Preparation method and testing method of leakage sample of high-pressure gas cylinder

Abstract

The application provides a preparation method and a test method of a high-pressure cylinder leakage sample. The test method comprises the following steps: providing a leakage sample and a detection device for leakage performance detection; mounting the leakage sample in a groove of a first clamp, wherein a carbon fiber sample and a first cladding layer are accommodated in the groove, and a second cladding layer is embedded in a first channel or a second channel; after connecting all components of the detection device, testing the leakage of the leakage sample according to a preset test process, and obtaining an indication of a helium mass spectrum leak detector. The second cladding layer with a different outer diameter from the first cladding layer is embedded in a helium inlet or a helium outlet to solve the technical problem of inconvenient sealing caused by the thickness difference, and the application has the advantages of convenient testing and high testing accuracy.

Description

Technical Field

[0001] This invention belongs to the field of high-pressure gas cylinder leakage testing technology, specifically relating to a method for preparing and testing a high-pressure gas cylinder leakage sample. Background Technology

[0002] With the rapid development of aerospace technology, spacecraft need to perform heavy and complex space missions. Currently, most spacecraft in aerospace systems, such as artificial satellites, space shuttles, launch vehicles, and space stations, require a large number of pressure vessels to store various liquids or gases to maintain the normal operation of subsystems. Developing high-performance high-pressure gas cylinders is crucial for the long-term on-orbit flight of spacecraft.

[0003] Gas cylinders can be broadly classified into two categories based on their application and structure: metal cylinders and composite material cylinders. Currently, composite material cylinders operating in liquid hydrogen and liquid oxygen environments require solutions to permeability and liquid oxygen compatibility issues. Related technologies employ a composite structure of a metal liner, a composite material layer, and a metal cladding layer to address this problem. Specifically, since high-pressure cylinders consist of a central cylinder body, end caps and heads located at both ends of the cylinder body, and a nozzle connected to the end caps, the metal cladding layer is applied in segments. Overlaps are required at the connections between the cylinder body and the end cap, the cylinder body and the head cap, and the head cap and the nozzle. The presence of these overlaps creates thickness differences on the sample surface, making it difficult to seal leaky samples.

[0004] Patent application CN202111441863.9 uses distributed fiber optic sensors to determine the location of maximum strain in a loaded pure composite pressure vessel and measures the leakage rate at this location. Through linear interpolation, cubic B-spline interpolation, and least squares method, the strain-leakage correlation law of the composite pressure vessel is established. However, this method requires attaching several distributed fiber optic sensors and temperature sensors during the test, then performing strain compensation in areas with large temperature fluctuations, and finally reconstructing the strain of the entire composite gas cylinder. The operation process is relatively complex and the data processing is cumbersome. Even with the above method, it is not possible to effectively determine the leakage performance at the cemented joint. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and testing a leakage sample with an overlapping portion. By embedding a second coating layer with a different outer diameter than the first coating layer into the helium inlet or helium outlet, the technical problem of inconvenient sealing caused by the thickness difference is solved. This method has the advantages of convenient testing and high testing accuracy.

[0006] To achieve the above objectives, the present invention provides a method for preparing a leakage sample of a high-pressure gas cylinder with an overlapping portion. The high-pressure gas cylinder is used in a liquid oxygen or liquid hydrogen environment. The shell wall of the high-pressure gas cylinder has a multi-layer structure, and the outermost metal layer includes a body portion that exactly covers the next outermost metal layer or composite material layer, and a cylinder overlapping portion extending from the body portion. The method for preparing the leakage sample includes the following steps:

[0007] (1) A carbon fiber coating layer is prepared according to a preset molding process, and the carbon fiber coating layer is cut into a circular carbon fiber sample with a preset diameter.

[0008] (2) Provide a first covering layer in a concentric ring shape and a second covering layer for covering the central through hole of the first covering layer, wherein the outer diameter of the first covering layer is the same as the preset diameter of the carbon fiber sample, and the diameter of the second covering layer is greater than the inner diameter of the first covering layer and smaller than the outer diameter of the first covering layer.

[0009] (3) Apply pretreated DW-3 low-temperature adhesive to the upper and lower surfaces of the first coating layer respectively, and connect the first coating layer to the carbon fiber sample and the second coating layer respectively to obtain a leakage sample to be cured. The first coating layer is sandwiched between the carbon fiber sample and the second coating layer, the second coating layer is covered on the central through hole, and the central axis of the carbon fiber sample, the central axis of the first coating layer and the central axis of the second coating layer are all on the same straight line. The part where the first coating layer and the second coating layer are connected is the sample overlap part.

[0010] (4) After sealing the leakage sample to be cured, place it in a thermostatic jar and cure it according to the preset curing process to obtain the leakage sample.

[0011] In one specific embodiment, the preset molding process includes: heating from room temperature to 90°C at a heating rate of 1.5°C / min, holding at that temperature for 1 hour, then heating to 120°C at a heating rate of 1.5°C / min, holding at that temperature for 2 hours, then heating to 150°C at a heating rate of 1.5°C / min, holding at that temperature for 3 hours, and finally cooling naturally.

[0012] In one specific embodiment, the preset curing process includes: heating from room temperature to 40℃-55℃ at a heating rate of 1.5℃ / min, increasing the pressure in the autoclave to 0.05-0.1MPa at a pressure increase rate of 0.02MPa / min, holding at the temperature for 7-9 hours, and drawing a 0.1MPa vacuum in the vacuum bag containing the leaking sample to be cured throughout the entire process.

[0013] In one specific embodiment, the pretreatment of the DW-3 low-temperature adhesive includes a degassing process and a heat treatment process performed sequentially.

[0014] In one specific embodiment, the degassing process is carried out in a vacuum stirring degassing machine. The degassing process includes a fourth stage performed sequentially. In the first stage, the stirring speed is 0 r / min and the vacuum degree inside the degassing machine is 30 kPa. In the second stage, the stirring speed is 500 r / min and the vacuum degree inside the degassing machine is 7-9 kPa. In the third stage, the stirring speed is 1900-2100 r / min and the vacuum degree inside the degassing machine is 3-5 kPa. In the fourth stage, the stirring speed is 450-600 r / min and the vacuum degree inside the degassing machine is 30 kPa.

[0015] In one specific implementation, the time corresponding to the first stage is 0-10s, the time corresponding to the second stage is 11-25s, the time corresponding to the third stage is 26-115s, and the time corresponding to the fourth stage is 116-125s.

[0016] In one specific embodiment, the parameters of the heat treatment process are: heating temperature of 60℃~70℃ and holding time of 50~70min.

[0017] In one specific implementation, step (1) includes the following steps:

[0018] A flat template is provided, and carbon fiber filaments impregnated in a glue tank are wound onto the flat template according to a preset winding process to obtain a carbon fiber coating layer to be cured.

[0019] A molding die for compression molding is provided, the molding die comprising an upper die and a lower die with identical structures, the upper die and the lower die each comprising a die body, a protrusion extending from the die body, and a plurality of screw holes respectively opened on both sides of the die body;

[0020] The carbon fiber coating layer to be cured is sandwiched between the protrusions of the upper mold and the protrusions of the lower mold, and the upper mold and the lower mold are locked together by bolts to obtain a closed molding mold.

[0021] The closed molding die is placed in a heating furnace, and the carbon fiber filaments are cured according to the preset molding process to obtain a carbon fiber coating layer.

[0022] The carbon fiber coating is cut into circular carbon fiber samples with a predetermined diameter.

[0023] The present invention provides a leakage specimen, which is a leakage specimen prepared by the preparation method described above. The leakage specimen includes a first coating layer, a carbon fiber specimen respectively disposed on both sides of the first coating layer and connected to the first coating layer by DW-3 low temperature adhesive, and a second coating layer. The first coating layer has a concentric ring structure, and the second coating layer covers the central through hole of the first coating layer. The central axis of the first coating layer, the central axis of the carbon fiber specimen, and the central axis of the second coating layer are all located on the same straight line.

[0024] The present invention also provides a test method for a leakage sample, comprising the following steps:

[0025] Provide leakage samples and testing equipment for leakage performance testing; wherein,

[0026] The leakage test specimen is the leakage test specimen described above;

[0027] The testing device includes a test fixture, which includes a first fixture and a second fixture disposed opposite to each other. The first fixture includes a first fixture body, a first extension extending from the middle of the first fixture body in a direction away from the second fixture, a groove formed by recessing inward from the surface of the first fixture body toward the second fixture, and a first channel formed by penetrating the bottom of the groove along a first direction through the first extension and the groove. The second fixture includes a second fixture body, a second extension extending from the middle of the second fixture body in a direction away from the first fixture, and a first channel formed by recessing inward from the surface of the second fixture body toward the second fixture. The device includes a protrusion extending toward the first fixture and a second channel forming the second extension and the protrusion along the first direction, wherein the shape of the protrusion matches the shape of the groove; the detection device also includes a cryogenic chamber for housing the test fixture, a liquid nitrogen tank connected to the cryogenic chamber, a helium tank connected to the first channel of the test fixture via a helium pipeline, a vacuum pump connected to the helium pipeline via a first connecting pipe, a pressure gauge installed at one end of the helium pipeline near the helium tank, and a helium mass spectrometer leak detector connected to the second channel of the test fixture via a second connecting pipe;

[0028] The leakage sample is installed in the groove of the first fixture, wherein the carbon fiber sample and the first coating layer are housed in the groove, and the second coating layer is embedded in the first channel or the second channel;

[0029] After connecting all the components of the detection device, the leakage of the leakage sample is tested according to the preset test process, and the reading of the helium mass spectrometer leak detector is obtained.

[0030] The beneficial effects of the present invention include at least the following:

[0031] I. This invention simplifies the evaluation of leakage rate of curved cemented structure specimens to evaluation using flat plate specimens. A specific preparation method is used to prepare the leakage specimen, enabling it to withstand the low temperatures of liquid nitrogen and liquid hydrogen environments. During testing, a second coating layer, including the overlapping portion, is embedded in the first or second channel, while the carbon fiber specimen and the first coating layer are housed within a groove. This solves the problem of difficulty in sealing leakage specimens due to thickness differences on the specimen surface. Using the leakage specimen of this invention in conjunction with its testing method solves the problems existing in the prior art and has the advantages of simple operation, convenient testing, and high testing accuracy.

[0032] II. The method for preparing leakage samples used in this invention involves pre-treating DW-3 low-temperature adhesive to increase its viscosity and facilitate even application. The pre-set curing process ensures that the DW-3 low-temperature adhesive does not delaminate at -196℃, thus not affecting the leakage rate test. Furthermore, it guarantees that the adhesive joints maintain high strength under low-temperature conditions, enabling them to withstand the pressure applied during the test.

[0033] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0034] Figure 1 This is a partial structural diagram of a high-pressure gas cylinder with an overlapping portion provided in an embodiment of the present invention;

[0035] Figure 2 This is a schematic flowchart of the steps for preparing a leakage sample of a high-pressure gas cylinder with an overlapping part according to an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of the structure of a leakage sample provided in an embodiment of the present invention;

[0037] Figure 4 This is a schematic flowchart of the testing method for a leakage sample provided in an embodiment of the present invention.

[0038] Figure 5 This is a connection block diagram of a detection device for leakage performance testing according to an embodiment of the present invention;

[0039] Figure 6 for Figure 5 A schematic diagram of the test fixture of the detection device at one angle.

[0040] Explanation of reference numerals in the attached figures:

[0041] bottle mouth 214 Metal layer 221 Body part 2211 Gas cylinder joint 2212 Leakage test sample 300 First coating layer 310 Center through hole 311 carbon fiber specimens 320 Second coating layer 330 Body part 331 Sample overlap 332 Detection device 100 Test fixture 10 First clamp 11 First clamp main body 111 First Extension 112 groove 113 First Channel 114 Second clamp 12 Second clamp main body 121 Second extension 122 boss 123 Second Channel 124 cryogenic chamber 20 liquid nitrogen tank 30 helium tank 40 vacuum pump 50 pressure gauge 60 Helium mass spectrometer leak detector 70 Helium pipeline 91 First connecting pipe 92 Second connecting pipe 93 Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be limited to and covered by various different embodiments according to the claims.

[0043] With the rapid development of aerospace technology, spacecraft need to perform heavy and complex aerospace missions. Currently, most spacecraft in aerospace systems, such as artificial satellites, space shuttles, launch vehicles, and space stations, require a large number of pressure vessels to store various liquids or gases to maintain the normal operation of subsystems. High-pressure gas cylinders, as containers for storing various liquids and gases, need to be used in liquid oxygen or liquid hydrogen environments. Therefore, after the high-pressure gas cylinders are manufactured, their leakage performance needs to be tested in a cryogenic environment.

[0044] When there is an overlap in the high-pressure gas cylinder, it is difficult to seal the leakage sample due to the thickness difference on the sample surface. Existing technology requires strain reconstruction of the high-pressure gas cylinder and the attachment of several distributed optical fiber sensors and temperature sensors for detection. The data processing is cumbersome and cannot effectively measure the leakage performance at the cemented joint.

[0045] Please see Figure 1 The structure of the high-pressure gas cylinder with overlapping parts is as follows: The high-pressure gas cylinder includes a cylinder body 211 located in the middle, a bottom seal 212 and a top seal 213 located at both ends of the cylinder body 211, and a bottle mouth 214 connected to the top seal 213. The shell wall of the high-pressure gas cylinder has a multi-layer structure, and the outermost metal layer 221 includes a body part 2211 that just covers the next outermost metal layer or composite material layer, and a bottle body overlapping part 2212 extending from the body part 2211. There are multiple bottle body overlapping parts, and the multiple bottle body overlapping parts are respectively arranged at the connection between the cylinder body 211 and the bottom seal 212, and at the connection between the cylinder body 211 and the top seal 213.

[0046] The above description only illustrates one structure of a high-pressure gas cylinder to facilitate understanding of the overlapping portion structure in related technologies. In other embodiments, the overlapping portion can also be located at the connection between the end cap and the cylinder neck, etc., which is not limited in this invention. The limitation of this invention is that the overlapping portion structure of the high-pressure gas cylinder presents a defect that makes sealing inconvenient, thus making the testing of the leakage rate at the joint relatively complex and inconvenient. To solve the above technical problems, this invention provides a test method and a method for preparing leakage samples suitable for testing the leakage rate of the high-pressure gas cylinder described above.

[0047] Please see Figure 2This invention provides a method for preparing a leakage sample of a high-pressure gas cylinder with an overlapping portion. The high-pressure gas cylinder is used in a liquid oxygen or liquid hydrogen environment. The shell wall of the high-pressure gas cylinder has a multi-layer structure, and the outermost metal layer includes a body portion that exactly covers the next outermost metal layer or composite material layer, and a cylinder overlapping portion extending from the body portion. The method for preparing the leakage sample includes the following steps:

[0048] S11. A carbon fiber coating layer is prepared according to a preset molding process, and the carbon fiber coating layer is cut into a circular carbon fiber sample with a preset diameter.

[0049] This step specifically includes:

[0050] Step (1) Provide a flat template, and wind the carbon fiber filaments impregnated in the glue tank onto the flat template according to the preset winding process to obtain the carbon fiber coating layer to be cured;

[0051] In this embodiment, the flat template is rectangular.

[0052] In this embodiment, the carbon fiber filament used is T700SC-12k, and the resin placed in the glue tank is C601G resin.

[0053] Preferably, the preset winding process includes: using an automatic winding device to control the winding angle of the carbon fiber to ±89°, ±12°, ±89°, ±25°, ±89°, ±32°, ±89°, ±42°, ±89°.

[0054] The winding angle is explained in detail as follows: first, the first round of circumferential winding is carried out at ±89°, then the second round of longitudinal winding is carried out at ±12°, and so on, winding is carried out for 9 rounds according to the above angle. After the winding is completed, a total of 18 layers of carbon fiber filaments are wound on the flat template.

[0055] It should be noted that the winding at ±89° is circumferential winding, while the winding at other angles is longitudinal winding. Since circumferential winding can eliminate the circumferential stress generated by the internal pressure of the gas cylinder, while longitudinal winding can provide longitudinal stress, the present invention uses an alternating winding method of circumferential and longitudinal winding, which can improve the overall performance of the carbon fiber coating.

[0056] Step (2) provides a molding die for compression molding, the molding die including an upper die and a lower die with the same structure, the upper die and the lower die each including a die body, a protrusion extending from the die body, and a plurality of screw holes respectively opened on both sides of the die body;

[0057] In this embodiment, the number of screw holes on both sides of the mold body is the same, and they are symmetrically arranged about the central axis of the mold body.

[0058] Step (3) The carbon fiber coating layer to be cured is sandwiched between the protrusion of the upper mold and the protrusion of the lower mold, and the upper mold and the lower mold are locked together by bolts to obtain a closed molding mold;

[0059] Specifically, a bolt is installed in each screw hole to lock the upper and lower molds, making disassembly and installation convenient.

[0060] Step (4) Place the closed molding mold in a heating furnace and cure the carbon fiber filaments according to the preset molding process to obtain a carbon fiber coating layer.

[0061] The preset molding process includes: heating from room temperature to 90°C at a heating rate of 1.5°C / min, holding at that temperature for 1 hour, then heating to 120°C at a heating rate of 1.5°C / min, holding at that temperature for 2 hours, then heating to 150°C at a heating rate of 1.5°C / min, holding at that temperature for 3 hours, and finally cooling naturally with the molding mold.

[0062] Step (5) cut the carbon fiber coating layer into a circular carbon fiber sample with a preset diameter.

[0063] After the molding mold cools down, the carbon fiber coating layer wrapped around the flat template is removed and cut with a cutting machine to cut the carbon fiber coating layer into circular samples with a preset diameter, i.e., circular carbon fiber samples.

[0064] Preferably, the preset diameter is 70mm to 100mm.

[0065] S12. A first covering layer in a concentric ring shape is provided, and a second covering layer for covering the central through hole of the first covering layer. The outer diameter of the first covering layer is the same as the preset diameter of the carbon fiber sample, and the diameter of the second covering layer is greater than the inner diameter of the first covering layer and smaller than the outer diameter of the first covering layer.

[0066] It should be noted that the concentric ring shape can be understood as the central axis of the first coating layer and the central axis of the central through hole of the first coating layer being on the same straight line, that is, the center of the first coating layer and the center of the central through hole coincide (without considering the thickness of the first coating layer).

[0067] In this embodiment, the first coating layer can be processed from a circular coating layer with the same size as the carbon fiber sample. That is, this step can also be to provide a circular coating layer with the same size as the carbon fiber sample and open a central through hole in the middle of the circular coating layer to obtain the first coating layer.

[0068] It is understood that the hollow portion of the first covering layer is a circular through hole, and the inner diameter of the first covering layer is the diameter of the hollow portion of the first covering layer.

[0069] In this embodiment, the outer diameter of the first coating layer is the same as the diameter of the carbon fiber sample. For example, when the diameter of the carbon fiber sample is 80 mm, the outer diameter of the first coating layer is also 80 mm.

[0070] In this embodiment, the inner diameter of the first coating layer is related to the size of the drill bit of the processing equipment and the overlap length, which will be further described below.

[0071] The second covering layer is used to cover the hollow portion of the first covering layer. The diameter of the second covering layer is defined as being larger than the inner diameter of the first covering layer and smaller than the outer diameter of the first covering layer, so that after the carbon fiber sample, the first covering layer and the second covering layer are connected, a sample overlap portion is formed.

[0072] It is understandable that in this step, the size of the first and second covering layers is defined by the diameter, which is equivalent to defining the outer periphery of the first covering layer as circular, the inner periphery of the first covering layer as circular, and the second covering layer as circular.

[0073] S13. Apply pretreated DW-3 low-temperature adhesive to the upper and lower surfaces of the first coating layer, and connect the first coating layer to the carbon fiber sample and the second coating layer respectively to obtain a leakage sample to be cured. The first coating layer is sandwiched between the carbon fiber sample and the second coating layer, and the second coating layer is covered on the central through hole. The central axis of the carbon fiber sample, the central axis of the first coating layer and the central axis of the second coating layer are all on the same straight line. The part where the first coating layer and the second coating layer are connected is the sample overlap.

[0074] The design of the overlap section adopts the layering method. First, a central through hole is opened on the circular covering layer to obtain the first covering layer in the shape of a ring. Then, a second covering layer is covered on the first covering layer. Since the size of the second covering layer is larger than the size of the central through hole but smaller than the size of the first covering layer, the part where the second covering layer and the first covering layer are connected forms the sample overlap section. It can also be understood that the size of the second covering layer that exceeds the central through hole is the sample overlap section.

[0075] In this embodiment, the width of the sample overlap is half the difference between the diameter of the second coating layer and the diameter of the central through hole. Preferably, the width of the sample overlap can be varied, thereby optimizing the width of the high-pressure gas cylinder overlap through multiple experiments. When the size of the sample overlap has an optimal value, the high-pressure gas cylinder is the lightest and has the best leakage resistance. Specifically:

[0076] When the inner diameter of the first coating layer is determined, the size of the second coating layer can be adjusted to obtain leakage samples with different overlap lengths for testing. When the diameter of the second coating layer is determined, the inner diameter of the first coating layer can be adjusted to obtain leakage samples with different overlap lengths for testing.

[0077] Preferably, the pretreatment of the DW-3 low-temperature adhesive includes a degassing process and a heat treatment process performed sequentially. Pretreatment of the DW-3 low-temperature adhesive can increase its viscosity and facilitate application.

[0078] Preferably, the adhesive bonding width is 15–25 mm.

[0079] More preferably, the degassing process is carried out in a vacuum stirring degassing machine, which includes four stages performed sequentially. In the first stage, the stirring speed is 0 r / min and the vacuum degree inside the degassing machine is 30 kPa. In the second stage, the stirring speed is 500 r / min and the vacuum degree inside the degassing machine is 7-9 kPa. In the third stage, the stirring speed is 1900-2100 r / min and the vacuum degree inside the degassing machine is 3-5 kPa. In the fourth stage, the stirring speed is 450-600 r / min and the vacuum degree inside the degassing machine is 30 kPa.

[0080] More preferably, the time corresponding to the first stage is 0-10s, the time corresponding to the second stage is 11-25s, the time corresponding to the third stage is 26-115s, and the time corresponding to the fourth stage is 116-125s.

[0081] More preferably, the parameters of the heat treatment process are: heating temperature 60℃-70℃; holding time 50-70min.

[0082] S14. After sealing the leaking sample to be cured, cure it according to the preset curing process to obtain the leaking sample.

[0083] Methods for sealing leaking samples that are yet to be cured include:

[0084] Use pressure-sensitive adhesive tape to wrap and fix the leakage sample to be cured.

[0085] Provide a flat mold, place the high-temperature sealant around the flat mold, place a release film on the flat mold (to prevent the sealant from overflowing and making demolding difficult), and place the leakage sample to be cured on the surface of the release film.

[0086] Next, place the isolation membrane, breathable felt, and vacuum bag on top of the leakage sample to be cured in sequence. Press the vacuum bag and high-temperature sealant to seal them together. Connect the vacuum nozzle connected to the vacuum bag to the vacuum tube. After sealing, place it in an autoclave.

[0087] The preset curing process includes: when the vacuum pressure of the vacuum bag is reduced to 100 kPa (0.1 MPa), the vacuuming is stopped, and after 10-15 minutes, when the vacuum degree is not lower than 100 kPa, it is placed in an autoclave for heating and pressurization curing. The curing process parameters are: heating from room temperature to 40-55℃ at a rate of 1.5℃ / min, pressurizing at a rate of 0.02 MPa / min to 0.05-0.1 MPa, and holding at the temperature for 7-9 hours.

[0088] It should be noted that the vacuum pressure reaching 100 kPa refers to evacuating the vacuum bag, while the pressure increase rate of 0.02 MPa / min to 0.05-0.1 MPa refers to pressurizing the autoclave. Using the above-described curing process ensures that the DW-3 low-temperature adhesive does not delaminate at -269℃, thus not affecting leakage rate testing in liquid nitrogen and liquid hydrogen environments. Furthermore, it guarantees high strength at the bonded joints under low-temperature conditions, enabling them to withstand the pressure applied during testing.

[0089] It should be noted that the vacuum bag can be placed in an autoclave before vacuuming, and the order of these steps does not affect the implementation of the present invention.

[0090] Please refer to the following: Figure 3 The present invention also provides a leakage sample, which is prepared by the preparation method described above. The leakage sample 300 includes a first coating layer 310, a carbon fiber sample 320 respectively disposed on both sides of the first coating layer 310 and connected to the first coating layer by DW-3 low-temperature adhesive, and a second coating layer 330. The first coating layer 310 has a concentric ring structure, and the second coating layer 330 covers the central through hole 311 of the first coating layer 310. The central axis of the first coating layer 310, the central axis of the carbon fiber sample 320, and the central axis of the second coating layer 330 are all located on the same straight line.

[0091] In this embodiment, the second covering layer 330 includes a body portion 331 covering the central through hole 311 and an overlapping portion 332 connected to the first covering layer 310.

[0092] Please refer to the following: Figures 3 to 6 The present invention also provides a test method for a leakage sample, comprising the following steps:

[0093] Step S21: Provide a leakage sample and a testing device for leakage performance testing;

[0094] The structure of the leakage sample is as described above, namely: the leakage sample 300 includes a first covering layer 310, a carbon fiber sample 320 respectively disposed on both sides of the first covering layer 310 and connected to the first covering layer by DW-3 low temperature adhesive, and a second covering layer 330. The first covering layer 310 has a concentric ring structure, and the second covering layer 330 covers the central through hole 311 of the first covering layer 310. The central axis of the first covering layer 310, the central axis of the carbon fiber sample 320, and the central axis of the second covering layer 330 are all located on the same straight line.

[0095] The leakage sample was prepared using the method described above. The DW-3 low-temperature adhesive can withstand a low temperature of -269℃, so the DW-3 low-temperature adhesive layer will not affect the test results of leakage performance.

[0096] The testing device 100 includes a test fixture 10, which includes a first fixture 11 and a second fixture 12 disposed opposite to each other. The first fixture 11 includes a first fixture body 111, a first extension 112 extending from the middle of the first fixture body 111 in a direction away from the second fixture 12, a groove 113 formed inwardly from the surface of the first fixture body 111 toward the second fixture 12, and a first channel 114 formed through the bottom of the groove along a first direction, penetrating the first extension 112 and the groove 113. The second fixture 12 includes a second fixture body 121, a second extension 122 extending from the middle of the second fixture body 121 in a direction away from the first fixture 11, and a first channel 114 extending from the surface of the second fixture body 121 toward the first fixture 12. The device includes a protrusion 123 extending in the first direction and a second channel 124 forming the second extension 122 and the protrusion 123, the shape of which matches the shape of the groove 113; the detection device 100 also includes a cryogenic chamber 20 for housing the test fixture 10, a liquid nitrogen tank 30 communicating with the cryogenic chamber 10, a helium tank 40 communicating with the first channel 114 of the test fixture 10 via a helium pipe 91, a vacuum pump 50 communicating with the helium pipe 91 via a first connecting pipe 92, a pressure gauge 60 installed on the helium pipe 91 near the end of the helium tank, and a helium mass spectrometer leak detector 70 communicating with the second channel 124 of the test fixture 10 via a second connecting pipe 93; the test fixture 10 is housed in the cryogenic chamber 20.

[0097] In this embodiment, the first direction is the extension direction of the first channel and the second channel.

[0098] In this embodiment, the first channel 114 is a helium inlet, and the second channel 124 is a helium outlet.

[0099] In this embodiment, the pressure gauge 60 is used to detect the pressure between the outlet end of the helium tank and the helium inlet end of the first clamp, so as to facilitate control of the pressure of the detected helium.

[0100] Step S22: Install the leakage sample into the groove of the first fixture, wherein the carbon fiber sample and the first coating layer are housed in the groove, and the second coating layer is embedded in the first channel or the second channel;

[0101] Step S23: After connecting all the components of the detection device, test the leakage of the leakage sample according to the preset test process, and obtain the reading of the helium mass spectrometer leak detector.

[0102] The testing process includes: first, turning on the vacuum pump to extract helium from the helium pipeline; when the pressure gauge reads -0.1 MPa, turning off the vacuum pump and closing the outlet valve of the sample fixture; turning on the gas supply switch of the helium tank; and turning off the gas supply switch of the helium tank when the pressure gauge reading reaches 4-5 bar. After the pressure gauge reading stabilizes, turning on the outlet switch of the liquid nitrogen tank to start cooling the cryogenic chamber. Maintaining the cryogenic chamber at a temperature of -196 to -180°C, high-pressure helium is passed through the leaking sample to be tested, and the reading of the helium mass spectrometer leak detector is obtained. This reading is the leakage rate of the leaking sample to be tested.

[0103] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions and substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a leakage sample of a high-pressure gas cylinder with an overlapping portion, wherein the high-pressure gas cylinder is used in a liquid oxygen environment or a liquid hydrogen environment, the shell wall of the high-pressure gas cylinder has a multi-layer structure, and the outermost metal layer includes a body portion that exactly covers the next outermost metal layer or composite material layer, and a cylinder overlapping portion extending from the body portion, the method for preparing the leakage sample includes the following steps: (1) A carbon fiber coating layer is prepared according to a preset molding process, and the carbon fiber coating layer is cut into a circular carbon fiber sample with a preset diameter. (2) Provide a first coating layer in a concentric ring shape and a second coating layer for covering the central through hole of the first coating layer, wherein the outer diameter of the first coating layer is the same as the preset diameter of the carbon fiber sample, and the diameter of the second coating layer is greater than the inner diameter of the first coating layer and smaller than the outer diameter of the first coating layer. (3) Apply pretreated DW-3 low-temperature adhesive to the upper and lower surfaces of the first coating layer respectively, and connect the first coating layer to the carbon fiber sample and the second coating layer respectively to obtain a leakage sample to be cured. The first coating layer is sandwiched between the carbon fiber sample and the second coating layer, and the second coating layer is covered on the central through hole. The central axis of the carbon fiber sample, the central axis of the first coating layer and the central axis of the second coating layer are all on the same straight line. The part where the first coating layer and the second coating layer are connected is the sample overlap part. (4) After sealing the leakage sample to be cured, place it in a thermostatic jar and cure it according to the preset curing process to obtain the leakage sample.

2. The preparation method according to claim 1, characterized in that, The preset molding process includes: heating from room temperature to 90°C at a heating rate of 1.5°C / min, holding at that temperature for 1 hour, then heating to 120°C at a heating rate of 1.5°C / min, holding at that temperature for 2 hours, then heating to 150°C at a heating rate of 1.5°C / min, holding at that temperature for 3 hours, and finally cooling naturally.

3. The preparation method according to claim 1, characterized in that, The preset curing process includes: heating from room temperature to 40℃-55℃ at a heating rate of 1.5℃ / min, increasing the pressure in the autoclave to 0.05-0.1MPa at a pressure rate of 0.02MPa / min, holding at the temperature for 7-9 hours, and drawing a 0.1MPa vacuum in the vacuum bag containing the leaking sample to be cured throughout the entire process.

4. The preparation method according to claim 1, characterized in that, The pretreatment of the DW-3 low-temperature adhesive includes a degassing process and a heat treatment process performed sequentially.

5. The preparation method according to claim 4, characterized in that, The degassing process is carried out in a vacuum stirring degassing machine, which includes four stages performed sequentially. In the first stage, the stirring speed is 0 r / min and the vacuum degree inside the degassing machine is 30 kPa. In the second stage, the stirring speed is 500 r / min and the vacuum degree inside the degassing machine is 7-9 kPa. In the third stage, the stirring speed is 1900-2100 r / min and the vacuum degree inside the degassing machine is 3-5 kPa. In the fourth stage, the stirring speed is 450-600 r / min and the vacuum degree inside the degassing machine is 30 kPa.

6. The preparation method according to claim 5, characterized in that, The first stage corresponds to the time from 0 to 10 seconds, the second stage corresponds to the time from 11 to 25 seconds, the third stage corresponds to the time from 26 to 115 seconds, and the fourth stage corresponds to the time from 116 to 125 seconds.

7. The preparation method according to any one of claims 4 to 6, characterized in that, The parameters of the heat treatment process are: heating temperature of 60℃~70℃; holding time of 50~70 min.

8. The preparation method according to claim 1, characterized in that, Step (1) includes the following steps: A flat template is provided, and carbon fiber filaments impregnated in a glue tank are wound onto the flat template according to a preset winding process to obtain a carbon fiber coating layer to be cured. A molding die for compression molding is provided, the molding die comprising an upper die and a lower die with identical structures, the upper die and the lower die each comprising a die body, a protrusion extending from the die body, and a plurality of screw holes respectively opened on both sides of the die body; The carbon fiber coating layer to be cured is sandwiched between the protrusions of the upper mold and the protrusions of the lower mold, and the upper mold and the lower mold are locked together by bolts to obtain a closed molding mold. The closed molding die is placed in a heating furnace, and the carbon fiber filaments are cured according to the preset molding process to obtain a carbon fiber coating layer. The carbon fiber coating is cut into circular carbon fiber samples with a predetermined diameter.

9. A leakage test sample, characterized in that, The leakage sample is a leakage sample prepared by the preparation method according to any one of claims 1 to 8. The leakage sample includes a first coating layer, a carbon fiber sample respectively disposed on both sides of the first coating layer and connected to the first coating layer by DW-3 low temperature adhesive, and a second coating layer. The first coating layer has a concentric ring structure, and the second coating layer covers the central through hole of the first coating layer. The central axis of the first coating layer, the central axis of the carbon fiber sample, and the central axis of the second coating layer are all located on the same straight line.

10. A method for testing a leakage sample, characterized in that, Includes the following steps: Provide leakage samples and testing equipment for leakage performance testing; wherein, The leakage test specimen is the leakage test specimen according to claim 9; The testing device includes a test fixture, which includes a first fixture and a second fixture disposed opposite to each other. The first fixture includes a first fixture body, a first extension extending from the middle of the first fixture body in a direction away from the second fixture, a groove formed by recessing inward from the surface of the first fixture body toward the second fixture, and a first channel formed by penetrating the bottom of the groove along a first direction through the first extension and the groove. The second fixture includes a second fixture body, a second extension extending from the middle of the second fixture body in a direction away from the first fixture, and a first channel formed by recessing inward from the surface of the second fixture body toward the second fixture. The device includes a protrusion extending toward the first fixture and a second channel forming the second extension and the protrusion along the first direction, wherein the shape of the protrusion matches the shape of the groove; the detection device also includes a cryogenic chamber for housing the test fixture, a liquid nitrogen tank connected to the cryogenic chamber, a helium tank connected to the first channel of the test fixture via a helium pipeline, a vacuum pump connected to the helium pipeline via a first connecting pipe, a pressure gauge installed at one end of the helium pipeline near the helium tank, and a helium mass spectrometer leak detector connected to the second channel of the test fixture via a second connecting pipe; The leakage sample is installed in the groove of the first fixture, wherein the carbon fiber sample and the first coating layer are housed in the groove, and the second coating layer is embedded in the first channel or the second channel; After connecting all the components of the detection device, the leakage of the leakage sample is tested according to the preset test process, and the reading of the helium mass spectrometer leak detector is obtained.

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