Mold and preparation method of small-size carbon fiber composite liquid hydrogen storage tank

Abstract

This invention discloses a mold and preparation method for a small-sized carbon fiber composite liquid hydrogen storage tank, belonging to the field of composite material preparation technology. It includes: preparing four water-soluble core mold units; sequentially connecting the four water-soluble core mold units circumferentially via circumferential limiting plates and connecting shafts to form an integral water-soluble core mold structure, and then locking the connection through a locking structure. The use of separate water-soluble core mold units results in smaller volume, more regular structure, and higher precision, effectively avoiding breakage during molding and improving the molding accuracy of small liquid hydrogen storage tanks. Simultaneously, the larger dissolution area during demolding effectively shortens demolding time and reduces the risk of water-soluble residue in the components. Furthermore, one end of the integral water-soluble core mold structure is securely connected via a cap, while the other end is locked via a locking structure on the connecting shaft, locking the water-soluble core mold in both the circumferential and axial directions, preventing phase or axial displacement of the water-soluble core mold, further improving molding accuracy.

Description

Technical Field

[0001] This invention relates to the mold and preparation method of a small-sized carbon fiber composite liquid hydrogen storage tank, belonging to the field of composite material preparation technology. Background Technology

[0002] Liquid hydrogen storage tanks are widely used in aerospace launch vehicles, cryogenic propulsion systems, and hydrogen energy storage and transportation. They are key equipment for the safe storage and supply of high-energy-density cryogenic media. As pressure vessels with ultra-low temperature and high reliability requirements, they have extremely high requirements for geometric consistency, interface quality, and assembly stability during the manufacturing process. Especially in the case of small-sized liquid hydrogen composite material storage tanks (usually referring to tanks with a volume of about 30-50L, a diameter of less than 300mm, and an opening of less than 80mm in the end cap area), the mold and tooling system directly determines the feasibility of integral molding and the level of failure risk.

[0003] Small-sized liquid hydrogen storage tanks are typically fabricated using rigid molds, which include monolithic rigid molds and detachable modular rigid molds. However, using this type of rigid mold presents the following problems: 1. Due to the limited internal space of small-sized liquid hydrogen storage tanks, the demolding path of integral rigid molds is restricted, making it difficult to achieve smooth demolding; detachable rigid molds require an increase in the number of blocks and locking connection structures to meet assembly and demolding needs, resulting in complex mold structure, high processing and assembly costs, and significant assembly errors, which in turn reduces the feasibility of one-time integral molding and affects the reuse of molds. 2. Small-sized liquid hydrogen storage tanks have poor internal visibility and accessibility. Mold alignment, positioning, and locking are completed within a limited space. Slight deviations may cause discontinuities, misalignments, or reference drift in the internal shape. At the same time, in the process related to molding / curing, it is difficult to obtain a stable and repeatable geometric reference and holding method for the positioning objects corresponding to the lining and end areas. Position deviations and assembly drifts are prone to occur, which increases the risk of interface defects, structural defects, and sealing failure. 3. Limited demolding path and poor reusability: integral hard molds often face the problem of being difficult to extract or remove; while segmented hard molds can be disassembled and demolded, the disassembly sequence is complicated, the operation window requirements are high, and the disassembly and assembly process is prone to mold wear or interference with the formed structure, thereby reducing the mold reuse rate, increasing manufacturing costs, and affecting the engineering realization of one-time integral forming of small-sized storage tanks.

[0004] To address the problems associated with using rigid molds to fabricate small-sized liquid hydrogen storage tanks, existing technologies employ water-soluble mandrels as an alternative. These mandrels are made using a matrix such as quartz sand or silica microspheres combined with a water-soluble adhesive (e.g., polyethylene glycol aqueous solution). After molding and curing, the mandrel is dissolved and separated to obtain the component, reducing the difficulty of demolding in confined spaces. However, the integral molds made with water-soluble mandrel materials are prone to deformation, cracking, porosity, and uneven density during casting, pressing, drying, and curing, affecting overall strength and making them susceptible to breakage during molding. Precision control is difficult, impacting the molding accuracy of small liquid hydrogen storage tanks. Furthermore, the circumferential fixing of the water-soluble mandrel relies heavily on end clamping and friction, lacking a unique circumferential reference like a keyway phase lock. This makes them susceptible to slight phase drift under external forces. Axial positioning is also primarily achieved through end clamping, lacking a clear axial locking structure, making them more prone to axial displacement under external loads or changes in clamping force, thus compromising molding accuracy. Summary of the Invention

[0005] To address the problems of easy breakage and cracking in current water-soluble mandrel molding processes, which affect strength, and the lack of circumferential and axial fixing structures, ultimately impacting molding accuracy, this invention provides a mold and preparation method for a small-sized carbon fiber composite liquid hydrogen storage tank. The technical solution is as follows: In a first aspect, the present invention discloses a mold for a small-sized carbon fiber composite liquid hydrogen storage tank. The mold includes: multiple water-soluble core mold units and a connecting shaft. The multiple water-soluble core mold units are inserted and connected to the connecting shaft through a circumferential limiting plate to assemble into a water-soluble core mold assembly. The outer end of the water-soluble core mold assembly is connected and positioned to the connecting shaft through a cap. The other end of the water-soluble core mold assembly, corresponding to the connecting shaft, is provided with a locking structure. The locking structure locks the water-soluble core mold assembly on the connecting shaft in the circumferential and axial directions.

[0006] Furthermore, the locking structure includes a circumferential limiting plate and an axial limiting plate. The inner sidewall of the circumferential limiting plate is provided with a keyway and an internal thread. The circumferential limiting plate is threadedly connected to the connecting shaft, and the connecting key on its keyway is circumferentially locked to the connecting shaft. The axial limiting plate is set against the circumferential limiting plate and is threadedly connected to the connecting shaft, thereby axially locking the circumferential limiting plate.

[0007] Furthermore, the specific mold used to prepare a single water-soluble core mold unit includes a main mold and a baffle mold. The baffle mold is detachably connected to the main mold. After the main mold is connected to the baffle mold, its inner cavity is a fan-shaped cavity. A central core mold is also provided at the top of the connection between the main mold and the baffle mold. The central core mold includes a small fan-shaped mold that matches its fan-shaped cavity. A rectangular mold is connected at the center of the lower end of the small fan-shaped mold.

[0008] Furthermore, a hollow bamboo is provided at the center of the specific mold. The hollow bamboo includes one or more and is arranged along the length of the fan-shaped cavity. The diameter of the hollow bamboo is 30-40mm and the length is 450-500mm.

[0009] Secondly, this invention discloses a method for preparing a mold for a small-sized carbon fiber composite liquid hydrogen storage tank, the method comprising: Step 1: Inject the water-soluble material into a specific mold, dry, compact, and demold to prepare four water-soluble core mold units in sequence; Step 2: Sequentially connect the four water-soluble core mold units to the connecting shaft along the circumferential direction via the circumferential limiting plate, and assemble them to form the main structure of the water-soluble core mold; Step 3: The main body structure of the water-soluble core mold is externally tightened and fixed with cloth tape; Step 4: Lay another layer of release cloth on the outer surface of the main structure of the water-soluble core mold to complete the preparation of the water-soluble core mold.

[0010] Furthermore, in step 1, the water-soluble material includes water-soluble core resin R323, toughening agent LF, and reinforcing filler quartz powder, in a mass ratio of: .

[0011] Furthermore, in step 1, the preparation process of the water-soluble core mold unit is as follows: First, add toughening agent LF to water-soluble core resin R323 and stir for 5-10 minutes. Then add quartz powder and stir for 10-15 minutes to obtain a uniform mixture. Next, add rubber balls to the mixture and stir evenly. The rubber balls have a particle size of 2-6 mm and are added at 5%-15% of the total volume of the mixture. After pre-coating the water-soluble core mold with release agent DH9719 and polishing it, pour the mixture in layers and tamp each layer. Then place it in an oven to heat and cure for 3-4 hours at a temperature greater than 100℃. After completion, demold.

[0012] Furthermore, in step 3, the fabric tape includes three strips, which are spaced apart on the outer peripheral surface of the water-soluble core mold body structure, and the fabric tape is bonded to the outside of the water-soluble core mold structure.

[0013] Furthermore, in step 4, the release cloth is laid manually, that is, the operator manually unfolds the release cloth along the outer surface of the water-soluble core mold body structure and lays it section by section, so that the release cloth adheres to the outer surface of the core mold, and eliminates wrinkles and air bubbles by compaction.

[0014] The beneficial effects of this invention are: By dividing the existing integral water-soluble core mold structure into multiple separate water-soluble core mold units, which are then prepared using specially designed molds and connected to the connecting shaft via circumferential limiting plates, the overall water-soluble core mold structure is assembled and connected. Using separate water-soluble core mold units results in smaller size, more regular structure, and higher precision, effectively avoiding breakage during molding and improving the molding accuracy of small liquid hydrogen storage tanks. Furthermore, the larger dissolution area during demolding effectively shortens demolding time and reduces the risk of water-soluble residue in the components. Additionally, one end of the overall water-soluble core mold structure is securely connected via a cap, while the other end is locked via a locking structure on the connecting shaft, locking the water-soluble core mold in both the circumferential and axial directions to prevent phase or axial displacement, further improving molding accuracy. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the mold structure according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the installation structure of the connecting shaft and the circumferential limiting plate in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of a specific mold according to Embodiment 1 of the present invention; Figure 4 This is an exploded view of a specific mold according to Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of a specific mold containing hollow bamboo as described in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the structure of the water-soluble core mold body structure wrapped with cloth tape according to Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of another direction of the water-soluble core mold body structure wrapped with cloth tape in Embodiment 2 of the present invention; Figure 8 This is a schematic diagram of the structure of the water-soluble core mold body structure with a release cloth laid on the outside, as shown in Embodiment 2 of the present invention. Figure 9 This is a partial structural diagram of the installation of the water-soluble core mold main body structure and the locking structure in Embodiment 2 of the present invention; Figure 10 This is the present invention. Figure 9 A schematic diagram of the structure after assembly with the front end cap component; In the picture: 1. Main mold; 2. Baffle mold; 3. Core mold; 4. Connecting shaft; 5. Limiting plate; 6. Circumferential limiting plate; 7. Axial limiting plate; 8. Fabric tape; 9. End cap. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0018] Example 1 See Figure 1 , Figure 2 As shown, a mold for a small-sized carbon fiber composite liquid hydrogen storage tank is provided. The mold includes multiple water-soluble core mold units and a connecting shaft 4. There can be four water-soluble core mold units, which are connected to the connecting shaft 4 in the circumferential direction through a circumferential limiting plate 5 to form a whole water-soluble core mold. The connecting shaft 4 can be a steel shaft. The outer end of the whole water-soluble core mold is connected and positioned to the connecting shaft 4 through a cap 9. The other end of the whole water-soluble core mold, corresponding to the connecting shaft 4, is provided with a locking structure. The locking structure locks the whole water-soluble core mold on the connecting shaft 4 in the circumferential and axial directions, effectively preventing the whole water-soluble core mold from shifting or drifting in the circumferential or axial directions.

[0019] Furthermore, the locking structure includes a circumferential limiting disc 6 and an axial limiting disc 7. The inner sidewall of the circumferential limiting disc 6 is provided with a keyway, and the inner sidewall of the circumferential limiting disc 6 is also provided with an internal thread. The circumferential limiting disc 6 is threadedly connected to the connecting shaft 4, and the connecting key on its keyway is circumferentially locked to the connecting shaft 4. The axial limiting disc 7 is set to press against the circumferential limiting disc 6 and is threadedly connected to the connecting shaft 4, so that the circumferential limiting disc 6 is axially locked.

[0020] Further, see Figure 3 , 4 As shown, a specific mold used to prepare a single water-soluble core mold unit includes a main body mold 1 and a baffle mold 2. The baffle mold 2 is detachably connected to the main body mold 1. After the main body mold 1 is connected to the baffle mold 2, its inner cavity is a fan-shaped cavity. A central core mold 3 is also provided at the top of the connection between the main body mold 1 and the baffle mold 2. The central core mold 3 includes a small fan-shaped mold that matches its fan-shaped cavity. A rectangular mold is connected at the center of the lower end of the small fan-shaped mold.

[0021] Furthermore, a hollow bamboo core is also provided at the center of the aforementioned specific mold, see [link / reference]. Figure 5As shown, the hollow bamboo includes one or more, arranged along the length of the fan-shaped cavity, with a diameter of 30-40mm and a length of 450-500mm.

[0022] Example 2 This embodiment provides a method for preparing a small-sized carbon fiber composite liquid hydrogen storage tank, the method comprising: Step 1: Inject the water-soluble material into a special mold for the water-soluble core mold unit, dry, compact, and demold, and prepare four water-soluble core mold units in sequence.

[0023] Specifically, the mold includes a main body mold 1 and a baffle mold 2. The baffle mold 2 is detachably connected to the main body mold 1. After connection, the baffle mold 2 has a fan-shaped cavity inside. A core mold 3 is provided at the top of the fan-shaped cavity corresponding to the connection between the baffle mold 2 and the main body mold 1. The core mold 3 includes a small fan-shaped mold that matches the top fan-shaped cavity. A rectangular mold is connected to the center of the lower end of the small fan-shaped mold. The water-soluble core mold unit prepared by this mold has a large arc surface on its outer end face and a small arc surface on its inner end face. A rectangular mounting groove is provided on the inner end face.

[0024] Specifically, the water-soluble materials include water-soluble core resin R323, toughening agent LF, and reinforcing filler quartz powder, in the following mass ratio: .

[0025] Furthermore, the specific fabrication process of the water-soluble core mold unit is as follows: First, add toughening agent LF to water-soluble core resin R323 and stir for 5-10 minutes. Then add quartz powder and stir for 10-15 minutes to obtain a uniform water-soluble material mixture. Next, add rubber particles to the mixture and stir evenly. The rubber particles have a particle size of 2-6 mm and are added at 5%-15% of the total volume of the mixture. Connect the baffle mold 2 of the water-soluble core mold to the main mold 1. After pre-coating the water-soluble core mold with release agent DH9719 and polishing it, pour the mixture into the interior of the water-soluble core mold in layers and compact each layer. Install the center mold 3 and ensure that the material around the center mold is compacted. Then place it in an oven for heating and curing for 3-4 hours. The heating temperature is >100℃, preferably about 130℃. When the pouring thickness is >50 mm, adjust the heating time by 1 hour for every 10 mm increase. After curing, open the mold cover and cool it to room temperature in an oven. Then demold the water-soluble core mold unit. The cured core mold unit has moisture-absorbing properties, so it needs to be dried and stored for later use.

[0026] The rubber particles remain within the water-soluble material as placeholders during the curing process of the water-soluble mandrel unit and are mechanically removed during subsequent demolding or pretreatment, thereby forming a uniformly distributed porous structure within the water-soluble mandrel. The functions of this structure include: First, by forming uniformly distributed pores within the mandrel, the specific surface area of ​​the water-soluble mandrel is effectively increased, allowing the water-soluble medium to act simultaneously from both the outer surface and the internal pore interface during dissolution, thus improving the overall dissolution rate; Second, the formed porous structure constructs interconnected or semi-interconnected permeation paths within the mandrel, enabling the water-soluble medium to enter the internal region of the mandrel more quickly, reducing the time delay caused by layer-by-layer dissolution from the outside in; Third, the size and amount of the rubber microspheres are controllable, achieving improved dissolution efficiency while ensuring the integrity and mechanical strength of the mandrel unit.

[0027] Furthermore, during the fabrication of a single water-soluble core mold unit, a hollow bamboo is placed at the center of a specific mold. One or more hollow bamboo stalks can be used, see [reference needed]. Figure 3 As shown, hollow bamboo is evenly arranged along the length of the fan-shaped cavity. The diameter of the hollow bamboo is 30-40mm and the length is 450-500mm.

[0028] The main functions of this hollow bamboo are as follows: First, the water-soluble core mold unit is relatively thick. If hollow bamboo is used to occupy the middle, the thickness of the water-soluble core mold is kept less than 20 mm. In this way, during the heating and curing process, the water-soluble core mold is relatively thin, which can prevent cracking caused by the surface temperature of the core mold rising while the center is difficult to heat up. Second, the water-soluble core mold unit is slender and easy to break along its length. After adding hollow bamboo, the bamboo provides rigidity along its length, preventing the core mold unit from breaking. Finally, the hollow bamboo is used to form a guiding / draining channel or an auxiliary dissolution path in the subsequent dissolution process, thereby improving the feasibility and efficiency of water-soluble demolding.

[0029] Step 2, see Figure 1 As shown, the connecting shaft 4 and the water-soluble mandrel unit are assembled and installed. One end of the connecting shaft 4 is mounted on a winding machine or rotary device, and then four circumferential limiting plates 5, evenly distributed around the circumference of the connecting shaft 4, are inserted and fixed. The four water-soluble mandrel units are then sequentially inserted and connected to the circumferential limiting plates of the connecting shaft 4 via rectangular mounting slots along their circumference. The outermost layer is limited by a metal end cap, assembling to form the main structure of the water-soluble mandrel.

[0030] Step 4, see Figure 6 , Figure 7As shown, the water-soluble core mold body structure is circumferentially tightened and fixed by wrapping with spaced fabric tapes. The fabric tapes 8 include three strips, which are respectively arranged on the outer circumferential surface of the water-soluble core mold body structure. The fabric tapes are self-adhesive fabric tapes with a pressure-sensitive adhesive layer on their inner surface, and are bonded to the outer surface of the water-soluble core mold body structure by pressing.

[0031] Step 5, see Figure 8 As shown, a release liner is then laid on the outer surface of the water-soluble core mold body structure. The release liner should adhere to the outer surface of the core mold and eliminate uneven defects such as wrinkles and air bubbles. If necessary, it can be laid in sections along the axial direction and the overlaps should be compacted to ensure the flatness and continuity of the outer surface of the core mold, thus completing the preparation of the water-soluble core mold. Specifically, the release liner is laid manually, segment by segment along the axial direction of the water-soluble core mold body structure, so that the release liner completely covers the outer surface of the water-soluble core mold body structure. The release liner is a self-adhesive release liner with a pressure-sensitive adhesive layer on its inner surface, which is adhered and fixed to the outer surface of the water-soluble core mold body structure by pressing.

[0032] Further, see Figure 9 As shown, a locking structure is provided on the connecting shaft 4 near the end that is integrally connected to the water-soluble mandrel. This locking structure includes a circumferential limiting disc 6 and an axial limiting disc 7. The inner wall of the circumferential limiting disc 6 has a keyway and an internal thread. During assembly, the key block is simultaneously embedded in the grooves of the connecting shaft 1 and the circumferential limiting disc 4, achieving circumferential locking of the circumferential limiting disc 6 relative to the connecting shaft 1. At the same time, the flange of the circumferential limiting disc 7 is connected to the front end member with bolts and tightened to prevent the circumferential limiting disc 4 from rotating circumferentially relative to the flange, thus establishing a unique circumferential phase reference. The axial limiting disc 7 is passed through the connecting shaft 1, and its inner ring surface thread is screwed into the thread on the outer surface of the connecting shaft 1, tightened until the end face of the axial limiting disc 7 abuts against the circumferential limiting disc 6 to form an axial stop, restricting the circumferential limiting disc 6 from axially translating along the connecting shaft 1 and stabilizing the axial reference. See also Figure 10 As shown, the locking structure is designed to prevent the water-soluble core mold from sliding circumferentially and axially after the front end cap is installed during the fabrication of the small liquid hydrogen storage tank, thus ensuring the stability of the fabrication process.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A mold for a small-sized carbon fiber composite liquid hydrogen storage tank, characterized in that, The mold includes: The mold includes: multiple water-soluble core mold units and a connecting shaft. The multiple water-soluble core mold units are inserted and connected to the connecting shaft through a circumferential limiting plate to assemble into a water-soluble core mold assembly. The outer end of the water-soluble core mold assembly is connected and positioned to the connecting shaft through a cap. The other end of the water-soluble core mold assembly, corresponding to the connecting shaft, is provided with a locking structure. The locking structure locks the water-soluble core mold assembly on the connecting shaft in the circumferential and axial directions.

2. The mold according to claim 1, characterized in that, The locking structure includes a circumferential limiting plate and an axial limiting plate. The inner sidewall of the circumferential limiting plate is provided with a keyway and an internal thread. The circumferential limiting plate is threadedly connected to the connecting shaft, and the connecting key on its keyway is circumferentially locked to the connecting shaft. The axial limiting plate is set against the circumferential limiting plate and is threadedly connected to the connecting shaft, so that the circumferential limiting plate is axially locked.

3. The mold according to claim 2, characterized in that, A specific mold for preparing a single water-soluble core mold unit includes a main mold and a baffle mold. The baffle mold is detachably connected to the main mold. After the main mold is connected to the baffle mold, its inner cavity is fan-shaped. A central core mold is also provided at the top of the connection between the main mold and the baffle mold. The central core mold includes a small fan-shaped mold that matches its fan-shaped cavity. A rectangular mold is connected at the center of the lower end of the small fan-shaped mold.

4. The mold according to claim 3, characterized in that, Hollow bamboo is also provided at the center of the specific mold. The hollow bamboo includes one or more and is arranged along the length of the fan-shaped cavity. The diameter of the hollow bamboo is 30-40mm and the length is 450-500mm.

5. A method for preparing a mold for a small-sized carbon fiber composite liquid hydrogen storage tank, wherein the mold is prepared based on the mold described in claims 1 to 4, characterized in that, The method includes: Step 1: Inject the water-soluble material into a specific mold, dry, compact, and demold to prepare four water-soluble core mold units in sequence; Step 2: Sequentially connect the four water-soluble core mold units to the connecting shaft along the circumferential direction via the circumferential limiting plate, and assemble them to form the main structure of the water-soluble core mold; Step 3: The main body structure of the water-soluble core mold is externally tightened and fixed with cloth tape; Step 4: Lay another layer of release cloth on the outer surface of the main structure of the water-soluble core mold to complete the preparation of the water-soluble core mold.

6. The method according to claim 5, characterized in that, In step 1, the water-soluble material includes water-soluble core resin R323, toughening agent LF, and reinforcing filler quartz powder, with a mass ratio of R323:LF:quartz powder = 100:20:1000.

7. The method according to claim 6, characterized in that, In step 1, the preparation process of the water-soluble core mold unit is as follows: First, add toughening agent LF to water-soluble core resin R323 and stir for 5-10 minutes. Then add quartz powder and stir for 10-15 minutes to obtain a uniform mixture. Next, add rubber balls to the mixture and stir evenly. The rubber balls have a particle size of 2-6 mm and are added at 5%-15% of the total volume of the mixture. After pre-coating the water-soluble core mold with release agent DH9719 and polishing it, pour the mixture in layers and tamp each layer. Then place it in an oven to heat and cure for 3-4 hours at a temperature greater than 100℃. After completion, demold.

8. The method according to claim 5, characterized in that, In step 3, the fabric tape includes three strips, which are arranged at intervals on the outer peripheral surface of the water-soluble core mold body structure, and the fabric tape is bonded to the outside of the water-soluble core mold structure.

9. The method according to claim 5, characterized in that, In step 4, the release cloth is laid manually, that is, the operator manually unfolds the release cloth along the outer surface of the water-soluble core mold body structure and lays it section by section, so that the release cloth adheres to the outer surface of the core mold, and eliminates wrinkles and air bubbles by compaction.

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