JP2025116307A - Fiber-reinforced pressure vessel and its manufacturing method - Google Patents

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

The present invention relates to a fiber-reinforced pressure vessel for storing high-pressure gases, etc., and more specifically to a fiber-reinforced pressure vessel in which an airtight liner is reinforced with a fiber-reinforced resin layer.

Fiber-reinforced pressure vessels, which have a metal or resin liner wrapped in resin-impregnated fibers, are widely used as containers for filling high-pressure gases, liquefied gases, etc. They are extremely lightweight and easy to handle compared to steel containers of the same size, and are therefore widely used.

In such fiber-reinforced pressure vessels, the liner primarily functions as a component that prevents the permeation of gases and other substances, providing airtightness, while the resin-impregnated fiber layer primarily functions as a component that provides the strength to withstand high internal pressure. Therefore, when designing a fiber-reinforced pressure vessel to withstand high internal pressure, the configuration of the resin-impregnated fiber layer is extremely important.

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

However, these configurations still had the problem of not being able to achieve stable, high burst strength in burst tests.

JP 2008-32088 A Japanese Patent Application Laid-Open No. 2004-176898

The present invention was developed in light of the above background, and its purpose is to provide a fiber-reinforced pressure vessel that is lightweight yet has excellent burst strength during a burst test.

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 three layers: a hoop layer with a fiber winding angle of 85 degrees or more relative to the liner axis, a high-angle helical layer with a fiber winding angle of 75 degrees or more but less than 85 degrees, and a low-angle helical layer with a fiber winding angle of less than 30 degrees; the thickness of the hoop layer in the fiber-reinforced resin layer is 15 to 70%, the thickness of the low-angle helical layer is 20 to 70%, and the thickness of the high-angle helical layer is 0.5 to 10%.

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 is 30 degrees or more but less than 60 degrees.

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 be in the range of 16 to 48%, that the high-angle helical layer is between 60 degrees and less than 75 degrees, and that its thickness ratio be in the range of 1 to 20%, and that the medium-angle helical layer is between 30 degrees and less than 60 degrees, and that its thickness ratio be in the range of 1 to 20%.

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.

Another method of manufacturing a fiber-reinforced pressure vessel of the present invention involves winding resin-impregnated carbon fiber bundles around the surface of an airtight liner, forming at least a hoop layer with a fiber winding angle of 85 degrees or more relative to the liner axis, 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, with the hoop layer thickness ratio being 15-70%, the low-angle helical layer thickness ratio being 20-70%, and the high-angle helical layer thickness ratio being 0.5-10%.

The present invention provides a fiber-reinforced pressure vessel that is lightweight yet has excellent burst strength during burst tests.

1 is a cross-sectional view showing a schematic structure of a fiber-reinforced pressure vessel of the present invention. FIG. 1 is a conceptual diagram of hoop winding in a fiber-reinforced pressure vessel. 1 is a conceptual diagram of high-angle helical winding in a fiber-reinforced pressure vessel. 1 is a conceptual diagram of low-angle helical winding in a fiber-reinforced pressure vessel. 1 is a conceptual diagram showing the difference in the reinforcing effect on the mirror portion (dome portion) depending on the angle of the helical winding. 10 is a graph showing heat treatment conditions after a fiber reinforced resin material is wound around a liner.

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. The fiber-reinforced resin layer is characterized by having at least three layers, each with a fiber winding angle relative to the liner axis: 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 be 15 to 70%, the low-angle helical layer be 20 to 70%, and the high-angle helical layer be 0.5 to 10%.

The winding angle of the fibers in each layer is determined by taking the hoop winding, which is wound approximately perpendicular to the tank axis of the container in the body of the container, as "85 degrees or more" (winding perpendicular to the tank axis is "90 degrees"; "α1" in Figure 2), and winding parallel to the tank axis as "0 degrees." For example, the angle of various helical windings corresponds to the angle "α2" in Figure 3. In addition, to level out the fiber reinforcement, each angle is usually used as a pair of two directions, "+" (plus) and "-" (minus), and the thickness ratios shown above are the total amount of layers with the corresponding angle in the fiber-reinforced resin layer.

As long as the thickness ratios of each layer are met, it is also preferable to have a "high-angle helical layer of 60 degrees or more but less than 75 degrees" and/or a "medium-angle helical layer of 30 degrees or more but 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. This allows the glass-fiber-reinforced resin layer to prevent surface damage, which is likely to occur when the container is used, and protects the carbon-fiber-reinforced resin layer.

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

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%, but it is more preferable that it be in the range of 40 to 60%, and especially 45 to 55%.

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

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.

It is also preferable that the innermost layer, including the first layer that contacts the liner, be a hoop layer. It is also preferable to place a hoop layer on the outermost layer, as this makes it easier to suppress the occurrence of voids and sagging of the fiber bundles in the helical layer. In the barrel 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. However, as mentioned above, focusing only on reinforcing the barrel makes the head portion (dome portion) more susceptible to fracture and damage, so the placement of a helical layer is also important for reinforcing the head portion.

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 bending of the helically wound fiber bundle that is wound over the hoop winding.

Regarding the "helical layer," it is preferable that the folding positions in the overlapping head section are not consecutively folded with the same folding diameter, but that each layer is offset by at least half the fiber bundle width. This prevents distortion of the carbon fiber reinforced resin lamination in the head section and reduces areas where undue stress is concentrated.

In the fiber-reinforced pressure vessel of the present invention, by limiting the maximum angle helical layer and other layer configurations to the above ranges, the rupture strength of the fiber-reinforced pressure vessel during a burst test can be increased, and the primary rupture site can be located in the barrel rather than the head (dome) section. Generally, pressure vessels with this type of structure have greater strength variation in the head section than in the barrel, and a pressure vessel that consistently ruptures in the barrel section 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 rather than the head section.

The carbon fibers used in the fiber-reinforced resin layer preferably have a tensile modulus of 200 GPa or more, and 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.

The carbon fiber used as such reinforcing fiber is preferably a fiber bundle composed of a large number of filaments, preferably 2,000 (2K) or more, more preferably 4,000 (4K) to 40,000 (40K), and especially preferably in the range of 8,000 (8K) to 32,000 (32K). Using such fiber bundle-shaped reinforcing fiber makes it possible to efficiently wind a large number of reinforcing fibers onto the liner.

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

Furthermore, with reference to the drawings, a preferred embodiment of the fiber-reinforced pressure vessel of the present invention will be described. Note that in the drawings, the same or corresponding parts are designated by the same reference numerals. Note that the present invention is not specifically limited to the following drawings, etc.

First, referring to Figure 1, the structure of the fiber-reinforced pressure vessel (hereinafter sometimes referred to as "FRP pressure vessel" or "pressure vessel") of the present invention will be described.

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

The body 201 is a cylindrical portion of the pressure vessel 200 with approximately uniform outer dimensions. The bottom 202 is located at the bottom of the pressure vessel 200 and is located 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 located at the top of the pressure vessel 200 and is located at the other end of the body 201 opposite the bottom. The head 203 is provided with a nozzle 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 the two ends of the liner. The top of the liner is fixed by the nozzle 206, and the bottom of the liner is fixed by a jig. The plug member 205 is the remaining part after the jig is cut.

The pressure vessel 200 also has a storage space 204 inside that stores 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, the storage space 204 is filled with a fuel gas, typically hydrogen, at high pressure, and this fuel gas is then decompressed and used to generate electricity in the fuel cell.

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 aluminum alloy or stainless steel. A female thread (not shown) is formed on the inner circumferential surface of the opening 207 provided in the nozzle 206. The valve assembly 250 or piping can be screwed into the nozzle 206 via the female thread.

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, which integrates piping elements such as valves and fittings. 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.

The pressure vessel 200 also has a fiber-reinforced resin layer 220 (hereinafter sometimes referred to as the "reinforcement layer") on the surface of the liner 210. The liner 210 is disposed inside the pressure vessel 200 and is a component that hermetically contains gas or liquid. The liner 210 has 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.

The liner 210 has the function of suppressing the permeation of gas or liquid stored in the storage space 204 and preventing the gas or liquid from coming into contact 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 barrier properties against gas or liquid. The liner 210 can be made of aluminum alloy, resin material, non-metallic elastic material, etc.

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.

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.

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.

First, in step 1, an aluminum alloy plate is prepared and placed in a machine tool. The aluminum alloy plate is preferably a disk-shaped plate made of aluminum alloy. Then, in step 2, the aluminum alloy plate is subjected to press cupping. In step 2, the bottom 202, which is the dome-shaped portion at the bottom of the pressure vessel 200, is formed. Next, in step 3, the press-cupped cup-shaped aluminum alloy is subjected to forming, also known as stretching. In step 3, the body 201, which is the 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, with one end open.

In step 4, the roughly test-tube-shaped aluminum alloy opening machined in steps 1 to 3 is subjected to a spinning process. In step 4, the head 203, which is the dome-shaped portion at the top of the pressure vessel 200, is formed. Through steps 2 to 4, the pressure vessel 200 is roughly finished into the vessel shape. In step 5, heat treatment is performed. In step 6, thread cutting 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.

The fiber-reinforced pressure vessel of the present invention has a structure in which a fiber-reinforced resin layer is wrapped around a resin or aluminum alloy liner as described above. The fibers in the fiber-reinforced resin layer used in the present invention contain carbon fibers, constituting a so-called CFRP (carbon fiber reinforced plastic) reinforcing layer.

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

Furthermore, to prevent a decrease in strength, the volume content of the matrix resin in the carbon fiber reinforced resin is preferably 25% or more and 45% or less. (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 occurrence of fiber fuzz 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.

In other words, the reinforcing layer 220, which is a fiber-reinforced resin layer, primarily compensates for the strength deficiencies of the liner 210 alone, thereby increasing the strength of the pressure vessel 200. The reinforcing layer 220 of the present invention is composed of FRP (Fiber Reinforced Plastics), 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, a particularly preferred embodiment of the present invention is a pressure vessel in which a CFRP layer and a GFRP layer are laminated in order around the outer periphery of the liner 210, forming a reinforcing layer 220 in which the outermost layer is a GFRP layer.

Furthermore, 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.

In other words, this manufacturing method involves winding a resin-impregnated carbon fiber bundle around the surface of an airtight liner, forming at least a hoop layer with a fiber winding angle of 85 degrees or more relative to the liner axis, 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, with the hoop layer thickness ratio being 15-70%, the low-angle helical layer thickness ratio being 20-70%, and the high-angle helical layer thickness ratio being 0.5-10%.

Here, it is preferable to move the end position of the hoop winding closer to the center of the cylindrical body for each layer. This reduces the height difference at both ends of the hoop winding, reducing the bending of the helically wound fiber bundle wound over the hoop winding.

When overlapping helical windings, it is preferable not to continuously overlap the helical windings with the same fold diameter at the fold position in the head section, and it is even more preferable to offset the folds by more than half the fiber bundle width. This prevents distortion of the laminated shape of the carbon fiber reinforced resin in the head section and reduces the number of areas where stress is concentrated.

It is also preferable to wind a hoop layer as the first layer, which will enable more stable, less variable, high burst strength and burst behavior at the center of the cylindrical body in burst tests. It is also preferable to place a hoop layer as the outermost layer, which will better suppress the occurrence of voids in the helical layer and sagging of the fiber bundles.

An example of the process for forming the reinforcing layer 220 is 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, reinforcing fibers such as carbon fiber pre-impregnated with a thermosetting resin, typically epoxy resin, or in some cases other glass fiber, are wound around the outer periphery of the liner 210, and the thermosetting resin is thermally cured to form the reinforcing layer 220.

In addition, when winding 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. By applying an appropriate amount of internal pressure, it is possible to suppress dents and deformation of the liner during the FW process.

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 helps prevent the fiber bundle from sagging. However, applying too much tension tends to increase the likelihood of problems such as fuzzing and thread breakage.

The winding speed of carbon fiber reinforced resin onto 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. A winding speed above the lower limit is preferable to improve productivity, but winding at a speed above the upper limit tends to cause fiber bundle slippage and resin scattering, particularly when the helical winding angle is low. However, if ingenuity and improvements can be made to solve the issues of preventing fiber bundle slippage and resin scattering, winding at speeds above the upper limit is possible, leading to further improvements in productivity and therefore acceptable.

The matrix resin used in carbon fiber reinforced resin is preferably a thermosetting resin, with epoxy resin being more preferred. Other possible matrix resins include phenolic resin, vinyl ester resin, and unsaturated polyester resin. One type of matrix resin may be used alone, or two or more types may be used in combination.

To prevent a decrease in strength, the volume content of the matrix resin in carbon fiber reinforced resin is preferably 25% or more and 45% or less. (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 prevent fiber fuzz and voids between fiber bundles during processing. Impregnating the resin at a volume content below the upper limit helps to prevent fiber bundle slippage and resin sagging during winding.

Methods for winding reinforcing fibers such as carbon fiber and glass fiber include hoop winding and various helical windings, as mentioned above. In one example of the most preferred embodiment, a fiber wound layer of carbon fiber reinforced resin is laminated around 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 this embodiment of the present invention, it is essential to first laminate multiple fiber wound layers with different carbon fiber winding methods around 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 onto the fiber wound layer of carbon fiber reinforced resin formed around the outer periphery of the liner 210, as needed.

As shown in Figure 2, hoop winding is a method of winding reinforcing fibers 221, such as carbon fibers or glass fibers, around the cylindrical liner 210 at a winding angle approximately 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 direction of movement of the 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 hoop winding is 85 to 90 degrees, and the fiber winding layer formed by hoop winding is the hoop layer. Because it is difficult to wind the reinforcing fibers 221 around the liner bottom 212 and liner head 213 using hoop winding, the hoop layer is generally formed over the entire liner body 211. In other words, the hoop layer is important for improving the circumferential strength of the body of the pressure vessel 200.

As shown in Figure 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 this 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 this invention, it is particularly important to have a "high-angle helical layer (75 degrees to less than 85 degrees)."

Figure 3 shows the reinforcing fiber 221 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 in the liner body 211. Note that 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, but in the present invention, the presence of a "low-angle helical layer of less than 30 degrees" and a "high-angle helical layer of 75 degrees or more and less than 85 degrees" is particularly important.

Note that "high-angle helical layers," "high-angle helical layers," and "hoop layers" with a winding angle of 60 degrees or more have a relatively large winding angle that allows the reinforcing fiber 221 to make at least one full turn in the liner barrel 211. Conversely, "low-angle helical layers of less than 30 degrees" such as those in Figure 4 have a relatively small winding angle (angle α3 in Figure 4) that allows the winding direction to be changed before the reinforcing fiber 221 makes one full turn in the liner barrel 211. Note that the winding angle is sometimes referred to as the orientation angle.

Incidentally, the effect of improving the strength of the mirror portion varies depending on the angle of the helical winding.
5A and 5B are schematic diagrams illustrating the improvement in the strength of the mirror portion due to helical winding. Each of the diagrams shows the mirror portion as viewed along the central axis AX. The mirror portion in Fig. 5A has a high-angle helical winding, while the mirror portion in Fig. 5B has a low-angle helical winding.

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.
R ₁ =R ₀・sin α ₀ ...(1)

Here, _R0 is the radius of the cylinder portion, and _α0 is the winding angle of the carbon fiber around the cylinder portion. _R1 is the distance from the center of the head portion (central axis AX) to the folding position of the carbon fiber. Specifically, the "folding position of the carbon fiber" means the position of the apex of the curve drawn by the carbon fiber on the head portion. When the carbon fiber is repeatedly folded in the winding direction around the head portion so that the above formula (1) holds, the folding position of the carbon fiber will be located on the circumference of a circle with a radius of _R1 on the head portion.

If the folding position of the carbon fiber is set at a position that is deviated from the position calculated by equation (1) above, 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.If the position is shifted toward the die, the tension of the carbon fiber at the folding position will cause it to shift toward the die during FW molding.This could result in molding defects and potential failure points.For this reason, this "folding position of the carbon fiber" is extremely important in improving and stabilizing the strength of the molding surface of the head portion.

In general, 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.

In the helical layer, the carbon fibers are densely arranged in the region closer to the folding position of the carbon fibers, which improves the strength in the fiber direction in that region, but does not improve the strength in the direction perpendicular to the fiber direction. Specifically, the high-angle helical layer mainly improves the strength in the fiber direction in the region relatively close to the boundary between the cylindrical portion and the mirror portion, i.e., the circumferential direction where the folding position of the fibers exists (Figure 5(A)). In the low-angle helical layer, the strength in the fiber direction in the region relatively close to the nozzle portion of the mirror portion, i.e., the circumferential direction where the folding position of the fibers exists (Figure 5(B)).

Furthermore, in theory, the stress generated in the circumferential direction of a pressure vessel when subjected to internal pressure is roughly twice as great as the stress generated in the axial direction of the vessel. Therefore, the placement of hoop layers 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 vessel's body makes it more likely that fractures or damage will occur in the head section, so the placement of helical layers is also important for reinforcing the head section.

In this invention, by arranging helical layers at various angles, it is possible to obtain a pressure vessel with stable head strength.

In this invention, helical layers with different angles are arranged, fibers are stacked within the helical layers, and the carbon fiber fold positions are appropriately distributed around the dome-shaped head section. The presence of helical layers with such 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.

In addition, in the manufacturing method of the pressure vessel of the present invention, after the above-mentioned FW process, etc., it is preferable to pressurize the inside of the vessel in the process of heating the pressure vessel and curing the matrix resin. 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.

In addition, during this heating process, it is 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.

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 amount when using a pressure vessel. The pressure test pressure is the pressure set in a demonstration test conducted at a pressure above 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, becomes the stress that breaks the carbon fiber" (e.g., "Technical Standards for General Composite Vessels Made of Aluminum Alloy Liners and Carbon Fiber, KHKS0121 (2016)").

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

By the way, if a bursting test is conducted and the bursting pressure exceeds 180 MPa, the container will have a pressure-resistant bursting pressure of over 175 MPa, calculated by adding a 10% safety margin to 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") to take into account manufacturing variations.

To further increase the burst pressure, it is preferable to use a pressure vessel with the winding order and configuration of the fiber layers as shown in Table 2 below for a 24-liter container.

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 the volume of the pressure vessel is determined by these dimensions. For the liner bottom 212 and liner head 213, the mass, thickness of each part, etc. can be determined. For the fiber-reinforced members CFRP and GFRP, the thickness, etc. can be determined.

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 various specifications by taking into account 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.

The fiber-reinforced pressure vessel of the present invention can be applied to a wide range of volumes without any limitations. Typical volumes are 0.8 liters to 800 liters.

When the pressure vessel 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 vessel of the present invention is preferably set in the range of 29 to 30 MPa for 4 liter and 6 liter volumes, and in the range of 14 to 15 MPa or 29 to 30 MPa for 8 liter volumes. With such 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, approximately 45 minutes, or approximately 60 minutes or more.
Example: 29 MPa (approximately 300 atmospheres) x 4 liters of volume = approximately 1,200 liters. Approximately 1,200 liters / (approximately 40 liters/minute) = approximately 30 minutes

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), and a filling pressure of 70 MPa, the FRP pressure vessel mounted on the automobile body preferably has a volume of 100 to 150 liters. Furthermore, assuming separate mounting, a volume of 20 to 100 liters per vessel is also preferable. Of course, it is preferable to appropriately change 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 separately, 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 automobile fuel economy, a lightweight pressure vessel is preferable.

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. Furthermore, while a pressure vessel with a large volume, i.e. a large mass, can supply gas for a long period of time, it can also be inefficient because the gas used decreases quickly due to its large mass.

Increasing the gas capacity of a pressure vessel can be achieved by either increasing the filling pressure or by increasing the vessel's volume. There are two ways to increase the volume of a pressure vessel: by increasing its length or by 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, in the former case, increasing the length allows for smaller external dimensions and a smaller thickness, while in the latter case, increasing the external dimensions requires an increase in thickness, but the length can be reduced. 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 clear the standard burst pressure in burst tests and ensure that the rupture location is not in the head section.

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.

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.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. The values in the examples were determined using the following methods.

(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 as follows: The interior of a 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 further increased, and the pressure at which the vessel broke and the location of the break were recorded.
・Test specimen pressure medium: Water ・Pressure medium temperature: 15 to 25°C
・Test room temperature and humidity: 20-25℃, 50-75%
Pressure increase pattern: Apply pressure at 5 MPa/min, hold at 10 MPa for 1 minute, then increase pressure again until fracture occurs.

(2) Fatigue cycle test: This test was carried out in accordance with Sections 6.2.2.2 and 5.1.1.2 of the 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.
- After filling the container with water, a non-corrosive liquid, the container and liquid are stabilized at 20±5°C.
- Pressurize the valve between 2±1 MPa and 87.5 MPa or more, which is 125% of the NWP (nominal working pressure: 70 MPa), at a rate of 10 times or less per minute until leakage occurs or up to 45,000 times.
・Test specimen pressure medium: Water ・Pressure medium temperature: 15 to 25°C
・Test room temperature and humidity: 20-25℃, 50-75%

[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 liner with a body length of 292 mm, an outer diameter of 300 mm, a thickness of 5 mm, a weight of 2.4 kg, and a volume of 24 liters. The hot-plate welding conditions were a hot-plate temperature of 240°C and a welding time of 60 seconds.

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

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

First, four reinforcing fiber bundles were aligned and immersed in a resin tank containing an epoxy resin composition to create 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 wrapped around the liner at the winding angle and thickness shown in Table 3. The tension applied to the fiber bundles 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.

After wrapping the fiber-reinforced resin material in this manner, 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%.

A burst test was conducted on the resulting fiber-reinforced pressure vessel, which burst from the barrel at 160.3 MPa, demonstrating relatively good burst pressure and fracture morphology. Furthermore, a fatigue cycle test was conducted, and no burst or leakage occurred, even after more than 45,000 cycles. The measurement results are shown in Table 8.

[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 carried out 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.

[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 fiber-reinforced pressure vessel was subjected to a burst test, it burst from the barrel at 126.4 MPa. Although the burst pressure was not large, the expected location of the failure and a favorable failure pattern were observed. The measurement results are also shown in Table 8.

[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 129.4 MPa from the head section. However, the burst pressure was not large, and the location of the failure was different from the expected location, the head section, resulting in an unintended failure mode. The measurement results are also shown in Table 8.

[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.

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

R ₀ : Radius of the cylinder portion R ₁ : Distance from the center (central axis AX) of the head portion (dome portion) to the folding back position of the reinforcing fiber α ₀ : Winding angle of the reinforcing fiber in the cylinder portion AX: Central axis 200: Pressure vessel 201: Body portion 202: Bottom portion 203: Head portion 204: Storage space 205: Plug member 206: Mouthpiece 207: Opening 210: Liner 211: Liner body portion 212: Liner bottom portion 213: Liner head portion 220: Fiber reinforced resin layer (reinforcing layer)
221: Reinforcement fiber 250: Valve assembly

Claims (10)

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%. 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: A 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%. The fiber-reinforced pressure vessel of claim 1 further comprises a high-angle helical layer of 60 degrees or more but less than 75 degrees, the thickness ratio of which is in the range of 1 to 20%. The fiber-reinforced pressure vessel of claim 1 further comprises a medium-angle helical layer of 30 degrees or more but less than 60 degrees, the thickness ratio of which is in the range of 1 to 20%. A fiber-reinforced pressure vessel according to claim 1, in which the hoop layers are arranged with the helical layers sandwiched between them. A fiber-reinforced pressure vessel according to claim 1, in which hoop layers are arranged in the innermost and outermost layers. The fiber-reinforced pressure vessel of claim 1, wherein the liner is made of synthetic resin or aluminum alloy. The fiber-reinforced pressure vessel according to claim 1, wherein the resin used in the fiber-reinforced resin layer is a thermosetting resin. A method for manufacturing a fiber-reinforced pressure vessel, characterized in that when winding resin-impregnated carbon fiber bundles around the surface of an airtight liner, at least three layers are formed: a hoop layer with a fiber winding angle of 85 degrees or more relative to the liner axis, 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; the thickness of the hoop layer is 15-70%, the thickness of the low-angle helical layer is 20-70%, and the thickness of the high-angle helical layer is 0.5-10%.