Gas cylinder for filling high-pressure oxygen and manufacturing method thereof

Abstract

The invention belongs to the technical field of diffusion welding and thin-wall seamless steel pipe bulging, and relates to a gas cylinder for filling high-pressure oxygen and a manufacturing method thereof, the gas cylinder comprises a thin-wall seamless steel pipe liner, a gas cylinder joint, a Teflon lining coating, a high-molecular polymer layer, a carbon fiber reinforced winding layer and an external protection layer, the bottle body is formed through multiple times of water pressure bulging, and cracks and wrinkles caused by spinning are avoided; electroplating a nickel-iron-PTFE composite layer on the inner surface, and spraying and sintering PTFE to form an antioxidant lining; the outer surface is fully wound with a carbon fiber main bearing structure after being subjected to injection molding of a polyethylene layer, and then is coated with a glass fiber and epoxy resin protective layer. A traditional spinning process is abandoned, forming is uniform, defects are avoided, the connector strength is high, the sealing performance is good, the light weight level, the fatigue life and the use safety of the gas cylinder are remarkably improved, and the gas cylinder is suitable for medical, aviation and other high-purity high-pressure oxygen storage scenes.

Description

Technical Field

[0001] This invention relates to the fields of diffusion welding and thin-walled seamless steel pipe bulging technology, and particularly to a gas cylinder for filling high-pressure oxygen and its manufacturing method. Background Technology

[0002] High-pressure oxygen cylinders are high-pressure containers used for storing and transporting oxygen. They are typically made of alloy structural steel or aluminum alloy and undergo special internal treatment to ensure oxygen purity and safety. Their design and manufacture adhere to stringent standards, allowing them to withstand high pressure and preventing oxygen leakage. The standard filling pressure is 15 MPa (approximately 14.7 atmospheres), with a residual pressure of 0.1–0.2 MPa required. The "Gas Cylinder Safety Supervision Regulations" require a nominal working pressure ≥8 MPa as the criterion for classifying high-pressure cylinders. The TSG 23-201X standard sets the threshold for high-pressure cylinders at ≥10 MPa.

[0003] With the development of navigation, aviation, and spacecraft, there is a need for lightweight, high-pressure, low-cost, and safe high-pressure oxygen cylinders. Currently, new energy technology offers hydrogen cylinders made of carbon fiber with a pressure of up to 70 MPa, but these cannot be used directly as oxygen cylinders because oxygen cylinders have an oxidizing effect on the polymer layers (such as polyethylene).

[0004] Publication No.: CN115076591B A stainless steel Type II gas cylinder and its manufacturing method are disclosed. The typical manufacturing method of the Type II gas cylinder is as follows: First, a seamless cylinder body is manufactured based on 301 series stainless steel material, with both ends tapered to form a spherical shell at both ends and a cylindrical shell in the middle of the metal cylinder body with equal thickness. Then, high-pressure expansion is performed in a cryogenic environment, preferably liquid nitrogen, and an external mold is used to constrain the cylindrical section of the stainless steel cylinder body. The expansion range is preferably 10-15% increase in the diameter of the cylindrical section. Third, the expanded stainless steel cylinder body is further strengthened by heat aging at 430℃ for 8 hours. Fourth, high-strength unidirectional fiber-reinforced composite material is circumferentially wound around the cylindrical section of the stainless steel cylinder body and cured. Finally, water pressure pre-tightening expansion is performed at room temperature to obtain the final product. However, this technical solution uses traditional hot tapping or spinning processes to form the cylinder shoulder, which is prone to defects such as cracks and wrinkles, resulting in poor forming quality and requiring increased wall thickness, which is not conducive to lightweighting. Furthermore, the purpose of the single cryogenic expansion is to increase strength, with the diameter increasing by 10-15%.

[0005] Therefore, there is an urgent need to design a gas cylinder for filling high-pressure oxygen and its manufacturing method to solve the problems of poor forming quality, low reliability and limited lightweighting of traditional spinning processes. Summary of the Invention

[0006] In view of this, the present invention aims to provide a gas cylinder for filling high-pressure oxygen and its manufacturing method, so as to solve the problems of poor forming quality, low reliability and limited lightweighting of traditional spinning process.

[0007] Conventional gas cylinder production often employs spinning, a process that uses a rotating tube blank and localized pressure applied by a spinning wheel to gradually shape the cylinder shoulder and bottom curved surfaces. This method is widely used in the manufacture of high-pressure gas cylinders made of aluminum alloy or stainless steel. However, this process has significant technical drawbacks: during spinning, the metal undergoes severe localized plastic deformation, making it highly susceptible to forming defects such as initial cracks and wrinkles in the cylinder shoulder area. If hot spinning is used to reduce deformation resistance, the rapid thermal conductivity of aluminum alloys leads to overall softening of the cylinder, or localized heating of stainless steel causes grain coarsening and residual stress concentration, severely affecting the uniformity of material properties. Cold spinning, on the other hand, faces the problem of rapid work hardening and a high risk of cracking. These defects not only reduce forming quality and yield but also become sources of fatigue cracks during subsequent hydraulic bulging and service life, forcing designers to increase the cylinder shoulder wall thickness to improve fatigue life. This results in increased cylinder weight and decreased specific strength, violating the goal of lightweight design.

[0008] To address the aforementioned issues, this application proposes an innovative manufacturing method combining diffusion welding and multiple hydraulic bulging, completely abandoning the traditional spinning and sealing process. By implementing multiple hydraulic bulging processes under mold constraints, supplemented by intermediate annealing, the metal billet achieves uniform overall expansion with a smooth stress distribution, avoiding cracks and wrinkles caused by large local deformations, resulting in a smooth, defect-free formed surface. The entire process is carried out at room temperature without heating, effectively preserving the original mechanical properties of the material, making it particularly suitable for heat-sensitive materials such as stainless steel. Simultaneously, solid-phase diffusion welding is used to connect the gas cylinder joints, forming a high-quality metallurgical bond without fusion zones or heat-affected zones, significantly improving joint strength and sealing performance. This technical approach not only achieves high-precision forming of cylinders with equal or optimized variable wall thickness, significantly reducing weight, but also significantly improves process stability and yield, solving long-standing problems such as poor forming quality, low reliability, and limited lightweighting in traditional spinning processes. It provides an advanced, reliable, and mass-producible new solution for the manufacturing of high-performance high-pressure oxygen cylinders.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows: One objective of this invention is to disclose a thin-walled stainless steel inner liner for filling high-pressure oxygen cylinders, with cylinder connectors at both ends, wherein the thin-walled stainless steel inner liner is formed by connecting the cylinder connectors to thin-walled seamless steel pipes through diffusion welding. The inner surface of the thin-walled stainless steel inner liner is provided with a PTFE bottle lining coating. The outer surface of the thin-walled stainless steel inner liner is sequentially provided with the polymer layer, the reinforcing winding layer, and the outer protective layer.

[0010] Furthermore, the thin-walled seamless steel pipe is connected to the gas cylinder connector by diffusion welding, with no fusion zone at the welding interface, forming a metallurgical bond.

[0011] Furthermore, the thin-walled seamless steel pipe and the gas cylinder connector are made of stainless steel.

[0012] Furthermore, the PTFE bottle liner coating includes: The nickel-iron-PTFE composite intermediate coating is electroplated onto the surface of the thin-walled stainless steel inner liner, with a thickness of 20±7μm. The PTFE coating applied to the surface of the composite intermediate layer is formed by ultrasonic electrostatic spraying of PTFE dispersion followed by drying and sintering.

[0013] Furthermore, the polymer layer is a polyethylene layer, which is formed on the outer surface of the thin-walled stainless steel inner liner by injection molding.

[0014] Furthermore, the reinforcing winding layer is formed using a full winding process that combines circumferential and longitudinal directions, and the main load-bearing structure is composed of carbon fiber composite material.

[0015] Furthermore, the outer protective layer includes: A glass fiber buffer layer covering the outside of the reinforcing winding layer; An epoxy resin protective layer covering the outside of the glass fiber buffer layer.

[0016] Another object of the present invention discloses a method for manufacturing a gas cylinder for filling high-pressure oxygen, based on any of the above-described gas cylinders for filling high-pressure oxygen, comprising the following specific steps: S1: The thin-walled seamless steel pipe is connected to the gas cylinder connector by diffusion welding to form an inner liner blank; S2: The inner liner blank is subjected to at least two water pressure expansions, and annealing is performed after each expansion to finally form the thin-walled stainless steel inner liner with the gas cylinder connectors at both ends. S3: Electroplating a nickel-iron-PTFE composite intermediate layer on the inner surface of the thin-walled stainless steel inner liner, and spraying sintered PTFE to form an inner lining coating. S4: The polymer layer, the reinforcing winding layer, and the outer protective layer are sequentially formed on the outer surface of the thin-walled stainless steel inner liner.

[0017] Furthermore, in step S1, the diffusion bonding process includes: S11: Mechanical grinding and chemical cleaning of the welded joint surfaces; S12: In a protective atmosphere with argon purity ≥99.99% and oxygen content <50ppm, assemble the gas cylinder connector, the thin-walled seamless steel pipe and the annular welding mold; S13: Heat to 840~980℃, pressurize to 12~15MPa, and hold for 20~30 minutes; S14: After slow cooling, anneal at 650℃ for 2 hours.

[0018] Furthermore, in step S2, the at least two water pressure bulging processes include N bulging processes and N-1 annealing and softening processes; each bulging process is achieved by internal water pressure under the constraint of the mold, and the water pressure range is 20~50MPa.

[0019] Compared with the prior art, the present invention provides a gas cylinder for filling high-pressure oxygen and its manufacturing method, which has the following advantages: 1. This invention achieves solid-phase metallurgical bonding between thin-walled seamless stainless steel pipes and gas cylinder joints by employing diffusion welding technology under high temperature, high pressure, and high-purity argon protection. This effectively avoids problems such as heat-affected zone embrittlement, cracking, and residual stress concentration caused by fusion welding, significantly improving the strength, sealing performance, and fatigue reliability of the joint. It solves the technical problems of easy leakage and short lifespan of traditional welding or threaded connections in high-pressure oxygen environments, thus achieving a breakthrough in high-reliability connection of gas cylinder liner.

[0020] 2. This invention combines multiple water pressure bulging and intermediate annealing softening processes, and uses multi-stage molds to control the bulging path step by step, to achieve high-precision plastic forming of thin-walled stainless steel inner liners from straight tubes to complex curved surfaces with bottle heads. This effectively avoids local thinning, wrinkling, or cracking caused by single large deformation. At the same time, by controlling unequal wall thickness to optimize the stress distribution of the bottle shoulder and body, it significantly improves the overall structural uniformity and pressure bearing capacity of the gas cylinder, solving the bottleneck problems of initial defects and low fatigue life caused by traditional spinning or necking processes.

[0021] 3. This invention provides a systematic manufacturing method for lightweight high-pressure oxygen cylinders. Through a multi-layer composite structure design of stainless steel inner liner + PTFE anti-oxidation lining + carbon fiber fully wound reinforcement, it fully leverages the sealing performance of the metal inner liner, the oxygen corrosion resistance of the polymer coating, and the high specific strength of the composite material. By integrating mature processes, it achieves a balance between high performance and low cost, and features lightweight, high burst pressure, and good safety. It has broad prospects for industrial application in high-end fields such as navigation, aviation, and aerospace. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of diffusion welding on the inner liner blank of the present invention; Figure 2 This is a schematic diagram of the first high-pressure water expansion forming of the bottle according to the present invention; Figure 3 This is a second schematic diagram of the high-pressure water expansion forming of the bottle of the present invention; Figure 4 For the present invention Figure 3 A magnified view of part A; Figure 5 This is a schematic diagram of the high-pressure oxygen cylinder structure of the present invention.

[0023] Explanation of reference numerals in the attached figures: 1. Thin-walled seamless steel pipe; 2. Gas cylinder connector; 201. Gas cylinder thread; 202. Sealing section; 3. Welding mold; 4. Temperature control coil; 5. Inner liner blank; 6. Interface; 7. Threaded plug; 8. Fluororubber sealing ring; 9. First bulging mold; 10. Second bulging mold; 11. Vent hole; 12. Inner cavity curved surface; 13. Third bulging mold; 14. Fourth bulging mold; 15. First inner liner blank; 16. Hydraulic pressure zone; 17. Expansion space; 18. Thin-walled stainless steel inner liner; 19. Polymer layer; 20. Reinforcing winding layer. Detailed Implementation

[0024] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0025] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0026] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] PTFE, polytetrafluoroethylene, commonly known as Teflon.

[0029] like Figures 1-5 As shown, the present invention provides a gas cylinder for filling high-pressure oxygen. The gas cylinder is composed of a thin-walled stainless steel inner liner 18 with gas cylinder connectors 2 at both ends, a Teflon (PTFE) inner lining coating, a polymer layer 19, a reinforcing winding layer 20, and an outer protective layer. The thin-walled stainless steel inner liner 18 is formed by connecting a thin-walled seamless steel pipe 1 to the gas cylinder connector 2 through diffusion welding, and then forming it through multiple hydraulic expansion processes. The curved surface of the cylinder shoulder or bottom is formed by expanding the metal layer by layer under the constraint of the mold driven by high pressure liquid. The material maintains a uniform and dense austenitic structure inside, without fusion zone or heat-affected zone.

[0030] By combining diffusion welding with multiple hydraulic bulging processes, a lightweight high-pressure oxygen cylinder with high sealing performance, high strength, and excellent resistance to oxygen corrosion is manufactured. This meets the stringent requirements of aviation, marine, and aerospace industries for high-pressure oxygen storage containers. It completely overcomes the technical difficulties such as "local thinning, wrinkling, and cracking" caused by the poor thermal conductivity and high deformation resistance of stainless steel in traditional hot-sealing or spinning processes. It also avoids defects such as porosity, cracks, and intergranular corrosion that may occur during fusion welding, ensuring the long-term safety and service reliability of the cylinder as a high-pressure oxygen container.

[0031] This design utilizes multiple hydraulic bulging processes, with step-by-step mold constraints and intermediate annealing softening, to achieve high-precision plastic forming of thin-walled stainless steel tubes from straight pipes to complex curved surfaces. This significantly improves the material's forming limit and avoids the risk of failure caused by single large deformations. Diffusion welding is completed in the solid state, resulting in a weld interface without molten pools or solidification segregation, forming a continuous metallurgical bond with high joint strength and excellent sealing. The Teflon (PTFE) lining effectively isolates high-pressure oxygen from contact with the metal, preventing oxidation and corrosion. The fully wrapped carbon fiber layer provides the main load-bearing support, achieving a balance between lightweight and high specific strength. The overall structure combines the sealing performance of metal gas cylinders with the lightweight and high-strength characteristics of composite material gas cylinders, overcoming the technical bottlenecks of low efficiency in traditional Type II gas cylinder structures and high cost in Type III gas cylinders.

[0032] Preferably, the thin-walled seamless steel pipe 1 and the gas cylinder connector 2 are made of 1Cr18Ni9Ti.

[0033] 1Cr18Ni9Ti is a typical austenitic stainless steel with good recrystallization ability and atomic diffusion activity. Under high temperature and pressure, it easily achieves interfacial atomic interdiffusion, promoting metallurgical bonding. The material has a moderate coefficient of thermal expansion, good compatibility with molds, and reduces thermal stress mismatch during welding. The titanium element inhibits carbide precipitation, preventing weakening or cracking of the weld interface due to carbon migration. Its austenitic structure has high stability and is not easily induced by martensitic transformation during room temperature plastic deformation, maintaining good plasticity and supporting large deformation amounts. The bulging rate can reach over 230%, even up to 700%, meeting the forming requirements from straight pipes to complex curved surfaces. It supports multiple hydraulic bulging processes and has no catalytic oxidation effect from high-pressure oxygen, avoiding the risk of combustion or explosion like carbon steel, resulting in high reliability.

[0034] Specifically, the PTFE bottle liner coating includes: The nickel-iron-PTFE composite intermediate coating is electroplated onto the surface of the stainless steel inner liner, with a thickness of 20±7μm. The PTFE coating applied to the surface of the composite intermediate layer is formed by ultrasonic electrostatic spraying of PTFE dispersion followed by drying and sintering.

[0035] The inner wall of the stainless steel liner is polished, cleaned, and acid-pickled to remove oxide layers and oil stains, exposing the active metal surface and improving coating adhesion. A composite electroplating process is used to deposit a nickel-iron alloy layer containing PTFE particles on the inner wall as a transition layer, possessing both metal bonding strength and self-lubricating properties. This enhances the interfacial bonding between the substrate and the PTFE coating, significantly improving the adhesion and peel resistance of the PTFE coating and preventing delamination during use. Using ultrasonic atomization and electrostatic adsorption technology, the PTFE dispersion is uniformly sprayed onto the composite coating surface, ensuring controllable coating thickness and uniform distribution, avoiding missed areas or accumulation, improving yield, and achieving thin, uniform, and drip-free fine coating, especially suitable for long cylindrical inner walls. The solvent is then removed by low-temperature drying at 80℃, followed by sintering at 370℃ to melt, level, and cross-link the PTFE particles, forming a dense and continuous film. This results in a smooth, non-porous, and chemically inert final protective layer that effectively isolates oxygen from metal contact.

[0036] This design solves the industry problem of easy corrosion and coating peeling of metal liner in high-pressure oxygen environments.

[0037] Specifically, the polymer layer 19 can be a polyethylene layer, which is formed on the outer surface of the stainless steel inner liner through injection molding.

[0038] Polyethylene, being an electrically inert material, can block the electrochemical pathway between the stainless steel inner liner and the carbon fiber (conductive), preventing galvanic corrosion in humid environments and improving the overall corrosion resistance of the gas cylinder. In its molten state, polyethylene is tightly wrapped around the surface of the stainless steel inner liner through injection molding. After cooling, it forms a mechanical interlocking structure, significantly improving the bond strength between the inner liner and the outer composite material. The injection molding process creates a continuous and dense coating layer that seals micropores or weld gaps on the inner liner surface, further enhancing the gas cylinder's airtightness.

[0039] This feature is injection molded onto the outer surface of the stainless steel inner liner and has multiple functions including cushioning, bonding, insulation, and sealing, significantly improving the structural integrity, environmental adaptability, and service life of the high-pressure oxygen cylinder.

[0040] Preferably, the polymer layer 19 has a thickness of 1.0~2.0 mm and a smooth surface, which is conducive to subsequent carbon fiber winding and bonding.

[0041] Preferably, the injection molding process can achieve local thickening or structural transition through mold design to meet the covering needs of complex curved areas such as bottle shoulders and bottle bottoms.

[0042] Preferably, in addition to polyethylene, the polymer layer 19 can also be made of polypropylene, nylon, PPS, TPU, EVA or PEEK, etc., depending on the actual application requirements.

[0043] Specifically, the carbon fiber reinforced winding layer 20 is formed by a full winding process that combines circumferential and longitudinal directions, and the main load-bearing structure is composed of carbon fiber composite materials.

[0044] In operation, high-pressure gas cylinders primarily bear circumferential tensile stress caused by internal pressure, approximately twice the magnitude of the axial stress. Through circumferential winding at approximately ±55°, carbon fibers are arranged along the direction of maximum stress, fully utilizing their high specific strength and high specific modulus to effectively resist the risk of bursting. 0° longitudinal winding (axial winding) supplements the axial strength of the cylinder, preventing axial cracking or buckling instability under pressure cycling or external loads, thus improving overall structural integrity. The circumferential and longitudinal fibers work synergistically to form an omnidirectional load-bearing composite shell, making the carbon fiber layer the primary structural layer bearing the internal pressure and significantly reducing the load on the metal liner. The fully wound structure evenly distributes the internal pressure load throughout the entire composite layer, avoiding localized stress concentration and improving fatigue life and safety.

[0045] This design, through a fully wrapped process combining circumferential and longitudinal directions, makes carbon fiber composite material the main load-bearing structure of the gas cylinder, significantly improving the specific strength, pressure resistance, and fatigue life of the gas cylinder, and achieving significant weight reduction.

[0046] Preferably, the full winding process can optimize the mechanical properties of different pressure levels and structural areas (such as bottle shoulders and cylinders) by adjusting parameters such as winding angle, number of layers, and tension. Furthermore, the use of fully automated fiber winding equipment can precisely control the fiber direction and tension, resulting in good repeatability and stable quality in mass production.

[0047] Specifically, the outer protective layer includes: A glass fiber buffer layer covering the outside of the carbon fiber reinforced winding layer 20; An epoxy resin protective layer covering the outside of the glass fiber buffer layer.

[0048] On the outer surface of the gas cylinder that has been fully wrapped with carbon fiber, a layer of fiberglass cloth is manually or mechanically wrapped, with a width matching the cylinder body and uniform tension, covering the entire wrapped area to form a fiberglass buffer layer; a layer of epoxy resin coating is brushed or sprayed to impregnate the fiberglass layer and cured at room temperature or under heating conditions to form a dense and smooth epoxy resin protective layer; after curing, the surface is sanded and visually inspected to ensure that the coating is continuous, free of bubbles and scratches.

[0049] The glass fiber buffer layer, acting as an intermediate buffer layer, absorbs external impact energy, preventing direct damage to the carbon fiber layer while enhancing the adhesion of the epoxy resin layer. This design significantly improves the gas cylinder's impact and abrasion resistance, preventing carbon fiber breakage or delamination due to localized impacts and extending its service life.

[0050] The epoxy resin protective layer forms a dense outer surface, isolating it from environmental corrosion such as moisture, ultraviolet rays, and salt spray, while providing a good appearance and marking base. This coating exhibits excellent weather resistance, chemical corrosion resistance, and anti-aging properties, making it suitable for complex service environments such as marine, high-altitude, and extremely cold regions. The surface can be coated with markings and barcodes for easy management and traceability.

[0051] The dual-layer structure design of glass fiber buffer layer + epoxy resin protective layer effectively improves the environmental adaptability, mechanical durability and safety of use of high-pressure oxygen cylinders.

[0052] Preferably, the total thickness of the two layers is typically 0.3~0.8mm, which adds very little weight and does not affect the overall lightweight advantage.

[0053] This invention provides a method for manufacturing a gas cylinder for filling high-pressure oxygen, comprising the following steps: S1: Diffusion welding forms the inner liner blank 5 A 1Cr18Ni9Ti stainless steel seamless pipe with a wall thickness of 0.8mm and an outer diameter of 120mm is selected as the inner liner material. The cylinder connector 2 is made of the same material and has a cylinder thread 201 and a sealing section 202 at its end. The cylinder thread 201 is used to connect to external valves or interfaces, while the sealing section 202 ensures the sealing performance of the cylinder under high pressure. The cylinder connector 2 is cylindrical and made of the same 1Cr18Ni9Ti stainless steel material as the thin-walled seamless steel pipe 1 to ensure the quality of the metallurgical bond after welding.

[0054] The weld joint surfaces are mechanically sanded with sandpaper of 800 grit or higher, and then ultrasonically cleaned with acetone and alcohol to remove oxide film and oil.

[0055] Before diffusion welding, the gas cylinder connector 2 is cooled in liquid nitrogen to a temperature of -196°C, causing it to shrink. Simultaneously, the thin-walled seamless steel pipe 1 and the welding mold 3 can be made of H13 hot work die steel, heated to 1000–1500°C, preferably 1200°C. This hot-cold assembly strategy helps reduce residual stress generated during welding and improves the metallurgical bonding quality of the joint.

[0056] In a high-purity argon protective environment, with argon purity ≥99.99% and oxygen content <50ppm, the cooled gas cylinder connector 2 is inserted into both ends of the thin-walled seamless steel pipe 1, and the welding mold 3 is fitted on. After assembly, the temperature is controlled by the temperature control coil 4.

[0057] The assembly temperature is gradually controlled to 840–980℃, preferably 900℃, while applying a pressure of 13–15 MPa, preferably 13 MPa, and holding for 20–25 minutes, preferably 25 minutes. After holding, it is slowly cooled to 300℃ at a rate of ≤5℃ / min, then air-cooled, and finally annealed at 650℃ for 2 hours. Metallographic testing confirms the disappearance of the weld interface, and the shear strength test result is ≥500 MPa, forming a complete inner liner blank 5.

[0058] This diffusion welding process is completed in the solid state, avoiding the problems of heat-affected zone embrittlement, intergranular corrosion and residual stress concentration caused by fusion welding. The metal fibers in the weld zone are continuous and there is no fusion line. The joint has high strength and good sealing performance, making it suitable for long-term service in high-pressure oxygen environments.

[0059] S2: Multiple water pressure bulging and intermediate annealing One end of the inner liner blank 5 is sealed with a threaded plug 7 and a fluororubber sealing ring 8, and the other end is connected to the water press interface 6 to form a closed water pressure zone 16.

[0060] The first expansion mold 9 on one side of the first group and the second expansion mold 10 on the other side of the first group are set externally to perform the first water pressure expansion on the cylinder part. The water pressure is raised to 30MPa and held for 10 minutes to make the inner liner initially expand and form the first inner liner blank 15.

[0061] The first forming mold 9 and the second forming mold 10 have internal curved surfaces 12 to constrain and guide the plastic deformation of the thin-walled seamless steel pipe 1 under water pressure, so that it is gradually and precisely formed into the complex curved surface contour required by the design, such as the shoulder of a bottle. The side walls of the first forming mold 9 and / or the second forming mold 10 are provided with vent holes 11 to allow gas to be discharged between the thin-walled seamless steel pipe 1 and the first forming mold 9, and between the thin-walled seamless steel pipe 1 and the second forming mold 10 during deformation.

[0062] After bulging, the workpiece is removed and annealed at 850℃ for 1 hour to eliminate residual stress and restore the material's plasticity.

[0063] Then, the third bulging mold 13 and the fourth bulging mold 14 of the second group are replaced. An expansion space 17 is reserved between the mold and the workpiece for the second water pressure bulging. The water pressure is increased to 40MPa, so that the inner liner expands further under the action of the water pressure zone 16 and fits the mold cavity.

[0064] A third hydraulic bulging process can also be performed as needed: replace the third set of bulging molds, increase the water pressure to 50MPa, and hold the pressure for 10 minutes to fully form the inner liner and achieve the complex curved surface contour required by the design. Furthermore, based on existing technology, the number of bulging cycles can be increased, and appropriate processing parameters can be selected to significantly improve the bulging rate.

[0065] After each expansion, an annealing treatment is performed at 850℃ for 1 hour to eliminate residual stress and restore the material's plasticity. This ultimately results in a thin-walled stainless steel inner liner 18 with gas cylinder connectors 2 at both ends. The expansion ratio at the bottle shoulder is lower than that of the bottle body, achieving an optimized design with unequal wall thickness. The wall thickness in key areas is controlled between 0.6 and 0.8 mm to meet the requirements for uniform stress distribution.

[0066] This multi-stage hydraulic bulging process effectively controls the deformation amount in each pass through a step-by-step loading and intermediate annealing strategy, avoiding localized thinning or cracking of thin-walled stainless steel tubes caused by large one-time deformation. Mold constraints ensure that the bottle shoulder and body are formed synchronously, resulting in a smooth, wrinkle-free curved surface. Annealing restores the material's plasticity, ensuring the stability of subsequent forming. Compared to traditional single-stage bulging, this process significantly improves forming quality and yield, with bulging rates reaching over 230%, and even as high as 700%.

[0067] S3: Inner surface treatment forms a PTFE antioxidant lining. After activating the inner surface of the thin-walled stainless steel inner liner 18, a nickel-iron-PTFE composite intermediate coating is first electroplated with a thickness of 20±7μm to enhance the adhesion between the PTFE coating and the metal substrate.

[0068] PTFE dispersion is applied using an ultrasonic electrostatic spraying process to ensure uniform adhesion of the coating to the inner wall.

[0069] The base solution is dried at 80℃±5℃ for 25-35 minutes to evaporate; then sintered at 370℃±5℃ for 13-14 minutes to form a dense, continuous Teflon (PTFE) lining coating with a total thickness of 30-50 μm. This thickness range effectively isolates oxygen from metal without significantly increasing the weight of the gas cylinder.

[0070] This PTFE liner has excellent chemical inertness and resistance to oxygen corrosion, effectively isolating high-pressure oxygen from direct contact with the stainless steel substrate, preventing metal oxidation and ion precipitation, and ensuring oxygen purity. It is particularly suitable for storing medical and aerospace-grade high-purity oxygen.

[0071] S4: Outer composite structure molding A 1.5mm thick polyethylene layer is formed on the outer surface of the thin-walled stainless steel inner liner 18 using injection molding process. This serves as a buffer and adhesive layer, mitigating the thermal expansion differences between the metal and the composite material and improving the stability of the interface bonding.

[0072] A full winding process combining circumferential (±55°) and longitudinal (0°) winding is used on the outer surface of the polyethylene layer to wind epoxy resin-based T700 carbon fiber, forming an 8mm thick reinforcing winding layer 20. The main load-bearing structure is composed of carbon fiber composite material, which bears the main circumferential tensile stress and significantly improves the specific strength of the gas cylinder.

[0073] A glass fiber buffer layer and an epoxy resin coating are sequentially wrapped around the outside of the reinforcing winding layer 20 to form an external protective layer, which prevents mechanical damage, ultraviolet aging and environmental corrosion, and improves the overall durability of the gas cylinder.

[0074] Final product performance testing The performance of the finished gas cylinders was tested, and the results are as follows: Burst pressure: >25MPa (actually measured 28MPa), meets design requirements; Weight: 15% lighter than the same type III aluminum alloy gas cylinder, achieving weight reduction; Fatigue life: More than 12,000 cycles under 30MPa pressure without leakage; Oxygen purity retention: After long-term oxygen filling and discharging tests, no metal ions were released, which meets the GB 8982-2009 standard for "Medical and Aviation Respiratory Oxygen". Sealing performance: Helium mass spectrometry leak detection ≤1×10-9 Pa·m³ / s, meeting aerospace-grade sealing requirements; Corrosion resistance: No corrosion spots were observed after 500 hours of salt spray testing, and the PTFE lining remained undamaged.

[0075] In summary, this invention successfully manufactures a lightweight, high-strength, and oxygen-corrosion-resistant high-pressure oxygen cylinder through the systematic integration of processes such as diffusion welding, multiple hydrostatic bulging, PTFE lining, and carbon fiber full winding. This cylinder combines high reliability with low cost, and has broad application prospects in the maritime, aviation, and aerospace fields.

[0076] Other existing technologies were used in the processing, which will not be described in detail here.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gas cylinder for filling with high pressure oxygen, characterized by, A thin-wall stainless steel liner (18) with cylinder joint (2) at both ends, said thin-wall stainless steel liner (18) is formed by diffusion welding of thin-wall seamless steel pipe (1) and said cylinder joint (2); The inner surface of said thin-wall stainless steel liner (18) is provided with PTFE bottle body lining plating layer; The outer surface of said thin-wall stainless steel liner (18) is sequentially provided with high polymer polymer layer (19), reinforced winding layer (20) and external protection layer.

2. The gas cylinder for filling high pressure oxygen according to claim 1, wherein Said thin-wall seamless steel pipe (1) and said cylinder joint (2) are connected by diffusion welding, and there is no fusion zone at the welding interface, forming metallurgical bonding.

3. The gas cylinder for filling high pressure oxygen according to claim 2, wherein The material of said thin-wall seamless steel pipe (1) and said cylinder joint (2) is stainless steel.

4. The cylinder for filling high pressure oxygen gas as claimed in claim 1 wherein, Said PTFE bottle body lining plating layer comprises: Nickel-iron-PTFE composite intermediate plating layer deposited on the surface of said thin-wall stainless steel liner (18), with a thickness of 20±7μm; PTFE coating on the surface of the composite intermediate plating layer, formed by ultrasonic electrostatic spraying of PTFE dispersion liquid and then drying and sintering.

5. The cylinder for filling high pressure oxygen gas as claimed in claim 1 wherein, Said high polymer polymer layer (19) is a polyethylene layer formed on the outer surface of said thin-wall stainless steel liner (18) by injection molding process.

6. The cylinder for filling high pressure oxygen gas as claimed in claim 1 wherein, Said reinforced winding layer (20) is formed by full winding process combining hoop and longitudinal directions, and the main load-bearing structure is composed of carbon fiber composite material.

7. The cylinder for filling high pressure oxygen gas as claimed in claim 1 wherein, Said external protection layer comprises: Glass fiber buffer layer coated on the outside of said reinforced winding layer (20); Epoxy resin protection layer coated on the outside of the glass fiber buffer layer.

8. A method of manufacturing a gas cylinder for filling with high-pressure oxygen, characterized by, The filling high-pressure oxygen cylinder based on any one of claims 1-7, comprising the following specific steps: S1: connecting said thin-wall seamless steel pipe (1) and said cylinder joint (2) by diffusion welding to form a liner blank (5); S2: performing water pressure bulging on said liner blank (5) at least twice, and annealing after each bulging to finally form said thin-wall stainless steel liner (18) with said cylinder joint (2) at both ends; S3: electroplating nickel-iron-PTFE composite intermediate plating layer on the inner surface of said thin-wall stainless steel liner (18), and spraying and sintering PTFE to form the lining plating layer; S4: sequentially forming said high polymer polymer layer (19), said reinforced winding layer (20) and external protection layer on the outer surface of said thin-wall stainless steel liner (18).

9. The method of manufacturing a high-pressure oxygen gas cylinder according to claim 8, wherein In step S1, the diffusion welding process comprises: S11: mechanical polishing and chemical cleaning of the welding joint surface; S12: assembling said cylinder joint (2), said thin-wall seamless steel pipe (1) and ring-shaped welding mold (3) in a protective atmosphere with argon purity ≥99.99% and oxygen content <50ppm; S13: heating to 840~980℃, pressurizing to 12~15MPa, and holding for 20~30 minutes; S14: slow cooling and then annealing at 650℃ for 2 hours.

10. The method of manufacturing a high-pressure oxygen gas cylinder according to claim 8, wherein In step S2, the at least two water pressure bulging includes N times of bulging and N-1 times of annealing softening; each bulging is realized by internal water pressure under the constraint of the mold, and the water pressure pressure range is 20~50MPa.

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