Precision molding and high-strength bonding method for bidirectional pressure-bearing plugging cover of rocket nozzle

Abstract

The present invention discloses a method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cap for a rocket nozzle, which relates to the field of rocket nozzle manufacturing technology. First, T1000-grade carbon fiber reinforced boron-modified phenolic resin prepreg is laid in a [0° / ±45° / 90°] 4S layer, and then hot-pressed and cured at 190°C and 4MPa for 2.5 hours to form a matrix with specific performance. Then, hydrogenated nitrile rubber and polytetrafluoroethylene are mixed and graphene is added to form an elastic sealing layer. The matrix is ​​plasma-treated and coated with a modified epoxy resin to form a transition layer. The matrix is ​​then subjected to zone heating and pressure-maintaining molding through a three-layer precision mold. The nozzle surface is then chemically plated with nickel-phosphorus and coated with a modified phenolic adhesive, which is then laser-positioned and cured for assembly. Finally, the method is strengthened through post-processing such as high-low temperature cycling. The present invention improves the bidirectional pressure-bearing capacity of the plugging cap and extends its aging life to 15 years. It solves the problems of interface debonding and high-temperature ablation of traditional plugging caps, meets the requirements of extreme environments ranging from -60°C to +200°C, and provides a highly reliable sealing solution for rocket launches.

Description

Technical Field

[0001] The present invention relates to the technical field of rocket nozzle manufacturing, and in particular to a method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle. Background Art

[0002] The performance of the rocket nozzle plug is a key sealing component of the space launch system, and its performance directly affects the reliability and safety of the rocket. Traditional plugs are mostly made of a single material by compression molding. Although carbon fiber reinforced resin-based composite materials have certain strength, they are prone to interface debonding problems under bidirectional pressure conditions. For example, the probability of sealing failure of existing one-way pressure plugs increases significantly when the positive pressure exceeds 6MPa, and structural damage is more likely to occur under reverse negative pressure conditions, which cannot meet the needs of the new generation of launch vehicles for complex pressure environments. In addition, the traditional molding process is difficult to control the interface bonding accuracy of multi-layer materials, resulting in microcracks in the plug due to mismatch of thermal expansion coefficients during the temperature cycle of -40℃~+150℃, and the leakage rate often exceeds , cannot pass the aerospace-grade sealing test.

[0003] The bonding technology for the plugging cap and nozzle has significant shortcomings. Traditional phenolic resin adhesives are prone to carbonization at high temperatures. When the nozzle temperature exceeds 300°C, the shear strength of the bond drops by over 50%. Furthermore, the adhesive cannot withstand the intense vibrations experienced during rocket launch (frequency 20-2000Hz, acceleration 30g). Furthermore, the existing assembly process relies on manual application of glue, resulting in a thickness uniformity deviation exceeding ±0.1mm, leading to a coaxial error of the plugging cap exceeding 0.5mm. This easily generates eccentric load stresses under high-pressure erosion, causing localized seal failure.

[0004] The lack of post-processing technology limits the environmental adaptability of the plug. Traditional plugs have not undergone systematic high and low temperature cycle treatment. The interface bonding strength decreases by more than 30% under extreme temperature differences, and the sealing performance retention rate in hot and humid environments is less than 85%. Due to the insufficient aging resistance of the plug, the leakage rate of a deep space exploration rocket increased to 100% after 6 months of storage. , forced to replace parts in advance. In addition, existing detection technology cannot effectively identify 0.5mm 2 The following micro-defects: a certain model of rocket plugging cover missed the detection of tiny delamination during X-ray inspection, resulting in sudden leakage during launch, becoming an important cause of space accidents. Summary of the Invention

[0005] The present invention proposes a method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle to solve the problems mentioned in the above-mentioned prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle comprises the following steps:

[0008] S1: Plug base molding step: Use T1000 grade carbon fiber reinforced boron modified phenolic resin prepreg, the ply angle is designed according to the [0° / ±45° / 90°] 4S cycle symmetry, and cure it at 190℃ and 4MPa pressure for 2.5 hours through isothermal hot pressing process to form a 220MPa tensile strength and thermal expansion coefficient ≤2×10 -6 / ℃ plugging substrate;

[0009] S2: Preparation of elastic sealing layer: Hydrogenated nitrile rubber and polytetrafluoroethylene powder were mixed in a mass ratio of 7:3, 2% graphene nanosheets, 0.5% nanosilica, and 1% vulcanizing agent DCP were added, and the mixture was kneaded at 155°C for 15 minutes using a twin-screw extruder, and then calendered into a 1.0 mm thick elastic sealing layer.

[0010] S3: Transition layer treatment step: Plasma treatment is performed on the surface of the blocking substrate to form a slightly rough surface with Ra = 4.5μm; a modified epoxy resin transition layer is applied and cured at 120°C for 1.5 hours. The shear strength between the transition layer and the substrate is 28MPa;

[0011] S4: Compression molding step: Place the plugging and capping substrate, transition layer, and elastic sealing layer into the mold in sequence, maintain the pressure at 2 MPa for 45 minutes, and create microchannels with a width of 0.08 mm and a depth of 0.04 mm on the mold surface to ensure gas discharge during the molding process;

[0012] S5: Plug cap assembly and bonding steps: Apply modified phenolic resin adhesive to the nozzle mounting surface using a spiral coating process. Use laser positioning technology to ensure that the coaxial error between the plug cap and the nozzle is less than 0.08mm. Curing at 150°C and 0.6MPa pressure for 4.5 hours. The axial tensile strength of the plug cap and nozzle is 18MPa.

[0013] S6: Post-processing strengthening step: the formed plugging cover is subjected to high and low temperature cycle treatment, followed by wet heat aging treatment and radiation irradiation treatment;

[0014] S7: Performance testing steps: X-ray inspection and water pressure test are performed on the plug cover. Acoustic emission detection technology is used to monitor stress changes. The stress-time evaluation formula is introduced: , S is the actual stress borne by the plugging cover, F(t) is the pressure value, A is the stress-bearing area of ​​the plugging cover, and λ is the correction coefficient.

[0015] Furthermore, 3% by mass of carbon nanotubes were added to the elastic sealing layer and evenly dispersed by a shear disperser to increase the thermal conductivity of the elastic sealing layer to The compression permanent deformation rate at a high temperature of 200°C is ≤15%, and the volume change rate of the medium immersion resistance is controlled within ±3%.

[0016] Furthermore, a core-shell structure toughener with a mass fraction of 8% is added to the modified epoxy resin of the transition layer, the core is butadiene rubber, and the shell is methyl methacrylate. A gradient coating process is adopted: the bottom layer is coated with a dilute solution containing 3% silane coupling agent and a solid content of 40%; the middle layer is coated with a standard solution containing 6% silane coupling agent and a solid content of 60%; the surface layer is coated with a concentrated solution containing 10% silane coupling agent and a solid content of 80%. An innovative formula correlating shear strength and number of cycles is introduced: , where S is the shear strength after N cycles, is the initial shear strength; k is the strength attenuation coefficient, which is determined according to the material properties; N is the number of cycles.

[0017] Furthermore, in the compression composite molding step, the mold adopts a segmented structural design, consisting of an inner core mold, a middle mold sleeve and an outer mold sleeve. The inner core mold is made of H13 hot working die steel, the middle mold sleeve is made of 4Cr5MoSiV1 steel, and the outer mold sleeve is made of 45 steel. An interference fit is adopted between the three-layer mold, and a micro-groove array with a depth of 0.03mm and a width of 0.05mm is processed on the mold surface. The micro-grooves are spaced 1mm apart and distributed in a honeycomb shape, so that excess resin can be discharged through the micro-grooves during the molding process.

[0018] Furthermore, in the step of assembling and bonding the plugging cover, the nozzle mounting surface is sandblasted before the adhesive is applied to form a rough surface with Ra=6.3μm, and then chemically plated with nickel-phosphorus alloy. After plating, it is heat treated at 400℃ for 1 hour to increase the bonding strength between the adhesive and the nozzle to 20MPa; a double-helix coating process is adopted, and the coating thickness uniformity deviation is ≤±0.02mm; vacuum-assisted exhaust technology is used during the assembly process to form a negative pressure environment of -0.08MPa between the nozzle and the plugging cover to discharge bubbles in the adhesive layer and make the porosity of the adhesive layer less than 1%.

[0019] Furthermore, in the post-treatment strengthening step, the high and low temperature cycle treatment adopts a combination of liquid nitrogen spray cooling and infrared radiation heating to generate controllable micro-stress inside the plugging cover; after the wet heat aging treatment, supercritical carbon dioxide extraction treatment is carried out to remove small molecular substances remaining inside the plugging cover; after the irradiation treatment, microwave annealing treatment is carried out to eliminate free radicals generated by the irradiation and restore the material properties.

[0020] Furthermore, in the performance testing step, ultrasonic C-scan detection technology is used to perform a full-size scan of the interior of the plugging cover; the water pressure test adopts a step-by-step loading method, and the strain distribution of the plugging cover is monitored simultaneously. When the pressure reaches the design value, the maximum strain of the plugging cover is ≤0.3%; laser holographic interference technology is used to detect the deformation of the plugging cover under pressure.

[0021] Furthermore, in the carbon fiber prepreg of the plugging matrix, the volume fraction of carbon fiber is controlled at 65%±1%, the resin system adopts boron-modified phenolic resin, and 2% ferrocene is added as a combustion catalyst to increase the oxygen index of the plugging matrix to 45%, and the edge of the plugging matrix is ​​reinforced with a 2.5D braided structure with a braiding angle of 60° and a braiding density of 20×20 strands / cm 2 .

[0022] Furthermore, the edge of the elastic sealing layer is designed to have a stepped thickness gradient structure, which is divided into three steps from the center to the edge, forming a three-level sealing structure on the contact surface between the plugging cover and the nozzle; an annular groove with a width of 0.5mm and a depth of 0.2mm is processed on the outer edge of the sealing layer, and the groove is filled with fluorosilicone rubber to form a lip-shaped sealing structure. When the plugging cover is subjected to positive pressure, the lip-shaped sealing structure expands outward to enhance the sealing effect; when the plugging cover is subjected to reverse pressure, the stepped structure forms a decompression zone to reduce the stress on the sealing layer.

[0023] Furthermore, a spiral groove with a width of 0.4mm and a depth of 0.3mm is opened on the surface of the plugging cover base. The starting point of the groove is located at the center of the plugging cover and the end point is located at the edge. The spiral angle is 45° and the pitch is 5mm. Silicone rubber sealing material is filled in the groove to form a secondary sealing structure; a microhole with a diameter of 0.2mm is processed every 10mm at the bottom of the groove, and the microhole runs through the plugging cover base. When the elastic sealing layer fails, the leaked medium enters the maze groove through the microhole, extending the leakage path and improving the sealing reliability; a polyimide film with a thickness of 0.1mm is arranged between the plugging cover base and the elastic sealing layer, and air holes with a diameter of 0.1mm are evenly distributed on the film, and the spacing between the air holes is 2mm, so that the plugging cover can balance the internal and external pressures when the temperature changes drastically.

[0024] Compared with the existing technology, the beneficial effects of the present invention are:

[0025] The use of T1000 carbon fiber reinforced boron modified phenolic resin, combined with the [0° / ±45° / 90°] 4S ply design, makes the plugging base tensile strength reach 225MPa and the thermal expansion coefficient is reduced to 1.8×10 -6 / °C, with an ablation rate of 0.028mm / s, and maintaining structural integrity even under 3000°C gas erosion. The elastic sealing layer, modified by the introduction of graphene and polytetrafluoroethylene, increases tensile strength to 26.5MPa, reduces the friction coefficient to 0.11, and achieves a compression set rate of 12%. It achieves reliable sealing within the temperature range of -60°C to +200°C, solving the problem of traditional materials becoming brittle at low temperatures and softening at high temperatures.

[0026] Precision molding and gradient bonding technology breaks through the bottleneck of bidirectional pressure bearing. The segmented mold is combined with the micro-groove exhaust design, and the dimensional accuracy is controlled within ±0.03mm; the modified epoxy resin transition layer is combined with plasma surface treatment, and the interface shear strength reaches 30.5MPa, ensuring that the plug cap has a leakage rate of 10MPa in the forward direction and 6MPa in the reverse direction. The double-helix gluing process and laser positioning technology achieve uniformity control of the glue layer thickness to ±0.02mm, the coaxiality error between the plug and the nozzle is less than 0.06mm, and the axial tensile strength reaches 20.5MPa, effectively resisting launch vibration loads.

[0027] Post-processing enhancement and intelligent detection system ensure long-term reliability. High and low temperature cycle combined with supercritical extraction treatment; acoustic emission detection and helium mass spectrometry leak detection technology achieve 0.4mm 2 Micro-defect identification, acoustic emission signal count in water pressure test is less than 75 times / minute, ensuring aerospace-grade safety redundancy. A certain model verification test shows that the plugging cover of this application has been tested for 10 5 The performance degradation after one cycle is less than 2%, and the service life is up to 15 years, which is improved compared with traditional products. It provides a highly reliable sealing solution for heavy-lift launch vehicles and deep space exploration missions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the precision molding and high-strength bonding method for the bidirectional pressure-bearing plugging cover of a rocket nozzle proposed in the present invention;

[0029] Figure 2 The comparison of strength values ​​and strength improvement ratio between traditional epoxy resin and gradient transition layer of this method at different test temperatures;

[0030] Figure 3 The figure shows the defect rate comparison and improvement range of the traditional mold and the mold of the present invention under different defect types. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0033] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The present invention will be further described in detail below with reference to the accompanying drawings.

[0034] Reference Figures 1 to 3 A method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle comprises the following steps:

[0035] The following steps are used to form the capping matrix: High-strength carbon fibers are impregnated with a modified phenolic resin containing 5% boron. Unidirectional prepreg is prepared via a hot-melt method, with a resin content of 35% ± 1% and a volatile content of ≤ 0.8%. The gel time is stabilized at 120 ± 10 seconds at 170°C. An AFP-600 automatic fiber placement machine is used to implement a [0° / ±45° / 90°] 4S symmetrical cyclic layup process. A total of 32 layers are laid, with a single layer thickness of 0.125mm. The layup area is a φ200mm circular surface. A visual positioning system is used to control the fiber orientation deviation between adjacent layers to ≤ 0.8°, with inter-layer positioning accuracy of ±0.08mm. The layup environment is controlled at a temperature of 23 ± 2°C and a humidity of ≤ 40% RH.

[0036] The laminated blank is loaded into a quenched and tempered Cr12MoV heat-resistant steel mold, and the mold surface is precision-ground to an accuracy of ±0.025mm and a surface roughness of Ra≤0.15μm. A three-stage hot pressing process is used: first, the temperature is raised to 190°C at a rate of 3°C / min, and a uniform pressure of 4MPa is applied simultaneously. The 5 sets of K-type thermocouples embedded in the mold are used for real-time monitoring to ensure that the temperature difference of the mold surface is ≤3°C, and the pressure is maintained and cured for 2.5 hours. After curing, the temperature is lowered to below 50°C at a rate of 1°C / min to be demoulded. A five-axis CNC machining center is used for precision milling, and the outer diameter is controlled to φ200±0.03mm and the thickness is 9.8±0.03mm. The flatness is detected by a laser interferometer to be ≤0.025mm. The surface roughness is ground step by step with sandpaper to Ra≤0.6μm. The final molded matrix is ​​tested by ultrasonic C scanning to detect the internal porosity of ≤0.5%;

[0037] Preparation of the elastic sealing layer: A mixture of hydrogenated nitrile rubber (HNBR) with a 45% acrylonitrile content and 5μm polytetrafluoroethylene (PTFE) powder (7:3 by mass) was used. Graphene nanosheets were added to enhance thermal conductivity and wear resistance, while nanosilica enhanced interfacial sealing stability. 1% DCP was added as a vulcanizing agent. A twin-screw extruder with a 40:1 aspect ratio and a 50mm screw diameter was used. Nitrogen was used to protect the rubber from oxidation. Zones 1 (120°C), 2 (135°C), and 3 (155°C) were set, and the screw speed was 200 rpm for 15 minutes. After mixing, the extruder was rolled onto a three-roll calender into a 1.0mm thick, 220mm wide sheet with a thickness tolerance of ±0.02mm. The rolled sheet is cut into 210mm diameter circular blanks, placed in a Cr12MoV mold with venting grooves, and vulcanized on a flatbed vulcanizer at 170°C and 10MPa for 15 minutes. After vulcanization, it is trimmed using a five-axis laser cutting machine to a controlled outer diameter of 205±0.05mm, a thickness of 1.0±0.02mm, and a Shore A hardness of 75±3. Finally, the sealing layer undergoes plasma surface activation to improve adhesion to the transition layer. Its microroughness Ra is ≤0.4μm (AFM measurement), its loss factor is ≤0.15 from -60°C to 200°C, and its compression set is ≤10%, providing a stable and elastic sealing foundation for compression molding.

[0038] The transition layer treatment process involves placing the formed capping substrate in a vacuum chamber of an RF plasma treatment system. The chamber is pre-evacuated to 5 Pa (5 Pa), then purged with argon at a steady flow rate of 50 sccm. A 13.56 MHz RF power supply is activated to ignite the plasma at 120 W for 8 minutes. During the treatment, the chamber temperature is maintained at 60 ± 5°C. Ion bombardment and free radical reactions remove surface contaminants and etch the microstructure.

[0039] Gradient coating modification was then performed, with three solutions of different concentrations being prepared: the base layer consisted of a dilute solution containing 3% silane coupling agent KH-550, sprayed at a pressure of 0.3 MPa, a spray distance of 150 mm, a coating thickness of 0.1 mm, and dried at room temperature for 30 minutes; the surface layer consisted of a concentrated solution containing 10% silane coupling agent KH-550, blade-coated at a 45° blade angle, a pressure of 0.1 MPa, a coating thickness of 0.1 mm, and dried at room temperature for 2 hours; and the middle layer consisted of a standard solution containing 6% silane coupling agent KH-550, roller-coated at a speed of 60 rpm, a pressure of 0.2 MPa, a coating thickness of 0.15 mm, and dried at room temperature for 1 hour. The gradient coating process, by increasing the coupling agent solution from dilute to concentrated, forms a composite structure of "anchor layer-transition layer-bonding layer" on the substrate surface. This not only avoids the uneven coating caused by the high viscosity of high-concentration adhesives, but also enhances interfacial bonding strength through layer-by-layer stacking.

[0040] Molding composite molding steps: The mold design and manufacturing adopts a three-stage structure, consisting of an inner core mold, a middle mold sleeve and an outer mold sleeve. Different materials are selected for each layer of the mold according to functional requirements: the inner core mold directly contacts the molding material and is made of H13 hot working mold steel, which has a high temperature strength of 1200MPa and a thermal conductivity of 1000MPa. The hardness is controlled at HRC50-52 to withstand the forming pressure. The middle mold sleeve serves as a stress buffer and is made of 4Cr5MoSiV1 steel with a hardness of HRC48-50. The outer mold sleeve provides overall structural support and is made of 45 steel with a hardness of HB220-250, balancing strength and processing cost. The three-layer mold is assembled through a shrink-fit process: the outer mold sleeve is heated to 200°C, the inner core mold is cooled to -196°C with liquid nitrogen, and then quickly assembled and naturally cooled to form an interference fit of 0.05-0.1mm, ensuring a seamless mold fit even at high temperatures.

[0041] The mold surface is machined using a five-axis CNC grinder, achieving a final tolerance of ±0.02mm. The surface is then polished to Ra ≤ 0.15μm using diamond paste. To optimize resin flow and heat conduction, a honeycomb microgroove array is machined into the mold surface. Nanosecond laser etching is used to create rectangular microgrooves with a depth of 0.03±0.005mm and a width of 0.05±0.003mm, with a spacing of 1mm. The mold heating system consists of 24 φ12mm×200mm electric heating rods: eight in the inner core mold, 12 in the middle mold sleeve, and four in the outer mold sleeve. K-type thermocouples are used to measure temperature at five radially spaced points along the mold. PID temperature control is implemented using a Siemens S7-1200 PLC to ensure a temperature difference of ≤3°C between the substrate and the sealing layer.

[0042] During composite molding, the surface plasma-activated substrate, the transition layer-coated middle piece, and the plasma-treated elastic sealing layer are placed into the mold in sequence, precisely positioned by guide columns, and after the mold is closed, a 200-ton four-column hydraulic press applies a uniform pressure of 2MPa. The heating stage adopts dual-circuit control: the power of the heating rod in the substrate area is output at 90%, and the power of the heating rod in the sealing layer area is output at 70%. The temperature-time curve is monitored and the target temperature is raised and stabilized within 30 minutes. During the 45-minute pressure holding process, excess resin is discharged to the overflow trough of the mold through the microgroove array. At the same time, the microgrooves increase the contact area between the mold and the material, thereby improving the heat conduction efficiency. After molding, the mold water cooling system is started to cooperate with the electric heating rod for intermittent heating, and the temperature is cooled synchronously at a rate of 0.5℃ / min. When the mold temperature drops to 60℃, the mold is slowly demolded through the pneumatic ejection device to avoid interface stress concentration caused by temperature gradient.

[0043] The nozzle mounting surface is first sandblasted with 80-mesh white corundum grit at a blasting pressure of 0.4 MPa to a rough surface of Ra = 6.3 μm. Electroless nickel-phosphorus alloy plating is then performed using a solution consisting of 25 g / L nickel sulfate, 30 g / L sodium hypophosphite, 15 g / L sodium acetate, and 25 g / L lactic acid. Plating is performed at a pH of 4.5-5.0 and 85-90°C for 60 minutes, resulting in a 15 μm thick coating with a 10% phosphorus content. Heat treatment at 400°C for one hour enhances the coating's hardness and adhesion. The adhesive is prepared by mixing 100 parts phenol-formaldehyde resin, 20 parts nitrile rubber, 5 parts resorcinol, and 3% nano-alumina in a reaction vessel, heating to 120°C with stirring for 2 hours, and cooling to obtain the adhesive. The adhesive is applied using a double-spindle coating process, maintaining a thickness of 0.18 mm and a uniformity deviation of ≤±0.02 mm. During the assembly stage, the plugging cap is precisely aligned with the nozzle mounting surface through a laser positioning system with an accuracy of ±0.05mm, a pressure of 0.6MPa is applied to evenly distribute the adhesive, and vacuum-assisted exhaust technology is used to expel bubbles from the bonding layer. The device is then placed in an oven and heated to 150°C at a rate of 1°C / min and cured for 4.5 hours to ensure high-strength bonding between the plugging cap and the nozzle mounting surface, providing a reliable connection basis for the bidirectional pressure-bearing seal of the rocket nozzle.

[0044] Post-treatment and hardening steps: The assembled plugs undergo multiple stages of post-treatment and hardening, beginning with high-temperature cycling. They are mounted in a high-temperature and low-temperature test chamber equipped with a liquid nitrogen spray cooling system and infrared radiation heating, with a temperature uniformity of ≤±2°C. The cycle involves rapid cooling at a rate of 10°C / s to -60°C and holding for 2.5 hours. The infrared heating is then switched to heating at a rate of 8°C / s to +130°C and holding for 2.5 hours. After each cycle, the plugs are left at room temperature for one hour, with a contact thermometer measuring the surface and interior temperature difference to ≤5°C to ensure temperature uniformity. Following the high-temperature and low-temperature cycling, the plugs undergo a damp heat aging treatment. The plugs are placed in a double-walled damp heat test chamber, using a saturated steam generator to control humidity and an axial flow fan to maintain air circulation, maintaining a temperature of 75°C ±0.5°C. The samples remain in this environment for 56 hours. After the test, the plugs are removed and dried in a 60°C drying oven for 24 hours to ensure that no condensation remains on the surface.

[0045] Then, supercritical carbon dioxide extraction treatment is carried out: the plug is placed in a supercritical extraction reactor made of 316L stainless steel and maintained at a pressure of 20MPa and a temperature of 40°C for 2 hours. After the extraction is completed, the pressure is slowly reduced to normal pressure through the back pressure valve at a rate of 0.5MPa / min to avoid microcracks inside the material due to a sudden drop in pressure. Finally, radiation irradiation treatment is carried out: the plug is placed in a cobalt-60 irradiation device with a lead shielding layer thickness of 100mm and receives a total dose of 50kGy at a dose rate of 1kGy / h. Microwave annealing is carried out immediately after irradiation: the plug is placed on the rotating platform of a 2.45GHz microwave device and heated at a power of 500W for 10 minutes to promote molecular chain recombination and eliminate free radicals generated by irradiation. Key parameters such as temperature, pressure, and humidity are recorded by a data acquisition system at each treatment stage to ensure process consistency.

[0046] Performance testing steps: During the performance test, AGFAD4 type 400 sensitivity flaw detection film is used with X-ray flaw detector to perform X-ray flaw detection on the cover. The darkroom process strictly controls the development and fixing process. The brightness is ≥3000cd / m 2 , the film viewing light with a contrast ratio of ≥30:1 was used to interpret the film, and internal defects such as pores and cracks ≥0.1mm were detected, and the detection rate of interface debonding defects was ≥99%, ensuring the integrity of the bonding between the substrate and the sealing layer; then a water pressure test was carried out, using a high-precision water pressure test bench with a pressure control accuracy of ±0.01MPa, and deionized water with a conductivity of ≤5μS / cm as the medium. The pressure was increased at a rate of 0.5MPa / min through the servo hydraulic system, and the pressure was maintained for 30 minutes under the conditions of 10MPa in the forward direction and 6MPa in the reverse direction. During this period, the strain gauges evenly arranged around the edge of the plug monitored the strain value in real time to verify the bidirectional pressure bearing capacity; the PACMicro-30 acoustic emission system was used for monitoring simultaneously, and 4 sensors with a sensitivity of -65dB and a bandwidth of 20-1000kHz were evenly fixed on the plug surface through coupling agents to collect stress signals in real time; during stress assessment, the pressure value F(t) was collected in real time by a pressure sensor with an accuracy of ±0.01MPa, combined with the accurately measured 0.0314m 2 The load area A is calculated, and the coefficient λ=0.95 based on the material elastic modulus 294GPa is introduced. Calculate real-time stress. S is the actual stress on the plug, F(t) is the pressure value changing with time, A is the stress area of ​​the plug, and λ is the material stress correction factor. Ensure that the stress distribution at each pressure stage meets the design requirements. The final leakage rate is <5×10 −10 mbar·L / s.

[0047] In the present invention, the elastic sealing layer specifically incorporates 3% by mass of carbon nanotubes into the material formulation. This selection is based on the fact that the high aspect ratio of the carbon nanotubes allows them to form a three-dimensional thermally conductive network, and their 20nm diameter allows them to effectively embed themselves into the molecular gaps between hydrogenated nitrile rubber and polytetrafluoroethylene. To ensure uniform dispersion, the carbon nanotubes are first subjected to an acidification pretreatment and then proportionally added to the main ingredients, such as HNBR and PTFE, in a high-speed shear disperser. The disperser utilizes a double-end mechanical seal, with a set speed of 10,000 rpm and a dispersion time of 20 minutes. During the dispersion process, circulating cooling water is used to maintain the chamber temperature at ≤60°C. Scanning electron microscopy reveals that the carbon nanotubes are dispersed individually within the rubber compound, with no apparent agglomeration.

[0048] The addition of carbon nanotubes increased the thermal conductivity of the elastic sealing layer from 0.4W / (m・K) to 0.8W / (m・K), effectively reducing localized high temperatures in the sealing layer caused by frictional heat generation. The 200°C compression set was reduced from 22% to less than 15%, ensuring elastic recovery at high temperatures. In media immersion testing, samples were immersed in three rocket propellants: RP-1 kerosene, unsymmetrical dimethylhydrazine, and nitrogen tetroxide. After immersion, the mass change was measured using an electronic balance, and the volume change rate was controlled within ±3%. This significantly improves the sealing layer's adaptability to complex media environments and meets the sealing reliability requirements for long-term service in rocket nozzles.

[0049] In the present invention, the transition layer treatment step introduces an innovative formula related to shear strength and number of cycles: Where S is the shear strength after N cycles, is the initial shear strength, where ≥20MPa; k is the strength attenuation coefficient, determined according to the material properties; N is the number of cycles. This formula is used to evaluate the shear strength changes of the transition layer under different numbers of cycles, reflecting its fatigue resistance. Under low temperature conditions, the transition layer 5 The strength retention rate after the first cycle is ≥90%, meeting the fatigue resistance requirements.

[0050] In the present invention, in the performance testing step, ultrasonic C-scan technology uses a 10MHz high-frequency probe to perform full-size point-by-point testing of the plug at a scanning speed of 50mm / s. The water pressure test adopts a step-by-step loading strategy. After loading 1MPa at each level, the pressure is maintained for 10 minutes. During this period, fiber grating sensors are arranged at 10mm intervals along the circumferential and radial directions on the surface of the plug to monitor the strain distribution in real time. When the pressure reaches the design value, the maximum strain of the plug is ≤0.3%. During laser holographic interference detection, the He-Ne laser is divided into reference light and object light. The object light is expanded and irradiates the plug. The reflected light and the reference light form interference fringes on the holographic dry plate. The fringe spacing is analyzed through digital image processing, and the deformation of each area is calculated to ensure that the deformation uniformity deviation of the plug is ≤±5%. The combination of multi-dimensional detection technology, from internal defects, strain response to macroscopic deformation, provides comprehensive verification, providing quantitative data support for the bidirectional pressure bearing and sealing performance of the plug. Each link strictly adheres to aerospace-grade detection standards to ensure the reliability of the product in extreme environments.

[0051] In the present invention, the carbon fiber prepreg of the plugging substrate is formed by a vacuum-assisted autoclave process to precisely control the carbon fiber volume fraction at 65% ± 1%. The resin system uses a modified phenolic resin containing 5% boron to improve high temperature resistance through molecular design, and 2% ferrocene is added as a combustion catalyst. The edge of the substrate is reinforced with a 2.5D braided structure and is braided by a five-axis braiding machine with a braiding angle of 60° and 20×20 strands / cm. 2 The density forms a three-dimensional interwoven network. This structure increases the tensile strength of the edge area and improves the resistance to crack propagation through fracture toughness, effectively preventing cracking caused by edge stress concentration and meeting the structural reliability requirements of the rocket nozzle under extreme working conditions.

[0052] In the present invention, the edge of the elastic sealing layer adopts a precisely designed stepped thickness gradient structure, machined and formed using a five-axis CNC milling machine. From center to edge, it is divided into three steps: the first step is 10mm wide and 1.0mm thick, the second step is 8mm wide and 0.7mm thick, and the final step is 5mm wide and 0.3mm thick. Each step transition surface is manually polished with 320-grit sandpaper, creating a three-level gradient sealing area at the interface between the plug and the nozzle. Laser micromachining technology is used to form an annular groove with a width of 0.5±0.02mm and a depth of 0.2±0.01mm on the outer edge of the sealing layer. The groove is filled with a customized fluorosilicone rubber and hot-pressed and vulcanized to form a tightly fitting lip-shaped sealing structure. When the plug is subjected to positive pressure, the lip-shaped structure expands outward due to the fluid pressure, forming a dynamic clamping force with the contact surface of the nozzle. When subjected to reverse pressure, the three-stage stepped structure gradually attenuates the pressure load, forming a multi-stage pressure relief zone inside the sealing layer. Through finite element analysis, it is verified that the edge stress concentration coefficient is reduced and the reverse sealing performance is improved compared with a single structure. This design effectively takes into account the sealing reliability and structural durability under bidirectional pressure conditions.

[0053] In the present invention, a spiral groove is machined on the surface of the plugging cover substrate by a five-axis CNC engraving machine. The groove has a width of 0.4±0.03mm, a depth of 0.3±0.02mm, a helix angle of 45°, a pitch of 5mm, a starting point at the center of the substrate, and an end point extending to the edge, forming a continuous maze-like path. After the groove is roughened by laser pretreatment, it is filled with silicone rubber with a Shore hardness of A65. The bonding strength between the silicone rubber and the groove is ≥3MPa, forming a secondary sealing barrier. Micropores with a diameter of 0.2±0.01mm are punched at the bottom of the groove by ultraviolet laser. The micropores are arranged every 10mm along the direction of the groove and penetrate the thickness of the substrate. When the elastic sealing layer fails, the leaking medium needs to enter the groove through the micropores, and the path is extended to more than 3 times the original straight path.

[0054] A 0.1mm thick polyimide film is embedded between the substrate and the elastic sealing layer. The film is opened with air holes of 0.1±0.005mm in diameter through micromachining technology, and the hole spacing is 2mm. This ensures that when the temperature changes drastically, the internal and external gases are slowly exchanged through the air holes, balancing the pressure difference to ≤0.1MPa, thus avoiding damage to the sealing layer caused by excessive internal and external pressure difference. The composite structure has been verified by thermal cycle tests, and the leakage rate is always , fully guaranteeing the sealing reliability under extreme working conditions.

[0055] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle, characterized in that: The following steps are involved: S1: Plug base molding step: Use T1000 grade carbon fiber reinforced boron modified phenolic resin prepreg, the ply angle is designed according to the [0° / ±45° / 90°] 4S cycle symmetry, and cure it at 190℃ and 4MPa pressure for 2.5 hours through isothermal hot pressing process to form a 220MPa tensile strength and thermal expansion coefficient ≤2×10 -6 / ℃ plugging substrate; S2: Preparation of elastic sealing layer: Hydrogenated nitrile rubber and polytetrafluoroethylene powder were mixed in a mass ratio of 7:3, 2% graphene nanosheets, 0.5% nanosilica, and 1% vulcanizing agent DCP were added, and the mixture was kneaded at 155°C for 15 minutes using a twin-screw extruder, and then calendered into a 1.0 mm thick elastic sealing layer. S3: transition layer treatment step: plasma treatment is performed on the surface of the blocking substrate to form a micro-rough surface with Ra = 4.5 μm; Apply modified epoxy resin transition layer, cure at 120℃ for 1.5 hours, the shear strength between the transition layer and the substrate is 28MPa; S4: Compression molding step: Place the plugging and capping substrate, transition layer, and elastic sealing layer into the mold in sequence, maintain the pressure at 2 MPa for 45 minutes, and create microchannels with a width of 0.08 mm and a depth of 0.04 mm on the mold surface to ensure gas discharge during the molding process; S5: Plug cap assembly and bonding steps: Apply modified phenolic resin adhesive to the nozzle mounting surface using a spiral coating process. Use laser positioning technology to ensure that the coaxial error between the plug cap and the nozzle is less than 0.08mm. Curing at 150°C and 0.6MPa pressure for 4.5 hours. The axial tensile strength of the plug cap and nozzle is 18MPa. S6: Post-processing strengthening step: the formed plugging cover is subjected to high and low temperature cycle treatment, followed by wet heat aging treatment and radiation irradiation treatment; S7: Performance testing steps: X-ray inspection and water pressure test are performed on the plug cover. Acoustic emission detection technology is used to monitor stress changes. The stress-time evaluation formula is introduced: , S is the actual stress borne by the plugging cover, F(t) is the pressure value, A is the stress-bearing area of ​​the plugging cover, and λ is the correction coefficient.

2. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: The elastic sealing layer is further added with 3% by mass of carbon nanotubes, which are evenly dispersed using a shear disperser. This increases the thermal conductivity of the elastic sealing layer to 0.8W / (m·K), reduces the compression set at 200°C to ≤15%, and controls the volume change rate under medium immersion to within ±3%.

3. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: The transition layer modified epoxy resin contains 8% by mass of a core-shell structure toughening agent, with the core being butadiene rubber and the shell being methyl methacrylate. A gradient coating process is employed: the bottom layer is coated with a dilute solution containing 3% silane coupling agent and 40% solid content; the middle layer is coated with a standard solution containing 6% silane coupling agent and 60% solid content; and the surface layer is coated with a concentrated solution containing 10% silane coupling agent and 80% solid content. An innovative formula correlating shear strength with cycle count is introduced: , where S is the shear strength after N cycles, is the initial shear strength; k is the strength attenuation coefficient, which is determined according to the material properties; N is the number of cycles.

4. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: In the compression molding step, the mold adopts a segmented structural design and consists of an inner core mold, a middle mold sleeve and an outer mold sleeve. The inner core mold is made of H13 hot working die steel, the middle mold sleeve is made of 4Cr5MoSiV1 steel, and the outer mold sleeve is made of 45 steel. An interference fit is adopted between the three layers of the mold, and a micro-groove array with a depth of 0.03 mm and a width of 0.05 mm is processed on the mold surface. The micro-grooves are spaced 1 mm apart and distributed in a honeycomb shape, so that excess resin can be discharged through the micro-grooves during the molding process.

5. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: In the plugging cover assembly and bonding steps, the nozzle mounting surface is sandblasted before the adhesive is applied to form a rough surface with Ra=6.3μm, and then chemically plated with nickel-phosphorus alloy. After plating, it is heat treated at 400°C for 1 hour to increase the bonding strength between the adhesive and the nozzle to 20MPa; a double-helix coating process is adopted, and the coating thickness uniformity deviation is ≤±0.02mm; vacuum-assisted exhaust technology is used during the assembly process to form a negative pressure environment of -0.08MPa between the nozzle and the plugging cover to expel bubbles in the adhesive layer, so that the porosity of the adhesive layer is less than 1%.

6. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: In the post-treatment strengthening step, high and low temperature cycle treatment adopts a combination of liquid nitrogen spray cooling and infrared radiation heating to generate controllable micro-stress inside the plugging cover; supercritical carbon dioxide extraction treatment is performed after wet heat aging treatment to remove small molecular substances remaining inside the plugging cover; microwave annealing treatment is performed after radiation treatment to eliminate free radicals generated by radiation and restore material properties.

7. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: In the performance testing step, ultrasonic C-scan detection technology is used to perform a full-size scan of the interior of the plugging cover; the water pressure test adopts a step-by-step loading method, and the strain distribution of the plugging cover is simultaneously monitored. When the pressure reaches the design value, the maximum strain of the plugging cover is ≤0.3%; laser holographic interferometry technology is used to detect the deformation of the plugging cover under pressure.

8. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: The carbon fiber prepreg of the plugging substrate has a carbon fiber volume fraction controlled at 65% ± 1%. The resin system uses boron-modified phenolic resin and adds 2% ferrocene as a combustion catalyst to increase the oxygen index of the plugging substrate to 45%. The edge of the plugging substrate is reinforced with a 2.5D braided structure with a braid angle of 60° and a braid density of 20×20 strands / cm. 2 .

9. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: The edge of the elastic sealing layer is designed to have a stepped thickness gradient structure, which is divided into three steps from the center to the edge, forming a three-level sealing structure on the contact surface between the plugging cover and the nozzle; an annular groove with a width of 0.5mm and a depth of 0.2mm is processed on the outer edge of the sealing layer, and the groove is filled with fluorosilicone rubber to form a lip-shaped sealing structure. When the plugging cover is subjected to positive pressure, the lip-shaped sealing structure expands outward to enhance the sealing effect. When the plugging cover is subjected to reverse pressure, the stepped structure forms a decompression zone to reduce the stress on the sealing layer.

10. The method for precision molding and high-strength bonding of a bidirectional pressure-bearing plugging cover for a rocket nozzle according to claim 1, characterized in that: A spiral groove with a width of 0.4 mm and a depth of 0.3 mm is provided on the surface of the plugging cover base. The groove starts at the center of the plugging cover and ends at the edge. The spiral angle is 45° and the pitch is 5 mm. The groove is filled with silicone rubber sealing material to form a secondary sealing structure. A microhole with a diameter of 0.2mm is processed every 10mm at the bottom of the groove. The microhole penetrates the plugging cover substrate. When the elastic sealing layer fails, the leaking medium enters the labyrinth groove through the microhole, extending the leakage path and improving the sealing reliability. A polyimide film with a thickness of 0.1mm is set between the plugging cover substrate and the elastic sealing layer. Air holes with a diameter of 0.1mm are evenly distributed on the film, and the spacing between the air holes is 2mm, so that the plugging cover can balance the internal and external pressures when the temperature changes drastically.

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