A method for overlapping and sealing a high-rigidity carbon fiber composite water tank

Abstract

The present invention relates to a method for overlapping and sealing a high-rigidity carbon fiber composite water tank. The method is based on the high-rigidity structure of a composite water tank. The tank body is divided into two parts, an upper tank body and a lower tank body, which are prepared by a thermal expansion mold forming process and a composite stiffener is installed inside. The core of the present invention is to adopt the upper / lower tank body overlapping assembly reliability sealing guarantee technology, which can not only achieve long-term sealed storage without leakage under full load, but also meet the water pressure resistance stiffness requirements of the tank body. The steps of the method include: step one: upper / lower tank body skin laying; step two: composite stiffener forming; step three: upper / lower tank body forming; step four: composite stiffener drilling; step five: upper / lower tank body overlapping assembly; step six: appearance finishing; step seven: airtightness detection; as shown in Figure 1. The present invention can take into account the high-rigidity structure of the composite tank body while achieving sealing performance, and is suitable for the promotion and application of similar large-scale composite tank sealing assembly forming.

Description

Technical Field

[0001] The present invention relates to the field of carbon fiber composite material box structure design, and in particular to a carbon fiber composite material box sealing assembly molding method. Background Art

[0002] In recent years, the VARI process has been widely used to split composite material boxes, with the upper / lower box joint area being designed with a flange and fixed by screwing (welding) + gluing.

[0003] Patent publication CN 113510944A, a prior art publication, proposes a lightweight composite fuel tank for missiles and its manufacturing method. The upper and lower covers of the composite fuel tank are formed separately using an expansion film molding method and then assembled using sealant adhesive. To ensure structural strength and rigidity, an anti-sway plate is installed inside the tank.

[0004] Patent document CN 105501685A in the prior art proposes an ultra-large composite pressurized packaging box. Its structural design uses a sandwich core material vacuum-molded integrally, with inner and outer skins covered with glass fiber composite mats, and vacuum resin infusion molding.

[0005] In the prior art, patent document CN 115816859A proposes a low-leakage rate molding method for a glass fiber reinforced resin-based composite material sealed box. The method uses vacuum bag pressing and sealing spraying processes to perform secondary molding on the inner cavity of the box blank, which can effectively improve the airtightness of the composite material packaging box.

[0006] The aforementioned patent (CN 113510944A) focuses on the composite fuel tank molding process and fuel line installation. It provides only a brief description of improving tank rigidity and the method for connecting the upper and lower covers, namely: (1) After the inner skin of the fuel tank is laid, the anti-sway plate is laid in sequence within the mold; and (2) adhesive is evenly applied to the overlapping area of ​​the composite fuel tank upper cover and the composite fuel tank lower cover. It does not cover the structural design and fixing method of the anti-sway plate, the external structure of the upper and lower cover overlapping area, or the composite layup design.

[0007] The aforementioned patent (CN 105501685A) focuses on the design of a packaging box skin layer structure, using a compression molding process to achieve an integrated box body. This has no similarities to the present invention's design of a split box body to achieve a high-rigidity sealed box structure.

[0008] The aforementioned patent (CN 115816859A) improves the sealing performance of composite packaging boxes, optimizing the molding process and proposing a vacuum bagging and sealing spraying process. This patent, which improves the rigidity of the composite box and the sealing performance of the split-structure assembly through structural design, has no similarities to the present invention. Summary of the Invention

[0009] This invention designs a high-rigidity, high-sealing carbon fiber composite water tank structure. Based on a split-type tank assembly method with staggered overlaps and adhesive sealing, the upper and lower tanks are each constructed in a trapezoidal shape to ensure a tight overlap. The tanks are then molded and sealed during assembly. The proven performance is reliable and suitable for the manufacture of sealed composite tanks for similar products.

[0010] The present invention proposes a high-rigidity carbon fiber composite water tank overlap sealing molding method, which is specifically divided into seven steps, wherein step one is the upper / lower tank overlap area shape structure and carbon fiber composite layer design, and step five is the upper / lower tank overlap assembly process. The seven steps include:

[0011] Carry out skin laying of upper and lower box bodies;

[0012] Forming the composite ribs of the upper and lower boxes;

[0013] The upper and lower boxes are formed by using their skin layers and composite stiffeners;

[0014] Drill holes on the composite stiffener to form diversion ports;

[0015] Lap and assemble the formed upper and lower boxes;

[0016] Refine the appearance of the assembled upper and lower boxes;

[0017] Perform airtightness test on the assembled upper and lower boxes.

[0018] The seven steps above are described in detail as follows:

[0019] Step 1: Upper / lower box skin laying

[0020] Preferably, the order of ply laying is: carbon fiber / medium temperature epoxy plain fabric prepreg layer + carbon fiber / medium temperature epoxy unidirectional prepreg layer + adhesive layer + foam sandwich layer + adhesive layer + carbon fiber / medium temperature epoxy unidirectional prepreg layer + carbon fiber / medium temperature epoxy plain fabric prepreg layer, with the foam sandwich layer as the center, and a mirror-symmetrical hierarchical structure design is adopted. The draping is carried out on the female module of the upper / lower box forming mold, and the mold edge reliably fixes the unidirectional prepreg to prevent mutual sliding and dislocation. Among them, the unidirectional prepreg is laid according to the quasi-isotropic rule. The unidirectional prepreg ply does not adopt overlap, and only docking is allowed along the fiber direction, that is, the docking gap is parallel to the fiber direction, and the docking gap width is ≤2mm. Bridging is not allowed in the thickness change area formed by the increase or decrease of the ply and the ply crossing the fillet or step. The overlap area of ​​the upper and lower boxes features a sunken, staggered overlap design. This means a certain width of overlap area is reserved around the edges of the upper and lower boxes. The thickness of the foam core layer laid here equals (the thickness of the foam core layer in the non-overlapping area - the sum of the thickness of the inner and outer carbon fiber unidirectional prepreg skins) / 2. The depth of the sunken overlap area equals the thickness of the foam core layer in the non-overlapping area - the thickness of the foam core layer in the overlapping area. The overlap area width should be between 60mm and 80mm.

[0021] Preferably, after the carbon fiber / medium-temperature epoxy unidirectional prepreg layers are laid, vacuum pre-compaction is performed. The laid-up product is then vacuum-encapsulated. Auxiliary materials, such as a non-porous membrane, breathable felt, and vacuum bags, are then placed on the prepreg surface. Vacuum the prepreg and perform pre-compaction in an oven for 30±5 minutes at 50±5°C, ensuring the vacuum level is consistently no less than -0.09MPa.

[0022] Preferably, the adhesive layer uses J-47A film + J-47B glue (J-47B film is mixed at a concentration of 25-30% by weight, that is, 233-300g of ethyl acetate is added to every 100g of film, and it is soaked for 24 hours and then stirred evenly before use. The prepared J-47B glue should be stored in a sealed state. Before use, it should be taken out of the cold storage or freezer in the original sealed packaging, and placed at room temperature for more than half an hour before unsealing and use. After use, it needs to be resealed and stored in the cold storage or freezer.) Implementation standard Q / HSY 003-2003; manufacturer: Petrochemical Research Institute of Heilongjiang Academy of Sciences. Usage: First lay a layer of J-47A film on the surface of the foam, then apply an appropriate amount of the mixed J-47B glue, and then lay the foam. Among them, the role of the J-47B glue is to improve the viscosity of the adhesive layer to avoid delamination of the product between the prepreg skin and the foam layer after curing.

[0023] Step 2: Composite rib forming

[0024] To meet the high rigidity requirements of the water tank, several composite stiffeners are required inside the tank. Preferably, the composite stiffener structure for the upper and lower tanks is designed as follows: a carbon fiber / medium-temperature epoxy unidirectional prepreg layer + an adhesive layer + a foam core layer + an adhesive layer + a carbon fiber / medium-temperature epoxy unidirectional prepreg layer.

[0025] Raw material cutting: 1) Foam cutting is carried out according to the envelope size of the upper / lower fuel tank cavity; 2) Unidirectional prepreg is laid out in four layers of [0 / +45 / 90 / -45] according to the quasi-isotropic rule, and the four layers of carbon fiber unidirectional prepreg are cut according to the cutting sample design drawing.

[0026] Composite stiffener molding for the upper / lower box: Preferably, an adhesive layer (J-47A adhesive film + J-47B adhesive) is evenly applied to both sides of the foam. Prepreg layers are then laid over both sides of the foam, vacuum-bagging is performed, and the composite stiffener preform is cured in an oven to form the composite stiffener preform.

[0027] Step 3: Upper / lower box forming

[0028] Preferably, the upper / lower tanks are formed using a thermal expansion mold process. After the composite material is draped, the upper / lower tanks are formed separately. The male module consists of a metal core block and a rubber block. During the heating process, the male module expands, compressing the ribs while applying downward pressure to the inner skin of the tank to ensure the internal quality of each part. Specific molding method:

[0029] (1) Fix the composite stiffeners, rubber blocks and metal core blocks. Place the metal core blocks in the mold from front to back; wrap each composite stiffener with a layer of carbon fiber / medium temperature epoxy plain weave prepreg on the front and back, and leave a 30-40mm width of excess material on the edges, folding it into a right angle to form a flange. While placing the core blocks, lay the composite stiffeners and rubber blocks in sequence, so that the flange of the composite stiffeners is close to the inner surface of the box. A jack can be used to assist in the installation process.

[0030] (2) Mold closing. Snap the mold cover onto the mold, tighten the pressure bolts, and finally use the mold closing depth detection pin to check whether the mold is in place.

[0031] (3) Oven curing. Place the mold in the oven and start heating it up. Set the oven temperature at 100±5℃ and heat the mold to 70±5℃. Take the mold out of the oven. Tighten the mold pressure screws again. Check that the mold gap is ≤0.5mm. After passing the test, place the mold in the oven and set the temperature at 170±5℃. When the mold temperature reaches 130±5℃, keep it warm for about 180 minutes. After the holding time is over, the mold begins to cool down with the oven. When the oven temperature drops to 60℃, take the mold out of the oven and prepare for demoulding.

[0032] (4) Demolding. After the product has cured, unscrew the mold pressure bolts, remove the mold cover, take out the core block from the mold, clean the residual resin on the surface, and place it properly. Finally, remove the molding die and remove the product from the mold.

[0033] (5) Finishing. Use fine sandpaper to polish off the small amount of burrs, edges, steps, and wrinkles remaining on the inner and outer surfaces of the product, and ensure a smooth transition between the local areas of the inner surface of the upper box body. Pay attention to the joint between the upper and lower boxes, and the raised part of the fuel tank cover must be polished off to ensure smooth closing of the upper and lower tank covers.

[0034] Step 4: Drilling holes in composite stiffeners

[0035] Drill several holes (preferably 20-30mm in diameter) evenly throughout the composite stiffener to create diversion ports to ensure the tank's stability during full transport. Holes should be drilled in the composite stiffener at the highest and lowest points of the tank to ensure full lateral filling and unloading capacity.

[0036] Step 5: Upper / lower box assembly

[0037] Process the water inlet and outlet ports on the upper and lower housing surfaces. The dimensions and locations should comply with the requirements of the relevant design drawings. Preferably, use J-133C structural adhesive for bonding. The material complies with standard Q / HSY 079-97 and is manufactured by the Institute of Petrochemicals, Heilongjiang Academy of Sciences. Mix the J133C adhesive in a ratio of 2:1 (Component A: Component B). Sand the overlap area of ​​the upper and lower housings to a rough surface. Use a scraper to evenly apply the prepared J-133C adhesive to the overlap area. Place the lower housing on the fixture platform, then firmly snap the upper housing onto the lower housing, ensuring a tight fit. Ensure that the adhesive can clearly flow out of the gap between the upper and lower housings before pressurizing and curing. Allow the product to cure at room temperature for 24-48 hours (or heat at 65±5°C for 3-4 hours). Ensure that any excess adhesive has hardened before removing it from the fixture.

[0038] Step 6: Appearance finishing

[0039] Polish the cured adhesive on the outer surface of the box to ensure a smooth surface and good appearance. Preferably, use fine sandpaper for polishing.

[0040] Step 7: Airtightness test

[0041] According to the relevant product index requirements, the assembled water tank is tested for air tightness to verify the product's sealing performance. Preferably, the water tank's water inlet is connected to the inflation interface, and the water outlet is connected to the deflation interface, with switch valves installed at the interfaces; an air source device is installed at the inflation interface to inflate the tank; a pressure gauge is installed at the deflation interface to detect the real-time pressure value inside the tank. Open the air inlet valve, close the air outlet valve, and fill the water tank with compressed air (or helium with a concentration greater than 95%). While inflating, observe the pressure gauge reading. When the reading reaches the index test requirements, close the air inlet valve and disconnect the air source. Let it stand for 10 to 20 minutes. After the air pressure inside the tank stabilizes, record the pressure gauge reading as the initial pressure value; maintain the pressure for the required time, and record the pressure gauge reading after completion as the final pressure value; also record the ambient temperature values ​​at the initial and final times, and convert the pressure leakage according to the Bernoulli equation.

[0042] If the product meets the airtightness performance index requirements, the water tank has passed the airtightness test. If the product does not meet the airtightness performance index requirements, the water tank is leaking. Preferably, use a leak detector (or helium mass spectrometer) to locate the leak source and repair the leak.

[0043] The present invention also provides a high-rigidity carbon fiber composite water tank formed by the method.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The composite material box of the present invention adopts a split design with several built-in composite stiffeners. The upper / lower box assembly is fixed by bonding through the overlapping area structure, and the outer surface of the box is subjected to a secondary overall layering + curing molding of carbon fiber prepreg to achieve high rigidity and high sealing effects for the box, which can be expanded to the manufacture of large composite material boxes.

[0046] The present invention's structural design and layering process, based on the overlapping locations of the composite box, achieves both higher interface strength and long-term leak-proof reliability. This design balances the high rigidity of the composite box structure with excellent sealing performance, making it suitable for promotion and application in the sealing assembly and molding of similar large composite boxes. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a process flow chart of a composite water tank molding process provided by an example of the present invention.

[0048] Figure 2 This is a schematic diagram of the external structure of a composite material water tank provided by an example of the present invention.

[0049] Figure 3 This is a schematic diagram of the upper / lower box overlap position provided by an example of the present invention.

[0050] Figure 4 It is a schematic cross-sectional view of a composite water tank provided by an example of the present invention.

[0051] Figure 5 It is a schematic diagram of the composite stiffener structure provided by an example of the present invention.

[0052] Figure 6 It is a schematic diagram of the ply structure of the upper / lower box overlap area provided by an example of the present invention.

[0053] In the figure: 1-upper box body; 2-water inlet; 3-water outlet; 4-lower box body; 5-composite ribs; 51-upper box body ribs; 52-flow guide port; 53-lower box body ribs; 54-waste flanging area; 6-carbon fiber / medium temperature epoxy plain weave fabric prepreg (outer skin); 7, 12-carbon fiber / medium temperature epoxy unidirectional prepreg (outer skin); 8, 13-sandwich material in overlapping area; 10, 16-sandwich material in non-overlapping area; 15-carbon fiber / medium temperature epoxy plain weave fabric prepreg (inner skin); 9, 14-carbon fiber / medium temperature epoxy unidirectional prepreg (inner skin); 11-adhesive layer; A-overlapping area. DETAILED DESCRIPTION

[0054] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] One embodiment of the present invention provides a method for overlapping and sealing a carbon fiber / medium temperature epoxy composite water tank. The molding process adopted by the method is as follows: Figure 1 As shown, the structural design and assembly process of the box overlap area are as follows Figure 3 、 Figure 6 shown.

[0056] The water tank overlap sealing molding method of this embodiment includes the following steps:

[0057] Step 1: Upper / lower box skin laying

[0058] The appearance structure of the upper / lower box is as follows Figure 2As shown, it includes an upper box body 1, a water inlet 2, a water outlet 3, and a lower box body 4. Preferably, the ply design of the upper / lower box bodies is: one layer of T300 carbon fiber / medium temperature epoxy plain fabric prepreg layer + 2mm thick T700 carbon fiber / medium temperature epoxy unidirectional prepreg layer + medium temperature epoxy film + 6mm thick PMI foam sandwich layer + medium temperature epoxy film + 2mm thick T700 carbon fiber / medium temperature epoxy unidirectional prepreg layer + T300 carbon fiber / medium temperature epoxy plain fabric prepreg layer.

[0059] The upper box and the lower box have the following features: Figure 3 、 Figure 6 The thickness of the sandwich material 8 used in the overlapping area A is 1 mm, that is, Figure 6 The thickness of the middle sandwich material 8 = [the thickness of the non-overlapping core material 10 - (the thickness of the carbon fiber / medium-temperature epoxy unidirectional prepreg 7 + the thickness of the carbon fiber / medium-temperature epoxy unidirectional prepreg 9)] / 2 = [6-(2+2)] / 2 = 1 mm. Lamination is carried out on the female modules of the upper / lower box forming molds. The mold edges securely secure the unidirectional prepreg to prevent sliding and misalignment. The unidirectional prepreg is laid according to quasi-isotropic principles, and the ply layup order for the 2 mm skin is [0 / +45 / 90 / -45]. 2S Unidirectional prepreg plies are not overlapped and only butt-jointed along the fiber direction is allowed, i.e. the butt joint gap is parallel to the fiber direction and the butt joint gap width is ≤2mm. No bridging is allowed in the thickness variation area formed by the increase or decrease of the plies and where the plies cross the fillet or step. The shape of the upper / lower box overlap area is as follows Figure 6 The sunken, offset overlap design shown here reserves a certain width of overlap area around the edges of the upper and lower boxes. The overlap area's sunken depth is 5mm (i.e., overlap area sunken depth = non-overlapping foam core thickness - overlapping foam core thickness = 6-1 = 5mm). The overlap area width should be between 60 and 62mm.

[0060] After the T700 carbon fiber / medium-temperature epoxy unidirectional prepreg layers are laid, they must be vacuum-pressed and pre-compacted. The laid-up product is then vacuum-encapsulated. Auxiliary materials, such as non-porous membrane, breathable felt, and vacuum bags, are then placed on the prepreg surface. Vacuuming is then performed and pre-compacted in an oven for 30±5 minutes at 50±5°C, ensuring the vacuum level is consistently no less than -0.09MPa.

[0061] The adhesive layer uses J-47A film + J-47B glue (J-47B film is mixed at a concentration of 25-30% by weight, that is, 250g of ethyl acetate is added to every 100g of film, and it is soaked for 24 hours and then stirred evenly before use.) First, lay a layer of J-47A film on the foam surface, then apply an appropriate amount of the mixed J-47B glue, and then lay the foam.

[0062] Step 2: Composite rib forming

[0063] Composite stiffener 5 Figure 4 、 Figure 5 As shown, it includes an upper box rib 51 and a lower box rib 53, each with a guide port 52 and a residual material flange area 54. The composite rib structure is designed as follows: a 1mm thick T700 carbon fiber / medium-temperature epoxy unidirectional prepreg composite layer + a medium-temperature epoxy film + a 3mm thick PMI foam sandwich layer + a medium-temperature epoxy film + a 1mm thick T700 carbon fiber / medium-temperature epoxy unidirectional prepreg composite layer.

[0064] Raw material cutting: 1) Foam cutting is carried out according to the envelope size of the upper / lower fuel tank cavity; 2) Unidirectional prepreg is laid out in four layers [0 / +45 / 90 / -45] according to the quasi-isotropic rule. The thickness of one layer of unidirectional prepreg is 0.125mm. A combination of materials is laid out in four layers, that is, the thickness of one combination of materials is 0.5mm. The four layers of carbon fiber unidirectional prepreg are cut according to the cutting template design drawing.

[0065] Composite stiffener molding: Preferably, evenly apply adhesive layer on both sides of the foam (the adhesive layer uses J-47A adhesive film + J-47B adhesive liquid). Lay the prepreg layer group on both sides of the foam, put in vacuum bag, evacuate to -0.09MPa, and use oven to cure at 130℃ for 2h to form composite stiffener preform. Then install several composite stiffeners at appropriate positions in the upper / lower tank cavity, where the flanges fit the inner skin surface of the tank cavity and are positioned and fixed by metal core blocks. Figure 4 As shown, serial number 5 is a composite stiffener.

[0066] Step 3: Upper / lower box forming

[0067] The upper and lower tanks are formed using a thermal expansion mold process. After the composite material is laid, the upper and lower tanks are formed separately. The male module consists of a metal core block and a rubber block. During the heating process, the male module expands, compressing the ribs while applying downward pressure to the inner skin of the tank to ensure the internal quality of each part. Specific molding method:

[0068] (1) Fix the composite stiffeners, rubber blocks and metal core blocks. Place the metal core blocks in the mold from front to back; wrap each composite stiffener with a layer of T300 carbon fiber / medium temperature epoxy plain weave prepreg on the front and back, and leave a 30mm width of excess material on the edges, folding it into a right angle to form a flange. While placing the core blocks, lay the composite stiffeners and rubber blocks in sequence, so that the flanges of the composite stiffeners are firmly attached to the inner surface of the box. A jack can be used to assist in the installation during the operation.

[0069] (2) Mold closing. Snap the mold cover onto the mold, tighten the pressure bolts, and finally use the mold closing depth detection pin to check whether the mold is in place.

[0070] (3) Oven curing. Place the mold in the oven and start heating it. The oven temperature is set at 100±5℃, and the mold temperature is raised to 70±5℃. Take the mold out of the oven. Tighten the mold pressure screws again. Check that the mold gap is ≤0.5mm. After passing the test, place the mold in the oven and set the temperature at 170±5℃. When the mold temperature reaches 130±5℃, keep it warm for about 180 minutes. After the holding time is over, the mold begins to cool down with the oven. After the oven temperature drops to 60℃, take the mold out of the oven and prepare for demoulding.

[0071] (4) Demolding. After the product has cured, unscrew the mold pressure bolts, remove the mold cover, take out the core block from the mold, clean the residual resin on the surface, and place it properly. Finally, remove the molding die and remove the product from the mold.

[0072] (5) Trim.

[0073] Use 120-grit sandpaper to grind off the small amount of local burrs, edges, steps, and wrinkles remaining on the inner and outer surfaces of the product, and ensure a smooth transition between the local areas of the inner surface of the upper cover; pay attention to the overlapping junction of the upper cover and the lower cover, and the raised part of the overlapping joint of the fuel tank cover must be grinded off to ensure smooth closing of the upper and lower covers of the fuel tank.

[0074] Step 4: Drilling holes in composite stiffeners.

[0075] Drill several Φ20 through holes evenly on the composite stiffener. Figure 5 The diversion port 52 in the tank can maintain the stability of the water tank during full transportation. The composite stiffeners at the highest and lowest points of the water tank need to be machined with through holes to ensure that the water tank can be filled and discharged horizontally.

[0076] Step 5: Overlap and assemble the upper and lower boxes.

[0077] Process the water inlet and outlet on the surface of the upper / lower box, and the size and position should comply with the requirements of the relevant design drawings. Use J-133C structural adhesive for bonding (Component A: Component B = 2:1). Grind the overlapping area of ​​the upper / lower box to a rough surface, and use a scraper to evenly apply the prepared J-133C adhesive to the overlapping area of ​​the upper / lower box. Place the lower box on the fixture platform, and then buckle the upper box onto the lower box steadily, ensuring that the upper / lower box is tightly fitted, so that the adhesive can obviously flow out from the bonding gap of the upper / lower box before it is pressurized and cured. Figure 3 、 4 , 6. After the product is cured at room temperature for 24 hours, check that the overflowed glue has hardened before removing it from the fixture.

[0078] Step 6: Appearance finishing

[0079] Polish the cured glue on the outer surface of the box to ensure a smooth surface and good appearance. Preferably, use 120-grit fine sandpaper for polishing.

[0080] Step 7: Airtightness test

[0081] According to the relevant product index requirements, the assembled water tank is tested for air tightness to verify the product's sealing performance. Preferably, the water tank's water inlet is connected to the inflation interface, and the water outlet is connected to the deflation interface, with switch valves installed at the interfaces; an air source device is installed at the inflation interface to inflate the tank; a pressure gauge is installed at the deflation interface to detect the real-time pressure value inside the tank. Open the air inlet valve, close the air outlet valve, and fill the water tank with compressed air (or helium with a concentration greater than 95%). While inflating, observe the pressure gauge reading. When the reading reaches the index test requirements, close the air inlet valve and disconnect the air source. Let it stand for 10 minutes. After the air pressure inside the tank stabilizes, record the pressure gauge reading as the initial pressure value; maintain the pressure for the required time, and record the pressure gauge reading after completion as the final pressure value; also record the ambient temperature values ​​at the initial and final times, and convert the pressure leakage according to the Bernoulli equation.

[0082] If the product meets the airtightness performance index requirements, the water tank has passed the airtightness test. If the product does not meet the airtightness performance index requirements, the water tank is leaking. Preferably, use a leak detector (or helium mass spectrometer) to locate the leak source and repair the leak.

[0083] The specific embodiments of the present invention disclosed above are intended to facilitate understanding and implementation of the present invention. Those skilled in the art will appreciate that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the embodiments disclosed in this specification; the scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A method for overlapping and sealing a water tank made of a high-rigidity carbon fiber composite material, characterized in that: The following steps are involved: Lay out the skin of the upper and lower boxes; Forming the composite ribs of the upper and lower boxes; The upper and lower boxes are formed by using their skin layers and composite stiffeners; Drill holes on the composite stiffener to form diversion ports; Lap and assemble the formed upper and lower boxes; Refine the appearance of the assembled upper and lower boxes; Conduct airtightness test on the assembled upper and lower boxes; The skin laying of the upper box body and the lower box body includes: The skin layers of the upper and lower boxes are mirror-symmetrical hierarchical structures centered on the foam sandwich layer. The ply layup order is: carbon fiber / medium-temperature epoxy plain fabric prepreg layer + carbon fiber / medium-temperature epoxy unidirectional prepreg layer + adhesive layer + foam sandwich layer + adhesive layer + carbon fiber / medium-temperature epoxy unidirectional prepreg layer + carbon fiber / medium-temperature epoxy plain fabric prepreg layer; The unidirectional prepreg in the skin layer of the upper and lower boxes is laid according to the quasi-isotropic rule. The unidirectional prepreg layers are not overlapped and only butted along the fiber direction. That is, the butt joint gap is parallel to the fiber direction and the butt joint gap width is ≤2mm. The overlap area of ​​the upper and lower boxes adopts a sunken staggered overlap structure, that is, a certain width of overlap area is reserved at the edges of the upper and lower boxes. The thickness of the foam sandwich layer laid in the overlapping area = (the thickness of the foam sandwich layer in the non-overlapping area - the sum of the thickness of the inner skin of the carbon fiber / medium-temperature epoxy unidirectional prepreg layer and the outer skin of the carbon fiber / medium-temperature epoxy unidirectional prepreg layer) / 2; the sinking depth of the overlapping area = the thickness of the foam sandwich layer in the non-overlapping area - the thickness of the foam sandwich layer in the overlapping area; The upper and lower boxes are formed by using the skin layers and composite stiffeners of the upper and lower boxes. A thermal expansion mold forming process is adopted. The upper and lower boxes are formed separately. The male module is composed of a metal core block and a rubber block. During the heating process, the male module expands to compress the rib position, and at the same time, downward pressure is applied to compress the skin of the box cavity to ensure the internal quality of each part.

2. The method according to claim 1, characterized in that The forming of the composite stiffeners of the upper box body and the lower box body includes: The structure of the composite stiffener is: carbon fiber / medium temperature epoxy unidirectional prepreg layer + adhesive layer + foam sandwich layer + adhesive layer + carbon fiber / medium temperature epoxy unidirectional prepreg layer; First, the raw materials are cut: 1) Foam is cut according to the envelope dimensions of the upper and lower fuel tank cavities; 2) Unidirectional prepreg is laid up in four layers (0 / +45 / 90 / -45) according to the quasi-isotropic rule, and the four layers of carbon fiber unidirectional prepreg are cut according to the cutting template design drawing; Then, an adhesive layer is evenly applied on the front and back sides of the foam, and a prepreg layer group is laid on the front and back sides of the foam. A vacuum bag is made, vacuum is evacuated, and an oven is used for curing to form a composite stiffener preform.

3. The method according to claim 1, characterized in that The method of forming the upper box body and the lower box body by using the skin layers and composite stiffeners of the upper box body and the lower box body comprises the following steps: (1) Fix the composite stiffeners, rubber blocks and metal core blocks: Place the metal core blocks in the mold in the order from front to back; Wrap the front and back of each composite stiffener with a layer of carbon fiber / medium temperature epoxy plain fabric prepreg, and leave a 30-40mm width of excess material on the peripheral edges, folding into a right angle to form a flange; While placing the core blocks, lay the composite stiffeners and rubber blocks in sequence, so that the flanges of the composite stiffeners are close to the inner surface of the corresponding box; (2) Mold closing: buckle the mold cover onto the mold, tighten the pressure bolts, and finally use the mold closing depth detection pin to check whether the mold is in place; (3) Oven curing: Place the mold in the oven and start heating it up. Keep the oven temperature at 100±5℃ and heat the mold to 70±5℃. Take the mold out of the oven. Tighten the mold pressure screws again. Check that the mold gap is ≤0.5mm. After passing the test, place the mold in the oven and keep the temperature at 170±5℃. When the mold temperature reaches 130±5℃, keep the temperature for 180min. After the holding time is over, the mold starts to cool down with the oven. When the oven temperature drops to 60℃, take the mold out of the oven and prepare for demoulding. (4) Demolding: After the product has been cured, unscrew the mold pressure bolts, remove the mold cover, take out the core block in the mold, clean the residual resin on the surface, remove the molding mold, and separate the product from the mold: (5) Finishing: Use fine sandpaper to polish off the small amount of burrs, edges, steps and wrinkles remaining on the inner and outer surfaces of the product to ensure smooth transition of each local area of ​​the inner surface of the upper box body and smooth closing of the upper and lower box covers of the fuel tank.

4. The method according to claim 1, wherein The drilling of holes on the composite stiffener is to evenly drill a number of through holes on the composite stiffener, the hole diameter of which is 20-30 mm. The composite stiffeners located at the highest point and the lowest point of the water tank need to be processed with through holes respectively to ensure that the horizontal filling and unloading capacity of the water tank are complete.

5. The method according to claim 1, wherein The overlapping and assembling of the formed upper box body and lower box body includes: Process water inlet and outlet on the surface of the upper box and lower box; Grind the joint area of ​​the upper and lower boxes into a rough surface, and use a scraper to evenly apply the adhesive to the joint area of ​​the upper and lower boxes; Place the lower box on the fixture platform, buckle the upper box onto the lower box steadily, ensure that the upper and lower boxes are tightly closed, so that the adhesive can obviously flow out from the bonding gap between the upper and lower boxes before pressurized curing, and then cure at room temperature or heat. After confirming that the overflowed adhesive has hardened, remove the upper and lower boxes from the fixture.

6. The method according to claim 1, characterized in that The finishing of the appearance of the assembled upper box body and the lower box body includes: polishing the cured glue on the outer surfaces of the upper box body and the lower box body to make the surface smooth and ensure the appearance quality.

7. The method according to claim 1, characterized in that The airtightness test of the assembled upper and lower boxes includes: The water inlet of the water tank is connected to the charging interface, and the water outlet is connected to the deflation interface, and switch valves are installed at the interfaces respectively; an air source device is installed at the charging interface position for inflating the box; a pressure gauge is installed at the deflation interface position to detect the real-time pressure value inside the box; Open the air inlet valve, close the air outlet valve, and fill the water tank with compressed air or helium with a concentration greater than 95%. Observe the pressure gauge reading while filling. When the reading reaches the index detection requirements, close the air inlet valve, disconnect the air source, and let it stand for 10 to 20 minutes. After the air pressure inside the box stabilizes, record the pressure gauge reading as the initial pressure value; maintain the pressure for the required time, and record the pressure gauge reading after completion as the end pressure value; also record the ambient temperature values ​​at the beginning and end, and convert the pressure leakage according to the Bernoulli equation; If the product meets the airtight performance index requirements, it means that the water tank air tightness test is qualified; if the product does not meet the airtight performance index requirements, there is a leak in the water tank. Use a leak detection liquid or a helium mass spectrometer to lock the leak source and repair the leak point.

8. A high-rigidity carbon fiber composite water tank formed according to the method according to any one of claims 1 to 7.

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