A thin-walled metal liner for a variable thickness cryogenic storage tank

Abstract

This invention belongs to the field of aerospace technology and discloses a thin-walled metal liner for a cryogenic tank with variable thickness. It mainly consists of a cylindrical metal liner section and a hemispherical metal liner bottom, connected together. Based on the actual stress distribution during the tank's service life, it is spirally rolled from metal strips of varying thickness and uniform width. The hemispherical metal liner bottom is made of sheet metal of corresponding thickness, selected according to the thickness distribution at the ends of the cylindrical metal liner section, and prepared by spinning or stamping. A through-hole is pre-drilled at the top of the hemispherical metal liner bottom, which is connected to the cylindrical metal liner section by welding or flange connection. The cylindrical metal liner section has a circumferential and / or axial variable thickness distribution; the thickness is increased in critical stress areas and reduced in non-critical areas. This invention can significantly reduce the equivalent areal density of the tank, thereby improving the aircraft's carrying capacity, helping to extend the tank's service life, reducing fatigue damage, and improving its reliability during long-term service.

Description

Technical Field

[0001] This invention relates to the field of aerospace technology, and in particular to a thin-walled metal liner for a variable-thickness cryogenic tank. Background Technology

[0002] As a key component of the propulsion and structural systems of spacecraft, the lightweighting level of cryogenic tanks determines the main performance indicators of the launch vehicle. The article "Chen Zhenguo, Jiao Weicheng, Yan Meiling, et al. Research progress on the leakage resistance of carbon fiber reinforced resin matrix composite cryogenic tanks [J]. Fiberglass / Composite Materials, 2018(11):109-116" points out that, taking expendable launch vehicles as an example, the tank mass accounts for more than 50% of the total mass of the launch vehicle, indicating a huge potential for lightweighting. For next-generation spaceplanes, the lightweighting requirements are even more stringent. For example, such tanks require an equivalent areal density of no more than 9 kg / m³. 2 When manufacturing the tank body using aluminum alloy, the equivalent thickness cannot exceed 3.3 mm, the aspect ratio must be greater than 1000, the pressure resistance must be no less than 0.5 MPa, and the yield strength of the tank material must be no less than 325 MPa. These requirements exceed the performance specifications of existing aluminum alloys, including advanced aluminum-lithium alloys. Furthermore, this ultra-large aspect ratio thin-walled metal structure has poor overall rigidity and is extremely difficult to manufacture. Therefore, traditional metal tanks can no longer meet the requirements of next-generation spaceplanes.

[0003] Using composite materials is one of the important ways to achieve lightweight storage tanks. However, due to the compatibility problem between composite materials and liquid oxygen, the resin matrix in the composite material will crack or develop pores at low temperatures, posing a risk of microcracks and liquid leakage to the liquid oxygen storage tank. The patent "A Method for Molding a Large-Size Ultra-Lightweight Cryogenic Storage Tank" (application number: 202310675618.7) proposes a method for molding a cryogenic storage tank that combines a metal inner liner with a composite outer shell. The cylindrical section of the metal inner liner, as the sealing structure of the cryogenic storage tank, can be obtained by continuously rolling a thin metal strip into a spiral structure. During molding, only the rolling angle needs to be changed to prepare cylindrical sections of different diameters using the same width of thin metal strip. The method mentioned in this paper uses metal strip of uniform thickness for rolling the inner liner section. This is not an ideal solution for manufacturing ultra-large thin-shell metal cylindrical sections. The main problems are as follows: (1) The uniform thickness design of the cylindrical section leads to low material utilization efficiency in different areas of the tank. The critical stress area may be affected by insufficient thickness, which may affect the load-bearing capacity, while the non-critical area may be affected by excessive thickness, which may increase unnecessary weight. (2) During service, the uniform thickness tank is prone to stress concentration at the critical parts of the connection and support structure. This not only affects the fatigue life of the tank, but may also lead to structural failure. Especially under cyclic load, the uniform thickness design is difficult to effectively disperse stress, which increases the risk of tank failure. (3) Although the rolling of uniform thickness strip simplifies the initial manufacturing process, it often requires local thickening or thinning in subsequent processing to adapt to the load-bearing requirements of different areas. This additional processing step not only increases the complexity of manufacturing, but may also lead to increased costs and quality control problems.

[0004] To address the contradiction between structural weight and performance, fatigue caused by stress concentration, complexity and cost of subsequent processing, and low material utilization when using uniform thickness metal strip to roll metal inner cylinder sections, a new type of variable thickness thin-walled metal inner liner needs to be developed. Summary of the Invention

[0005] To improve the launch efficiency of spacecraft, meet stringent lightweight requirements, and ensure sealing performance, this invention provides a thin-walled metal liner for a variable-thickness cryogenic tank. This addresses the problems of low material utilization efficiency, poor fatigue resistance due to stress concentration, and high costs associated with complex subsequent processing of existing uniform-thickness metal liners. This provides a fundamental guarantee for the design and manufacturing of cryogenic tanks for next-generation spaceplanes, heavy-lift launch vehicles, and other advanced spacecraft.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A thin-walled metal liner for a variable-thickness cryogenic storage tank, comprising a metal liner 1; the metal liner 1 is mainly composed of a cylindrical metal liner section 3 and a hemispherical metal liner bottom 2 connected together; both ends of the metal liner section 3 are respectively connected to the hemispherical metal liner bottom 2; according to the actual stress distribution of the storage tank during service, it is spirally rolled from metal strip of variable thickness and equal width; the variable-thickness strip of the metal liner section 1 is rolled to form a curved seam, which, during the rolling process, causes the two sides to bite together. The edges interlock, and the varying thickness strip is pressed and secured by adjusting the relatively rolling engagement wheels in the rolling equipment. The hemispherical metal inner liner bottom 2 is made of a plate of corresponding thickness according to the thickness distribution at the end of the metal inner liner section 3, and is prepared by spinning or stamping. A through hole is reserved at the top of the hemispherical metal inner liner bottom 2, and it is connected to the metal inner liner section 3 by welding or flange connection. The metal inner liner section 3 has a circumferential and / or axial varying thickness distribution; the thickness is increased in the critical stress area and the wall thickness is reduced in the non-critical area.

[0007] In the circumferential and axial variable thickness distributions, the length of the spiral corresponding to each thickness region is determined based on the number of turns and the length of a single spiral turn.

[0008] The length of the single-turn spiral d is the diameter of the helix, and p is the pitch.

[0009] The thickness of the metal inner liner section 3 is increased at both ends where it connects to the bottom 2 of the hemispherical metal inner liner box, while the thickness of the middle part of the metal inner liner section 3 is reduced.

[0010] The variable thickness metal strip is made of aluminum alloy or stainless steel.

[0011] The variable thickness metal strip is produced by a continuous casting machine, heat-treated in a heating furnace, then rolled by a rolling mill according to the thickness distribution of the strip, and finally straightened by a straightener and cut and coiled by a flying shear to a coiler to obtain variable thickness strip coils.

[0012] The seam of the metal inner tube section 3 is sealed by using sealant.

[0013] The adhesive is a low-temperature environment sealant.

[0014] The beneficial effects of this invention are:

[0015] (1) The variable thickness thin-walled metal liner of the present invention, since the cylindrical section of the metal liner is formed by rolling variable thickness metal strip into a spiral structure, can optimize the structure for specific stress areas of the tank. By increasing the thickness of key parts, its load-bearing capacity can be improved, while reducing the thickness of non-critical parts to reduce the overall weight. It can significantly reduce the equivalent surface density of the tank, thereby improving the carrying efficiency of the aircraft.

[0016] (2) The variable thickness thin-walled metal liner of the present invention, wherein the cylindrical section of the metal liner is rolled from variable thickness strip, can effectively reduce stress concentration in the tank under cyclic loads, especially in critical parts of the connection and support structure. This helps to extend the service life of the tank, reduce fatigue damage, and improve its reliability in long-term service.

[0017] (3) The variable thickness thin-walled metal liner of the present invention uses cylindrical sections rolled from variable thickness metal strips, which can better match the actual stress distribution of the tank during service. For example, the thickness is increased in axial and circumferential stress concentration areas, while the thickness is reduced in areas with lower stress. This targeted design can improve the utilization efficiency of materials and enhance the overall performance of the structure.

[0018] (4) The variable thickness thin-walled metal liner of the present invention can reduce subsequent processing steps, such as local thickening or thinning, by rolling the variable thickness strip, thereby simplifying the manufacturing process and reducing production costs. At the same time, by adopting this specific forming technology, it can be ensured that the metal liner produced each time is consistent in terms of size, shape, and material distribution, thus ensuring the quality and performance stability of the storage tank. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the thin-walled metal inner liner of the variable thickness cryogenic storage tank in this invention;

[0020] Figure 2(a) is a schematic diagram of the material flow direction when the metal liner is subjected to internal pressure;

[0021] Figure 2(b) is a schematic diagram of the stress analysis of the cylinder wall section when the metal inner liner is subjected to internal pressure;

[0022] Figure 3(a) is a schematic diagram of the circumferential variable thickness distribution of the metal inner tube section of the present invention;

[0023] Figure 3(b) is the AA cross-sectional view of Figure 3(a);

[0024] Figure 3(c) shows the periodic variation of the circumferential wall thickness with the helix.

[0025] Figure 4 This is a schematic diagram of the axial variable thickness distribution of the metal inner liner section of the present invention;

[0026] Figure 5(a) is a schematic diagram of the local distribution of the wall thickness of the metal inner tube section of the present invention;

[0027] Figure 5(b) is a BB cross-sectional view of Figure 5(a);

[0028] Figure 5(c) is a CC cross-sectional view of Figure 5(a).

[0029] In the diagram, 1 represents the metal inner liner, 2 represents the bottom of the metal inner liner box, and 3 represents the section of the metal inner liner cylinder. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0031] A large-size, ultra-lightweight, non-uniform thickness cryogenic storage tank metal liner includes a metal liner 1. The metal liner 1 is composed of a cylindrical metal liner section 3 and a hemispherical metal liner bottom 2. The metal liner section 3 is spirally rolled from metal strip of varying thickness and uniform width according to the actual stress distribution of the storage tank during service. Both ends of the metal liner section 3 are connected to the hemispherical metal liner bottom 2. The variable thickness strip of the rolled metal liner section is rolled to form a curved seam. During the rolling process, the seam edges on both sides interlock. By adjusting the interlocking wheels that roll relative to each other in the rolling equipment, the seam of the variable thickness strip is pressed and secured. The hemispherical metal liner bottom 2 is made of a plate of corresponding thickness according to the thickness distribution at the end of the metal liner section 3. It is prepared by spinning or stamping. A through hole is reserved at the top of the bottom of the tank, and it is connected to the metal liner section 3 by welding or flange connection.

[0032] The variable thickness metal strip is made of aluminum alloy or stainless steel.

[0033] The variable thickness metal strip is produced by a continuous casting machine, heat-treated in a heating furnace, then rolled by a rolling mill according to the thickness distribution of the strip, and finally straightened by a straightener and cut and coiled by a flying shear to a coiler to obtain variable thickness strip coils.

[0034] The thickness distribution of each part of the metal liner 1 is determined according to the specific conditions of the storage tank during service, such as the stress situation when it is placed horizontally or vertically, and the stress distribution when the metal liner is subjected to internal pressure and constrained by the composite shell. The thickness should be increased in critical stress areas, while the wall thickness of the cylinder section in non-critical areas can be appropriately reduced.

[0035] The seam of the metal inner tube section 3 is sealed by using sealant.

[0036] The adhesive is one of the ultra-low temperature environment sealants such as polyimide sealant and polytetrafluoroethylene sealant.

[0037] Example 1: Combination Figure 1 This invention discloses a thin-walled metal liner for a variable-thickness cryogenic storage tank, comprising a metal liner 1. The metal liner 1 is composed of a cylindrical metal liner section 3 and a hemispherical metal liner bottom 2. The metal liner section 3 is spirally rolled from a metal strip of variable thickness and uniform width, according to the actual stress distribution during the service of the storage tank. Both ends of the metal liner section 3 are connected to the hemispherical metal liner bottom 2. The variable-thickness strip of the rolled metal liner section is rolled to form a curved seam. During the rolling process, the seam edges on both sides interlock. By adjusting the interlocking wheels that roll relative to each other in the rolling equipment, the seam of the variable-thickness strip is pressed and secured. The hemispherical metal liner bottom 2 is made of a plate of corresponding thickness according to the thickness distribution at the end of the metal liner section 3, and is prepared by spinning or stamping. A through hole is reserved at the top of the bottom, and it is connected to the metal liner section 3 by welding or flange connection.

[0038] Preferably, the variable thickness metal strip is produced by a continuous casting machine, heat-treated by a heating furnace, then rolled by a rolling mill according to the thickness distribution of the strip, and finally straightened by a straightener and cut and coiled by a flying shear to a coiler to obtain variable thickness strip coils.

[0039] Preferably, the thickness distribution of each part of the metal liner 1 is determined according to the specific conditions of the storage tank during service, such as the stress situation when it is placed horizontally or vertically, and the stress distribution when the metal liner is subjected to internal pressure and constrained by the composite shell. The thickness should be increased in the critical stress area, while the wall thickness of the cylinder section in the non-critical area can be appropriately reduced.

[0040] Preferably, the seam of the metal inner liner section 3 is sealed using a sealant bonding method. The adhesive is one of ultra-low temperature environment sealants, such as polyimide sealant or polytetrafluoroethylene sealant.

[0041] Example 2: The specific implementation of the present invention will be further described in conjunction with Figures 2(a) and 2(b). This invention proposes a thin-walled metal liner for a variable-thickness cryogenic storage tank, comprising a metal liner 1. The metal liner 1 is composed of a cylindrical metal liner section 3 and a hemispherical metal liner bottom 2. The metal liner section 3 is spirally rolled from a metal strip of variable thickness and uniform width, according to the actual stress distribution during the tank's service life. Both ends of the metal liner section 3 are connected to the hemispherical metal liner bottom 2. The variable-thickness strip used to roll the metal liner section is formed into a curved seam during rolling, allowing the seam edges to interlock. The seam is pressed and secured by adjusting the relatively rolling engagement wheels in the rolling equipment. The hemispherical metal liner bottom 2 is made from a plate of corresponding thickness based on the thickness distribution at the ends of the metal liner section 3, and is prepared by spinning or stamping. A through-hole is pre-drilled at the top of the bottom, and the bottom is connected to the metal liner section 3 by welding or flange connection. The stress analysis of the metal liner 1 under internal pressure and the constraint of the composite outer shell is as follows:

[0042] Due to the frictional force exerted on the outer wall of the metal inner liner by the inner wall of the composite outer shell, the following force balance equation can be obtained:

[0043] T B -μF N =T A

[0044] The circumferential stress at any point on the cylinder wall section is:

[0045]

[0046] During the compression process, the metal inner liner remains in close contact with the composite outer shell under internal pressure. The thickness stress on the inner and outer surfaces of the cylinder wall section is the same and is under pressure.

[0047] σ t =-p

[0048] According to the Mise yield criterion, the equivalent stress at a certain point in the cylinder wall section can be obtained as follows:

[0049]

[0050] In the formula F N denoted as Σ, where xi is the supporting reaction force on the metal inner liner section, xi is the distance from any point on the inner liner section to the transition point of the arc section, and μ is the coefficient of friction between the composite outer shell and the metal inner liner.

[0051] In this embodiment, theoretical analysis shows that when the metal inner liner is subjected to internal pressure and constrained by the composite outer shell, the equivalent stress is greatest at the transition point between the arc segment of the bottom of the box and the straight segment of the cylinder wall. The closer to the center point of the symmetry axis of the metal inner liner, the smaller the equivalent stress. Therefore, the thickness of the metal inner liner cylinder segment is increased at both ends of the bottom of the box, while the thickness of the middle part of the cylinder segment can be appropriately reduced.

[0052] Example 3: Combining Figure 3(a), Figure 3(b), Figure 3(c) and Figure 4 This invention discloses a thin-walled metal liner for a variable-thickness cryogenic storage tank, comprising a metal liner 1. The metal liner 1 is composed of a cylindrical metal liner section 3 and a hemispherical metal liner bottom 2. The metal liner section 3 is spirally rolled from a metal strip of variable thickness and uniform width, according to the actual stress distribution during the tank's service life. Both ends of the spiral section 3 are connected to the hemispherical metal liner bottom 2. The variable-thickness strip of the rolled metal liner section is rolled to form a curved seam, which interlocks during the rolling process. The seam is pressed and secured by adjusting the relatively rolling engagement wheels in the rolling equipment. The hemispherical metal liner bottom 2 is made of a plate of corresponding thickness according to the thickness distribution at the ends of the metal liner section 3, and is prepared by spinning or stamping. A through-hole is pre-drilled at the top of the bottom, and it is connected to the metal liner section 3 by welding or flange connection. An example of the variable thickness distribution of the metal liner section 3 is shown below.

[0053] (1) Circumferential thickness distribution of the metal inner liner section:

[0054] Using a variable thickness strip with an initial thickness of 1.5mm, a reduction thickness of 0.5mm, and a bandwidth of 137mm, a cylindrical section with a diameter of 500mm and a length of 500mm with varying thickness along the circumferential direction is rolled. The calculation formula for the helical length is as follows:

[0055]

[0056] In the formula, L is the length of one turn of the helix, d is the diameter of the helix, and p is the pitch. The thickness distribution of the strip is calculated as follows: Region I: thickness 1.5mm, length 2361.7mm; Region II: thickness 0.5mm, length 3149mm; Region III: length 2361.7mm.

[0057] In this embodiment, the wall thickness at both ends of the metal inner liner section is increased, while the wall thickness in the middle section is reduced. As can be seen from Embodiment 1, the equivalent stress is greatest at the transition point between the arc section at the bottom of the box and the straight section of the cylinder wall. The equivalent stress is smaller when it is closer to the center point of the axis of symmetry of the metal inner liner. Increasing the thickness in the stress concentration area and reducing the thickness in the area with less stress not only improves the material utilization efficiency but also enhances the overall performance of the entire structure.

[0058] (2) Axial varying thickness distribution of the metal inner liner section:

[0059] Using a variable thickness strip with an initial thickness of 1.5mm, a reduction thickness of 0.5mm, and a bandwidth of 137mm, a cylindrical section with a diameter of 500mm and a length of 500mm with axially varying thickness is rolled. The formula for calculating the helical length is as follows:

[0060]

[0061] In the formula, L is the length of one turn of the helix, d is the diameter of the helix, and p is the pitch. The thickness distribution of the strip is calculated as follows: Region I: thickness 1.5mm, length 3936.2mm; Region II: thickness 0.5mm, length 3936.2mm.

[0062] In this embodiment, the wall thickness gradually decreases from thick to thin along the axial direction starting from one end of the metal inner liner 1. When the tank is placed vertically or filled with cryogenic fuel, the downward-facing end of the metal inner liner 1 is affected by factors such as its own weight and the weight of the fuel, and has high load-bearing requirements. The design is optimized according to the specific stress area of ​​the tank, increasing the thickness of key parts to improve load-bearing capacity, while reducing the thickness of non-key parts, significantly reducing the overall weight of the tank.

[0063] (3) Local distribution of wall thickness in the metal inner liner section:

[0064] Referring to Figures 5(a), 5(b), and 5(c), a locally variable thickness cylindrical section with a diameter of 500 mm and a length of 500 mm is produced by rolling a variable thickness strip with an initial thickness of 1.5 mm, a reduction thickness of 0.5 mm, and a bandwidth of 137 mm. When the storage tank is equipped with connecting or supporting structures, the wall thickness distribution of the metal inner liner section 1 adopts a localized distribution based on theoretical calculations or simulation analysis.

[0065] The wall thickness distribution of the strip is set as follows: Region I: thickness 1.5mm, length 1968.1mm; Region II: thickness 0.5mm, length 1968.1mm; Region III: thickness 1.5mm, length 1968.1mm; Region IV: thickness 0.5mm, length 1968.1mm.

[0066] The localized wall thickness distribution of the metal inner tank section facilitates the subsequent addition of supporting structures within the metal inner tank, effectively reducing stress concentration under cyclic loads, especially in critical areas of the connection and support structures. This design extends the service life of the tank, reduces fatigue damage, and thus improves its reliability during long-term service.

Claims

1. A thin-walled metal liner for a variable-thickness cryogenic storage tank, characterized in that, The variable thickness cryogenic storage tank thin-walled metal liner includes a metal liner (1); the metal liner (1) is mainly composed of a cylindrical metal liner section (3) and a hemispherical metal liner bottom (2) connected together; the two ends of the metal liner section (3) are respectively connected to the hemispherical metal liner bottom (2); according to the actual stress distribution of the storage tank during service, it is spirally rolled from metal strips of variable thickness and equal width; the variable thickness strip of the metal liner section (3) is rolled to form a curved seam, so that the seam edges on both sides interlock during the rolling process, through By adjusting the meshing rollers that roll relative to each other in the rolling equipment, the tape of varying thickness is pressed and secured; the bottom of the hemispherical metal liner box (2) is made of a plate of corresponding thickness according to the thickness distribution at the end of the metal liner section (3), and is prepared by spinning or stamping. A through hole is reserved at the top of the bottom of the hemispherical metal liner box (2), and it is connected to the metal liner section (3) by welding or flange connection. The metal liner section (3) has a circumferential variable thickness distribution and / or an axial variable thickness distribution; the thickness is increased in the critical stress area and the wall thickness is reduced in the non-critical area.

2. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 1, characterized in that, In the circumferential and axial variable thickness distributions, the length of the spiral corresponding to each thickness region is determined based on the number of turns and the length of a single spiral turn.

3. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 2, characterized in that, The length of the single-turn spiral d is the diameter of the helix, and p is the pitch.

4. The variable thickness cryogenic storage tank thin-walled metal liner according to any one of claims 1-3, characterized in that, The thickness of the metal inner liner section (3) is increased at the two ends where it connects to the bottom (2) of the hemispherical metal inner liner box, and the thickness of the middle part of the metal inner liner section (3) is reduced.

5. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 4, characterized in that, The variable thickness metal strip is made of aluminum alloy or stainless steel.

6. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 5, characterized in that, The variable thickness metal strip is produced by a continuous casting machine, heat-treated in a heating furnace, then rolled by a rolling mill according to the thickness distribution of the strip, and finally straightened by a straightener and cut and coiled by a flying shear to a coiler to obtain variable thickness strip coils.

7. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 6, characterized in that, The seam of the metal inner tube section (3) is sealed by using sealant.

8. The thin-walled metal liner of the variable thickness cryogenic storage tank according to claim 7, characterized in that, The adhesive is a low-temperature environment sealant.

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