Preparation method of polyimide-modified and resin-filled rocket engine casing

Abstract

The present invention provides a method for preparing a polyimide-modified and resin-filled rocket engine casing. The method comprises the following steps: preparing a polyamic acid solution, adding montmorillonite and polyethylene glycol to the polyamic acid solution to form a modified polyamic acid mixed solution; pouring the modified polyamic acid mixed solution into a dipping tank, passing the fiber bundle through the dipping tank to form a prepreg, and heating the prepreg to remove the organic solvent; providing an insulating layer on the surface of a sand core mold, wrapping the heated prepreg around the insulating layer, and demolding to obtain a semi-finished casing; extruding the semi-finished casing and filling it with the modified polyamic acid mixed solution to eliminate interstitial spaces between the fibers in the semi-finished casing; and heating and curing the semi-finished casing after the voids have been removed to cause an imidization reaction of the polyamic acid to form polyimide, thereby obtaining a polyimide-modified and resin-filled rocket engine casing. The present invention can produce a rocket engine casing with good airtightness and minimal voids in the fiber layer.

Description

Technical Field

[0001] The invention belongs to the technical field of rocket engine casings, and in particular relates to a method for preparing a polyimide-modified and resin-filled rocket engine casing. Background Art

[0002] China is currently vigorously developing its aerospace industry, and rocket engines, as core components of rockets, play a crucial role. The rocket engine casing not only houses the propellant charge but also serves as a pressure vessel that withstands significant loads, making it crucial. Because it lacks an inner lining, rocket engine casings are more susceptible to gas permeation and leakage. Combustion of gunpowder within the casing releases gas, effectively rapidly inflating and deflating the casing. Gas permeation can easily create a pressure differential, causing the casing to buckle and deform, leading to damage. Furthermore, voids can form during the manufacturing process of rocket engine casings due to various factors and imperfect process implementation. These voids significantly impact material quality and mechanical properties, providing pathways for air and moisture to diffuse into the casing, leading to polymer degradation and oxidation, and weakening the interfacial bonding between the fiber and matrix, ultimately impacting the composite's interlaminar shear strength, flexural strength, modulus, tensile strength, compressive strength, modulus, fatigue resistance, and high-temperature performance. To address the issues of gas permeation and voids in the fiber layers of rocket engine casings during manufacturing, a new manufacturing method for rocket engine casings is urgently needed. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing a rocket engine casing with a polyimide modified fiber layer and resin filling the gaps in the fiber layer.

[0004] The technical solution for achieving the purpose of the present invention is: a method for preparing a polyimide-modified and resin-filled rocket engine casing, comprising the following steps:

[0005] Step (1): preparing a polyamic acid solution, adding 25±2% by mass of montmorillonite and 5±0.5% by mass of polyethylene glycol to the polyamic acid solution to form a modified polyamic acid mixed solution;

[0006] Step (2): pouring the modified polyamic acid mixed solution prepared in step (1) into a dipping tank, passing the fiber bundle through the dipping tank to form an impregnated material, and heating the impregnated material to remove the organic solvent;

[0007] Step (3): a heat-insulating layer is provided on the surface of the sand core mold, the impregnated material heated in step (2) is wrapped around the heat-insulating layer, and demoulding is performed to obtain a semi-finished shell;

[0008] Step (4): extruding the shell semi-finished product and filling it with the modified polyamic acid mixed solution of step (1), thereby removing the gaps between the fibers of the shell semi-finished product;

[0009] Step (5): The shell semi-finished product after the voids are removed in step (4) is heated and cured, so that the polyamic acid undergoes an imidization reaction to generate polyimide, thereby obtaining a polyimide-modified and resin-filled rocket engine shell.

[0010] Furthermore, the polyamic acid solution is prepared in step (1) as follows:

[0011] Using N,N-dimethylacetamide as an organic solvent, 1,2,4,5-pyromellitic dianhydride is added to N,N-dimethylacetamide while stirring. After dissolution, 4,4'-diaminodiphenyl ether is added in batches at an equal molar ratio to 1,2,4,5-pyromellitic dianhydride while stirring continuously to form a polyamic acid solution with a concentration of 10±2%.

[0012] Furthermore, when montmorillonite and polyethylene glycol are added in step (1), mechanical stirring is required, the stirring speed is 1000-1200 r / min, and the stirring is continued for 10-15 minutes.

[0013] Furthermore, the fiber bundle used in step (2) is a carbon fiber bundle, and the fiber bundle passes through the dipping tank transversely at a transverse speed of 0.5 to 1 m / min. The heating temperature in step (2) is 50 to 100°C.

[0014] Furthermore, the winding method in step (3) is circumferential winding and / or spiral winding.

[0015] Furthermore, step (3) is specifically as follows: the insulation layer cut into sheets is glued to the surface of the core mold piece by piece, and then the polyamic acid prepreg is pre-set with a set tension and then wound according to the winding method and sequence obtained by the optimized layup.

[0016] Furthermore, the void removal device used in step (4) includes a glue injection tube, a sealed bag, a steel tube, a thermal expansion rubber, a rubber cover and a glue extraction tube;

[0017] During operation, the shell semi-finished product with internal sealing filled with heat-expanding rubber is placed in a sealing bag, one end of the sealing bag is connected to a glue injection hose and the other end is connected to a glue extraction hose, the sealing bag is placed in a steel pipe, the glue injection hose is injected with a modified polyamic acid mixed solution, and the glue extraction hose continuously extracts the modified polyamic acid mixed solution, allowing the mixed polyamic acid mixed solution to fill the sealed bag, maintaining the pressure in the bag at a negative pressure of 0.5±0.1Mpa, heating to 100-150°C, keeping the temperature constant for 15-30 minutes, and then cooling to room temperature; demolding, taking out the shell semi-finished product with the gaps removed.

[0018] Furthermore, interfaces are provided at both ends of the sealing bag, and the glue injection hose, glue extraction hose and the interfaces are connected by threads; the diameters of the glue injection hose and glue extraction hose are 1 / 5 to 1 / 4 of the diameter of the engine casing, the volume of the sealed bag is 1.2 to 1.3 times the volume of the engine casing, and the radius is 7 to 10 mm larger than the radius of the engine casing; the length of the steel pipe is 50 to 100 cm larger than the engine barrel section, the engine casing is aligned with the middle of the steel pipe, the radius of the steel pipe is 4 to 6 mm larger than the engine casing, the thermal expansion rubber fills the inner cavity of the engine casing, and rubber covers are installed at both ends of the engine casing using screws and glue is added around the screws to seal.

[0019] Furthermore, the heating and curing in step (5) is a step-by-step heating process, specifically: heating to 100°C for 1 hour, heating to 150°C for 1 hour, heating to 200°C for 1 hour, heating to 250°C for 2 hours, heating to 300°C for 2 hours, and finally cooling to room temperature.

[0020] A polyimide-modified and resin-filled rocket engine casing is prepared by the above method.

[0021] Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) The present invention proposes a method for modifying polyimide resin through analysis and proposes a ratio of co-modification of montmorillonite and polyethylene glycol, which can effectively improve the gas barrier performance of the resin by more than 50% while ensuring the mechanical properties;

[0023] (2) The present invention uses void removal equipment and technology to fill the voids in the fiber layer and extract bubbles, thereby reducing the void content in the fiber layer, reducing the possibility of cracks in the shell, and increasing the strength.

[0024] (3) By modifying and removing voids, the present invention can produce a rocket engine casing with good airtightness and few voids in the fiber layer, resulting in higher strength and greater stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the schematic diagram of polyimide modification.

[0026] Figure 2 This is a structural diagram of the rocket engine casing.

[0027] Figure 3 Diagram of the structure of the gap removal equipment. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings.

[0029] After analysis, the present invention proposes a method for modifying polyimide to enhance airtightness. The proposed co-modification ratio of montmorillonite and polyethylene glycol effectively prevents gas permeation while maintaining mechanical properties. By adding montmorillonite, a high-specific-surface-area material, as a gas barrier, the diffusion path of gas molecules in the resin is extended, reducing its gas diffusion coefficient. However, montmorillonite aggregates are incompatible with the resin, which can significantly reduce the resin's mechanical properties. Therefore, polyethylene glycol is further added as a modifier. At room temperature, polyethylene glycol is a flexible, macromolecular chain. The addition of polyethylene glycol increases the distance between the polyimide's molecular chains and reduces intermolecular forces. Consequently, the polyimide's toughness is increased. However, the addition of polyethylene glycol reduces the resin's airtightness, making the co-modification ratio of montmorillonite and polyethylene glycol crucial. The present invention proposes a co-modification ratio that improves gas barrier properties by over 50%.

[0030] After analysis, the present invention proposes a device and process for removing voids in the fiber layer of a rocket engine casing, thereby reducing voids in the fiber layer. Research has shown that the voids mainly fall into the following categories: voids in the tow impregnation material, voids at the edges of the tow impregnation material, curling voids, overlapping voids, voids in the tow impregnation material, and voids between layers. The present invention uses a steel pipe outside a sealed bag with thermally expanded rubber to squeeze the fiber layer, expel the air in the voids in the fiber layer, and extract the bubbles along with the solution by extracting the solution. When the rubber shrinks, the voids reappear, and the voids are filled with the modified solution by introducing the modified solution, thereby reducing voids in the fiber layer. Removing voids using this method can reduce voids by more than 60% and reduce the possibility of cracks.

[0031] The method for preparing a rocket engine casing with a polyimide-modified fiber layer and resin-filled voids in the fiber layer provided in an embodiment of the present invention specifically comprises the following steps:

[0032] Step 1: First, prepare 1,2,4,5-pyromellitic dianhydride (2180g) and 4,4'-diaminodiphenyl ether (2000g) in a molar ratio of 1:1, heat to 150℃ and dry for 2h, then take 12.9LN,N-dimethylacetamide and distill it and treat it with magnesium powder for 2h to remove a small amount of water inside. First add the organic solvent to the container, turn on the agitator, the agitator speed is 150r / min, add dianhydride, after the dianhydride is dissolved, add diamine in 5 batches, with an interval of 15min between each addition, and continue stirring for 2h to form a polyamic acid mixed solution with a concentration of 10%.

[0033] Step 2: Add 4250 g of montmorillonite and 850 g of polyethylene glycol, and stir at 1000 r / min for 10 min until completely dissolved.

[0034] Step 3: Use a special fiber spreading device to unfold the T70012K unidirectional fiber bundle, and continuously impregnate the fiber with polyamic acid solution at a pre-impregnation speed of 0.5m / min.

[0035] Step 4: Heat the impregnated material at 80°C to remove the remaining organic solvent;

[0036] Step 5: First, install the sand core mold on the wrapping machine fixture. Then, glue the cut insulation sheets one by one onto the core mold surface. Then, after setting a certain tension, wrap the polyamic acid prepreg around the insulation layer with two layers of hoop wrap, then two layers of spiral wrap, and then two layers of hoop wrap. Repeat this four times, and then remove from the mold. The wrapping method and sequence here are derived from the layer optimization.

[0037] Step 6: Place the fiber-wound structure on the workbench, install the thermal expansion rubber, use screws to install the rubber covers of the left and right interfaces, apply sealant on the screws, wait for the sealant to solidify, put the sealed fiber-wound structure into a sealing bag, and place it in the steel pipe, ensuring that the length of the steel pipe covers the barrel section, install the injection hose and the extraction hose, close the extraction hose, inject air through the injection hose, perform an airtightness test, use ultrasound to remove bubbles from the above-mentioned modified mixed solution, connect the injection hose to the modified mixed solution with bubbles removed, and use the extraction hose to extract the modified mixed solution, so that the mixed modified solution fills the sealed bag and maintains a negative pressure of 0.5 MPa. Slowly heat the temperature to 100°C, keep the temperature constant for 15 minutes, slowly cool to room temperature, take out the fiber-wound structure with the gaps removed, place it on the workbench, open the rubber cover, and take out the thermal expansion rubber.

[0038] Step 7: Place the engine casing with the gaps removed above into a curing oven for heating and curing. First, install the engine casing on the tooling, keep rotating, and heat it step by step. Heat it to 100℃ for 1 hour, then to 150℃ for 1 hour, then to 200℃ for 1 hour, then to 250℃ for 2 hours, then to 300℃ for 2 hours, and finally slowly cool it to room temperature.

Claims

1. A method for preparing a polyimide-modified and resin-filled rocket engine casing, characterized in that: The steps include: Step (1): preparing a polyamic acid solution, adding 25±2% by mass of montmorillonite and 5±0.5% by mass of polyethylene glycol to the polyamic acid solution to form a modified polyamic acid mixed solution; Step (2): pouring the modified polyamic acid mixed solution prepared in step (1) into a dipping tank, passing the fiber bundle through the dipping tank to form an impregnated material, and heating the impregnated material to remove the organic solvent; Step (3): a heat-insulating layer is provided on the surface of the sand core mold, the impregnated material heated in step (2) is wrapped around the heat-insulating layer, and the mold is demoulded to obtain a semi-finished shell; Step (4): extruding the semi-finished shell product and filling it with the modified polyamic acid mixed solution of step (1), thereby removing the gaps between the fibers of the semi-finished shell product; Step (5): heating and curing the shell semi-finished product after removing the gap in step (4), so that the polyamic acid undergoes imidization reaction to generate polyimide, thereby obtaining a polyimide-modified and resin-filled rocket engine shell; The polyamic acid solution is prepared in step (1) as follows: Using N,N-dimethylacetamide as an organic solvent, 1,2,4,5-pyromellitic dianhydride is added to 1N,N-dimethylacetamide while stirring. After dissolution, 4,4'-diaminodiphenyl ether is added in batches at an equal molar ratio to 1,2,4,5-pyromellitic dianhydride while continuing to stir to form a polyamic acid solution with a concentration of 10±2%.

2. The method according to claim 1, characterized in that When adding montmorillonite and polyethylene glycol in step (1), mechanical stirring is required at a stirring speed of 1000-1200 r / min and the stirring is continued for 10-15 minutes.

3. The method according to claim 2, characterized in that The fiber bundle used in step (2) is a carbon fiber bundle, and the fiber bundle passes through the dipping tank transversely at a transverse speed of 0.5~1m / min. The heating temperature in step (2) is 50~100℃.

4. The method according to claim 3, characterized in that The winding method in step (3) is hoop winding and / or spiral winding.

5. The method according to claim 4, characterized in that Step (3) is specifically as follows: the insulation layer cut into sheets is glued to the surface of the core mold piece by piece, and then the polyamide acid prepreg is pre-set with a set tension and then wound according to the winding method and sequence obtained by the optimized layup.

6. The method according to claim 5, characterized in that The device for removing the gap used in step (4) comprises a glue injection tube (1), a sealed bag (3), a steel tube (4), a thermal expansion rubber (5), a rubber cover (7) and a glue extraction tube (8); During operation, the semi-finished shell with internal sealing filled with heat expansion rubber (5) is placed in a sealing bag (3), one end of the sealing bag (3) is connected to the injection tube (1), and the other end is connected to the extraction tube (8), the sealing bag (3) is placed in the steel pipe (4), the injection tube (1) is injected with the modified polyamic acid mixed solution, and the extraction tube (8) continuously extracts the modified polyamic acid mixed solution, so that the mixed polyamic acid mixed solution fills the sealed bag (3), the pressure in the bag is maintained at a negative pressure of 0.5±0.1Mpa, heated to 100~150℃, kept at a constant temperature for 15~30min, and then cooled to room temperature; Demould and take out the semi-finished shell with the gap removed.

7. The method according to claim 6, characterized in that The sealing bag (3) is provided with interfaces (2) at both ends, and the glue injection tube (1), the glue extraction tube (8) and the interfaces are connected by threads; the diameters of the glue injection tube (1) and the glue extraction tube (8) are 1 / 5 to 1 / 4 of the diameter of the engine casing, the volume of the sealing bag (3) is 1.2 to 1.3 times the volume of the engine casing, and the radius is 7 to 10 mm larger than the radius of the engine casing; the length of the steel pipe (4) is 50 to 100 cm larger than the engine barrel section, the engine casing is aligned with the middle of the steel pipe, the radius of the steel pipe is 4 to 6 mm larger than the engine casing, the thermal expansion rubber (5) fills the inner cavity of the engine casing, and the rubber covers (7) are installed on both ends of the engine casing using screws and glue is added around the screws to seal.

8. The method according to claim 7, characterized in that The heating curing in step (5) is a step-by-step heating process, specifically: heating to 100°C for 1 hour, heating to 150°C for 1 hour, heating to 200°C for 1 hour, heating to 250°C for 2 hours, heating to 300°C for 2 hours, and finally cooling to room temperature.

9. A polyimide-modified and resin-filled rocket engine casing, characterized in that: The method according to any one of claims 1 to 8 is used for preparation.

Images