (B) each show the mirror when viewed along the central axis AX. The mirror in Figure 5(A) has a high-angle helical winding, while the mirror in Figure 5(B) has a low-angle helical winding.

[0064] The curved surface of the head portion of the tank container is composed of a constant tension curved surface. In this case, if the folding position of the carbon fiber on the head portion is determined so that the following formula (1) holds, the stress of the carbon fiber on the head portion can be made approximately uniform. R1=R0·sinα0·(1)

[0065] Here, R0 is the radius of the cylinder, and α0 is the winding angle of the carbon fiber around the cylinder. R1 is the distance from the center of the head (central axis AX) to the folding position of the carbon fiber. Specifically, the "folding position of the carbon fiber" refers to the apex position of the curve drawn by the carbon fiber on the head. If the winding direction of the carbon fiber around the head is repeatedly folded back so that the above formula (1) holds, the folding position of the carbon fiber will be located on the circumference of a circle with radius R1 on the head.

[0066] If the folding position of the carbon fiber is set at a position that is different from the above formula (1), for example, if the position is shifted toward the cylinder, the tension of the carbon fiber at the folding position will cause it to shift toward the cylinder during FW molding, or if the position is shifted toward the spinneret, the tension of the carbon fiber at the folding position will cause it to shift toward the spinneret during FW molding, which could result in molding defects and potential fracture initiation points. Therefore, this "folding position of the carbon fiber" is extremely important in improving and stabilizing the strength of the molding surface of the head part.

[0067] Generally, strain on the dome-shaped head portion tends to increase in the direction perpendicular to the fiber direction of the wound carbon fiber. Therefore, in high-pressure gas tanks manufactured using the FW (filament winding) method, the strength of the head portion, which has multiple folding positions, is more likely to decrease than that of the cylinder portion.

[0068] In the helical layer, the carbon fibers are densely arranged in the region closer to the turn-back position of the carbon fibers, so the strength in that region can be improved in the fiber direction, but not in the direction perpendicular to the fiber direction. Specifically, the high-angle helical layer can mainly improve the strength in the fiber direction in the region relatively close to the boundary between the cylindrical portion and the head portion, i.e., in the circumferential direction where the turn-back position of the fibers exists (Figure 5(A)), while the low-angle helical layer can mainly improve the strength in the fiber direction in the region relatively close to the nozzle part of the head portion, i.e., in the circumferential direction where the turn-back position of the fibers exists (Figure 5(B)).

[0069] Furthermore, in theory, the stress generated in the circumferential direction of the vessel when the vessel is subjected to internal pressure is approximately twice as great as the stress generated in the axial direction of the vessel. Therefore, the placement of the hoop layer is important to increase the burst strength in the burst test and to meet the standard value. On the other hand, as mentioned above, if only the reinforcement of the vessel body is focused, the head part is more likely to be fractured or broken, so the placement of the helical layer is also important to reinforce the head part.

[0070] In the present invention, by arranging helical layers at various angles, it is possible to obtain a pressure vessel with a head portion having stable strength.

[0071] In the present invention, helical layers with different angles are arranged, and the fibers are stacked in the helical layers, and the carbon fiber fold positions are appropriately distributed around the dome-shaped head section. The presence of helical layers with various angles significantly improves the strength of the head section, which is prone to becoming a weak point, and makes it possible to improve the burst strength of the fiber-reinforced pressure vessel.

[0072] In the method for producing a pressure vessel of the present invention, it is preferable to apply pressure to the inside of the vessel in the process of heating the pressure vessel and curing the matrix resin after the FW process, etc. The internal pressure applied to the inside of the liner is preferably in the range of 0.2 MPa or more and 0.6 MPa or less, which makes it possible to cure the matrix resin while maintaining the shape of the pressure vessel.

[0073] During this heating, it is also preferable to rotate the pressure vessel at a constant speed to prevent the reinforcing resin in the reinforced layer from dripping, which makes it easier to prevent the reinforcing resin used in the fiber-reinforced layer from dripping.

[0074] The fiber-reinforced pressure vessel of the present invention can further improve burst pressure, thereby increasing the safety factor and providing a margin for the maximum filling pressure, pressure test pressure, and minimum burst pressure. Here, the maximum filling pressure is the pressure that serves as a guide for the filling volume when using a pressure vessel. The pressure test pressure is the pressure set in a demonstration test conducted at a pressure higher than the design pressure to confirm the safety of the pressure vessel. The minimum burst pressure is "a pressure of 3.33 times or more the maximum filling pressure" or "the pressure at which the stress in the carbon fiber in the liner body, calculated using the design thickness including the glass fiber layer, reaches the stress at which the carbon fiber breaks" (e.g., "Technical Standards for General Composite Vessels Made of Aluminum Alloy Liners and Carbon Fiber KHKS0121(2016)").

[0075] More specifically, the following configurations are conceivable as examples of pressure vessels that have a burst pressure exceeding 180 MPa and exhibit a favorable burst mode with the rupture location at the center of the vessel body. That is, it is a 24-liter pressure vessel having the winding order and configuration of the fiber layers shown in Table 1 below.

[0076] [Table 1]

[0077] Incidentally, if a bursting test is conducted and the bursting pressure exceeds 180 MPa, the container will have a pressure resistance of over 175 MPa, which is the minimum bursting pressure of 157.5 MPa required by the GTR13 standard (Global Technical Regulation No. 13 "Global Standard for Hydrogen and Fuel Cell Vehicles"), with a safety margin of 10% to take into account variations during manufacturing.

[0078] In order to further increase the burst pressure, it is preferable that the pressure vessel be a 24 liter vessel having the winding order and configuration of the fiber layers as shown in Table 2 below.

[0079] [Table 2]

[0080] For the shape of the pressure vessel of the present invention, the dimensions of the liner body 211, such as length, outer diameter, inner diameter, and thickness of the liner body, can be determined according to the purpose, and these dimensions determine the volume of the pressure vessel. For the liner bottom 212 and liner head 213, the mass, thickness of each part, etc. can be determined. For the fiber-reinforced members such as CFRP and GFRP, the thickness, etc. can be determined.

[0081] Furthermore, the volume, mass, diameter, length, pressure setting, etc. of a pressure vessel can be determined depending on the purpose, with the volume corresponding to the capacity and the diameter corresponding to the external dimensions. Important pressure settings include the nominal operating pressure, maximum filling pressure, pressure test pressure, minimum burst pressure, and design burst pressure. It is preferable to determine these physical properties by taking into consideration the balance between the consumption rate and consumption amount over time of the gas used, the dimensions of the container relative to the installation location, and the pressure of the gas used.

[0082] The fiber-reinforced pressure vessel of the present invention is not limited in capacity and can be applied in a wide range, generally from 0.8 liters to 800 liters.

[0083] When the pressure container of the present invention is used as an air cylinder for firefighting, for example, it can be used for typical volumes of 4 liters (4 to 5 liters), 6 liters (6 to 7 liters), and 8 liters (8 to 9 liters). The filling pressure of the pressure container of the present invention is preferably set in the range of 29 to 30 MPa for 4 liter and 6 liter sizes, and in the range of 14 to 15 MPa or 29 to 30 MPa for 8 liter sizes. With these volumes, for example, if a firefighter uses an air cylinder during a disaster and consumes 40 liters of air per minute, the estimated working time at the disaster site can be approximately 30 minutes, 45 minutes, or 60 minutes or more. Example: 29 MPa (approximately 300 atmospheres) x volume 4 liters = approximately 1200 liters Approximately 1200 liters / (approximately 40 liters / minute) = approximately 30 minutes

[0084] Similarly, when used as an FRP pressure vessel for hydrogen gas in an automobile-related fuel cell (FC), assuming an expected driving distance of 500 to 1,000 km and a required volume of 7 to 9 kg of hydrogen gas (80,000 to 100,000 liters), a volume of 100 to 150 liters is preferred for the FRP pressure vessel to be mounted on the automobile body when filled with a container at a filling pressure of 70 MPa. Furthermore, assuming that the vessels are mounted in separate compartments, a volume of 20 to 100 liters per container is also preferred. Of course, it is preferable to appropriately adjust the size and shape of the FRP pressure vessel to accommodate the various interior components mounted on the automobile body so as not to interfere with these components. Furthermore, by mounting the vessels in separate compartments, the main FRP pressure vessel can be used during normal driving, and when fuel runs low or minor trouble occurs, the sub-FRP pressure vessel can be used for driving. Furthermore, from the perspective of fuel economy, a lightweight pressure vessel is preferred.

[0085] Naturally, a pressure vessel with a large volume has a large mass, and a pressure vessel with a high maximum filling pressure and a large thickness also has a large mass. Also, a pressure vessel with a large volume, i.e., a large mass, can supply gas for a long period of time, but because of its large mass, it tends to lose gas quickly when used, which can make it inefficient.

[0086] To increase the gas capacity of a pressure vessel, you can either increase the filling pressure or increase the vessel's volume. There are two ways to increase a pressure vessel's volume: "increasing its length" or "increasing its external dimensions." Generally, the burst pressure of a pressure vessel is correlated with the vessel's thickness relative to its external dimensions. Therefore, "increasing its length" allows for smaller external dimensions and a smaller thickness, while "increasing its external dimensions" requires a larger thickness, but allows for a smaller length. Therefore, depending on where the pressure vessel is installed, it is necessary to maintain the vessel's volume while considering the balance between its length, external dimensions, thickness, and mass. Additionally, the pressure vessel must be designed to meet the standard burst pressure for burst tests and ensure that the rupture location is not in the head section.

[0087] The pressure vessel of the present invention has optimally arranged reinforcing fibers, making it lightweight, easy to work with, and able to withstand high pressures, making it a highly practical pressure vessel. Furthermore, the pressure vessel of the present invention has a strong head, little variation in burst pressure, and is stable to a high standard.

[0088] The fiber-reinforced pressure vessel of the present invention is ideally suited for use as a container for storing air used by divers, firefighters, etc., oxygen used by patients infected with COVID-19, and hydrogen used by mobile vehicles such as automobiles and drones. [Example]

[0089] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited thereto. The values in the examples were determined by the following methods.

[0090] (1) Destructive test (burst test) The test was conducted in accordance with paragraphs 6.2.2.1 and 5.1.1.1 of International Technical Regulation No. 13. Specifically, the test was conducted using the following method: the interior of the fiber-reinforced pressure vessel specimen was filled with water, and the pressure was gradually increased using water pressure. The pressure was maintained at the specified pressure (10 MPa) to confirm airtightness. The pressure was then increased further, and the pressure at the time of failure and the location of failure were recorded. Test specimen pressurizing medium: Water Pressure medium temperature: 15~25℃ Testing room temperature and humidity: 20-25°C, 50-75% Pressure increase pattern: Apply pressure at 5 MPa / min, hold at 10 MPa for 1 minute, then increase pressure again until failure occurs.

[0091] (2) Fatigue cycle test The test was carried out in accordance with paragraphs 6.2.2.2 and 5.1.1.2 of International Technical Regulation No. 13. That is, the test was carried out according to the following method. Three containers randomly selected from the ten will be subjected to a room temperature pressure cycle test. Fill the container with non-corrosive water, and then stabilize the container and liquid at 20±5°C. -2±1MPa and 87.5MPa or more, which is 125% of the NWP (nominal working pressure: 70MPa), are applied alternately at a rate of 10 times or less per minute until a leak occurs or up to 45,000 times. Test specimen pressurizing medium: Water Pressure medium temperature: 15~25℃ Testing room temperature and humidity: 20-25°C, 50-75%

[0092] [Example 1] The liner was made of nylon resin. The ends of two bowl-shaped resin molded articles obtained by injection molding nylon resin were hot-plate welded together to produce a 24-liter liner with a body length of 292 mm, an outer diameter of 300 mm, a thickness of 5 mm, and a weight of 2.4 kg. The hot-plate welding conditions were a hot-plate temperature of 240°C and a welding time of 60 seconds.

[0093] The liner nozzle was made of aluminum alloy A6061-T6, and a sealant was used to bond the nozzle and liner.

[0094] The reinforcing fiber bundles used to reinforce the liner were Tenax-E UTS50 24K (Tex 1600g / km, tensile strength 5100MPa, tensile modulus 245GPa) manufactured by Teijin Limited. The fiber bundle tow width was 8-9mm. The matrix resin that forms the reinforcing layer together with the carbon fiber was a base epoxy resin mixed with a curing acid, curing accelerator, and antifoaming agent. The weight ratio of base resin:curing agent:curing accelerator:antifoaming agent was 100:120:1:1.

[0095] First, four reinforcing fiber bundles were aligned and immersed in a resin tank containing an epoxy resin composition to form a fiber-reinforced resin material. Then, hoop winding and helical winding were performed in the order shown in Table 3 so that the band width of the fiber-reinforced resin material on the liner was 15 mm, and the material was wound around the liner at the winding angle and thickness shown in Table 3. The tension applied to the fiber bundle during winding was 5 N per fiber bundle. The pressure inside the liner was 0.1 MPa at the start of winding and 0.2 MPa after the hoop winding and high-angle helical winding layers were completed.

[0096] After wrapping the fiber-reinforced resin material in this way, the matrix resin was hardened by heating at the temperature and time shown in Figure 6 while maintaining the pressure inside the liner at 0.2 MPa, resulting in a fiber-reinforced pressure vessel with a reinforcing layer formed on the liner. The Vf (volume fiber content) of the reinforcing layer, calculated from the amount of carbon fiber used and the weight of the reinforcing layer, was 70%.

[0097] The resulting fiber-reinforced pressure vessel was subjected to a burst test, and the vessel burst at 160.3 MPa, demonstrating a relatively good burst pressure and fracture morphology. Furthermore, a fatigue cycle test was conducted, and no burst or leakage occurred even after over 45,000 cycles. The measurement results are shown in Table 8.

[0098] [Table 3]

[0099] [Example 2] High-density polyethylene resin was used as the liner material instead of the nylon resin used in Example 1. The resin used for the liner was rotationally molded to obtain a liner with a body length of 378 mm, an outer diameter of 224 mm, a thickness of 5 mm, and a volume of 17 liters. The material composition and curing temperature other than the raw resin of the liner were the same as in Example 1, except that the winding order of the fiber bundle was changed as shown in Table 4. When a burst test was conducted on the fiber-reinforced pressure vessel, it burst from the barrel at 170.5 MPa, showing a relatively good burst pressure and fracture mode. The measurement results are also shown in Table 8.

[0100] [Table 4]

[0101] [Example 3] A fiber-reinforced pressure vessel having a volume of 24 liters was obtained under the same conditions as in Example 1, except that the winding order of the fiber bundle was changed as shown in Table 5. When a burst test was conducted on a fiber-reinforced pressure vessel, it burst from the barrel at 126.4 MPa. Although the burst pressure was not large, the expected location of the rupture and a good rupture pattern were observed. The measurement results are also shown in Table 8.

[0102] [Table 5]

[0103] [Comparative Example 1] A fiber-reinforced pressure vessel having a volume of 17 liters was obtained under the same conditions as in Example 2, except that the winding order of the fiber bundle was changed as shown in Table 6. When a burst test was conducted on a fiber-reinforced pressure vessel, it burst at the head section at 129.4 MPa. However, the burst pressure was not large, and the expected location of the failure was at a different head section, resulting in an unintended failure pattern. The measurement results are also shown in Table 8.

[0104] [Table 6]

[0105] Comparative Example 2 A fiber-reinforced pressure vessel having a volume of 17 liters was obtained under the same conditions as in Example 2, except that the winding order of the fiber bundle was changed as shown in Table 7. A fiber-reinforced pressure vessel was subjected to a burst test, and the vessel burst at 141.4 MPa from the head section. The burst pressure was higher than that of Comparative Example 1, but not as high as expected. Furthermore, the vessel failed at a different location than expected, resulting in an unintended failure mode. The measurement results are also shown in Table 8.

[0106] [Table 7]

[0107] Table 8 shows a summary of the measurement results for Examples 1, 2, and 3 and Comparative Examples 1 and 2.

[0108] [Table 8] [Explanation of symbols]

[0109] R0: Radius of the cylinder R1: Distance from the center of the mirror (dome) (central axis AX) to the folding position of the reinforcing fiber α0: Winding angle of reinforcing fiber in the cylinder part AX: Central axis 200: Pressure vessel 201: Torso 202: Bottom 203: Head 204: Storage space 205: Plug member 206: nozzle 207:Aperture 210: Rina 211: Liner body 212: Bottom of liner 213: Liner head 220: Fiber reinforced resin layer (reinforcement layer) 221: Reinforcement fiber 250: Valve assembly

Claims

1. A fiber-reinforced pressure vessel comprising an airtight liner and a fiber-reinforced resin layer, wherein the reinforcing fibers are carbon fibers, and the winding angle of the fibers in the fiber-reinforced resin layer relative to the axis of the liner is: Hoop layer of 85 degrees or more, A high-angle helical layer having an angle of 75 degrees or more and less than 85 degrees; a low-angle helical layer of less than 30 degrees; and A fiber-reinforced pressure vessel characterized in that the thickness ratio of the hoop layer in the fiber-reinforced resin layer is 15 to 70%, the thickness ratio of the low-angle helical layer is 20 to 70%, and the thickness ratio of the high-angle helical layer is in the range of 0.5 to 10%.

2. In the fiber reinforced resin layer, the winding angle of the fiber relative to the axis of the liner is: A high-angle helical layer of 60 degrees or more and less than 75 degrees; Or a medium-angle helical layer of 30 degrees or more and less than 60 degrees, 2. The fiber-reinforced pressure vessel of claim 1, further comprising layers of:

3. 2. The fiber-reinforced pressure vessel according to claim 1, wherein the ratio of the total thickness of the hoop layer and the high-angle helical layer in the fiber-reinforced resin layer is in the range of 16 to 48%.

4. 2. The fiber-reinforced pressure vessel according to claim 1, further comprising a high-angle helical layer of 60 degrees or more but less than 75 degrees, the high-angle helical layer occupying 1 to 20% of the thickness of the vessel.

5. 2. The fiber-reinforced pressure vessel according to claim 1, further comprising a medium-angle helical layer of 30 degrees or more but less than 60 degrees, the thickness ratio of the medium-angle helical layer being in the range of 1 to 20%.

6. 2. The fiber-reinforced pressure vessel of claim 1, wherein the hoop layers are disposed on either side of the helical layers.

7. 2. The fiber-reinforced pressure vessel according to claim 1, wherein the hoop layers are arranged in the innermost and outermost layers.

8. 2. The fiber-reinforced pressure vessel according to claim 1, wherein the liner is made of a synthetic resin or an aluminum alloy.

9. 2. The fiber-reinforced pressure vessel according to claim 1, wherein the resin used in the fiber-reinforced resin layer is a thermosetting resin.

10. A method for manufacturing a fiber-reinforced pressure vessel, characterized in that when winding a resin-impregnated carbon fiber bundle around the surface of an airtight liner, at least the following layers are formed: a hoop layer with a fiber winding angle of 85 degrees or more, a high-angle helical layer with a winding angle of 75 degrees or more but less than 85 degrees, and a low-angle helical layer with a winding angle of less than 30 degrees relative to the axis of the liner, with the hoop layer thickness ratio being 15 to 70%, the low-angle helical layer thickness ratio being 20 to 70%, and the high-angle helical layer thickness ratio being 0.5 to 10%.

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