A method of forming a composite flexible joint

Abstract

This invention discloses a method for molding a flexible joint made of composite materials, including a movable inverted cone, a reinforcement, and a fixed joint; a pre-formed rubber elastic sheet is prepared; the movable inverted cone, the reinforcement, and the fixed joint are placed in a mold for trial molding; after trial molding, the movable inverted cone, the reinforcement, and the fixed joint are placed in an integrated thermoforming mold for simulated vulcanization, and the parameters of the simulated vulcanization are consistent with those of the actual vulcanization; after the simulated vulcanization is completed, the parallelism, height h, and thickness t are measured. i The total rubber overflow C is measured and pretreated after meeting the requirements; finally, it is placed in an integrated molding mold for compression molding. The pre-cured rubber elastic layer can better ensure the uniformity of the rubber elastic layer thickness, thereby improving the parallelism, height and swing performance of the flexible joint; the use of all-composite material flexible joints can greatly reduce the self-weight, reduce the negative mass of the nozzle, and at the same time shorten the production cycle of the flexible joint, improve material utilization and improve product performance.

Description

Technical Field

[0001] This invention relates to the field of flexible joint molding technology, and more specifically to a method for molding a flexible joint made of composite materials. Background Technology

[0002] The working principle of a solid rocket motor is to convert the thermal energy of the propellant combustion gas generated in the combustion chamber into the kinetic energy of the gas flow through the energy conversion device—the nozzle—thereby obtaining the desired thrust. The flexible joint in the flexible oscillating nozzle not only needs to withstand the axial thrust generated during the thrust formation process, but also moves circumferentially along the oscillation center under the action of the servo control system, affecting the engine's attitude and trajectory control processes. Therefore, the pressure-bearing and oscillation performance of the flexible joint is a crucial factor affecting the operating state of the flexible oscillating nozzle.

[0003] The flexible joint is a crucial component of the oscillating nozzle. It not only withstands the axial thrust generated during thrust formation but also undergoes circumferential motion along the oscillating center under the control of the servo control system, affecting the engine's attitude and trajectory control. Therefore, the pressure-bearing and oscillation performance of the flexible joint are significant factors influencing the operating condition of the flexible oscillating nozzle. The flexible joint consists of front and rear flanges, reinforcements, and a rubber elastic layer. The strength, stiffness, and dimensional accuracy of the reinforcements affect the molding quality and mechanical properties of the flexible joint.

[0004] Currently, flexible joint reinforcement components are generally machined from low-alloy ultra-high strength steel 30CrMnSiA or 30Si2MnCrMoVe forged rings. Due to their thin-walled concentric spherical ring structure, the machining precision is high and the processing difficulty is significant. Each reinforcement component requires tooling for auxiliary machining and forming, but the scrap rate remains high, and the material utilization rate is very low. According to model and physical calculations, the material utilization rate of metal reinforcement components from forging to finished product is only 2%, and the larger the product size, the lower the material utilization rate. Moreover, more than 97% of the weight of the flexible joint comes from the metal components. The heavier the flexible joint, the greater the negative mass of the nozzle, which leads to a decrease in nozzle working efficiency. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned technical deficiencies by providing a method for molding flexible composite material joints that shortens the production cycle, improves material utilization, and reduces weight.

[0006] To achieve the above objectives, the present invention provides a method for molding a flexible joint of composite materials. The flexible joint includes a movable inverted cone, a reinforcing member, and a fixed joint. The specific molding method is as follows:

[0007] 1) Prepare pre-formed rubber elastic sheets and weigh and mark each rubber elastic sheet as A. i Let i represent the i-th elastic rubber sheet, where i is a natural number; and Ai =A 0i +(7-8%)A 0i A 0i This represents the theoretical weight of the i-th rubber elastic sheet;

[0008] 2) Place the movable inverted cone, reinforcement and fixed rear joint into the mold for trial molding. If the gap between the upper mold and the lower mold is ≤0.2mm after mold closing, the initial surface of the movable inverted cone, reinforcement and fixed rear joint is qualified in terms of shape and position. Proceed to step 3).

[0009] 3) Place the movable inverted cone, the reinforcing part, and the fixed rear joint into the integrated thermoforming mold, and place rubber elastic sheets between the movable inverted cone and the reinforcing part, between the reinforcing parts and the reinforcing part, and between the reinforcing part and the fixed rear joint. After the mold is closed, simulate vulcanization. The parameters of simulated vulcanization are consistent with the parameters of actual vulcanization.

[0010] 4) After the simulated vulcanization is completed, check the parallelism and dimensional position of the height h of the flexible joint, and measure the thickness t of each layer of rubber elastic sheet after vulcanization. i The uniformity of the rubber elastic sheet and the total rubber overflow C of the rubber elastic sheet are determined by weighing the vulcanized rubber elastic sheet to obtain the weight D of each layer of vulcanized rubber elastic sheet. i ;

[0011] If ΣD is satisfied i +C≈ΣA i 0.5mm≤t i If -t0≤0.5mm, parallelism≤0.3, and -0.5mm≤h≤0.5mm, then proceed to step 5), where t0 is the theoretical thickness of the rubber elastic sheet;

[0012] 5) Pre-treat the mating surfaces of the movable inverted cone, reinforcing parts, and fixed rear joint;

[0013] 6) The movable inverted cone, reinforcement, fixed joint and rubber elastic layer, which have been pretreated in step 5), are stacked in sequence and placed in an integrated molding mold for compression molding.

[0014] Furthermore, in step 2), if the gap between the upper mold and the lower mold is >0.2mm after mold closing, the movable inverted cone, the reinforcing member and / or the fixed rear connector are replaced until the shape and position dimensions are qualified.

[0015] Furthermore, in step 4), if the parallelism ≤ 0.3 and -0.5mm ≤ h ≤ 0.5mm are not satisfied, mold repair is performed; if 0.5mm ≤ t is not satisfied... i If -t0≤0.5mm, add or subtract material from each layer of rubber elastic sheet, adjusting by 1g each time.

[0016] Further, the specific pretreatment process in step 5) is as follows: the mating surfaces of the movable inverted cone, the reinforcing member, and the fixed rear joint are uniformly polished to roughen the mating surfaces. Then, the mating surfaces are cleaned with anhydrous ethanol and placed in an oven at 50±5℃ for 10-15 minutes to dry. Then, the adhesive is applied clockwise and unidirectionally to the mating surfaces of the movable inverted cone, the reinforcing member, and the fixed rear joint. After drying until it becomes stringy to the touch, a second coat is applied clockwise and unidirectionally to each mating surface. After drying, it is placed in an oven at 80±5℃ for 5-10 minutes to dry. The same operation is performed on one side of each layer of rubber elastic sheet. After drying, it is placed in an oven at 50±5℃ for 10-15 minutes to dry.

[0017] Furthermore, the specific process of compression molding in step 6 is as follows: the movable inverted cone, the reinforcing part, the fixed rear joint and the rubber elastic layer are stacked in sequence and placed in an integrated molding mold. After cold pressing at 1-2 MPa, the parts are vented 3-5 times to preliminarily shape and position each part.

[0018] Then, heat to 75±5℃, pressurize to 3~4MPa, and hold for 3~5 minutes, releasing pressure and venting 2~3 times during the holding period; continue heating to 90±5℃, pressurize to 4~6MPa, and hold for 5~8 minutes; continue heating to 120±5℃, pressurize to 6~7MPa, and hold for 5~8 minutes; continue heating to 150±5℃, pressurize to 7~9MPa, and hold for 30~40 minutes, then cool with the equipment to below 60℃, and then release the pressure and cool to room temperature before demolding.

[0019] Furthermore, the movable inverted cone, the reinforcing member, and the fixed rear joint are all three-dimensional woven carbon fiber + RTM composite molded parts, and the molding methods are the same, specifically:

[0020] 1) Mechanically weave 3K carbon fiber into an integral ring shape with a warp and weft needle pitch of 3mm×3mm~5mm×5mm. The normal thickness and part thickness meet the following requirements: 12.5%≤(t-t0) / t≤20%, where t is the thickness of the woven cover and t0 is the thickness of the part. Then, perform pre-compression molding on a pre-compression molding fixture. The cavity thickness requirement of the pre-compression molding fixture is: 7.5%≤(T-t0) / T≤10%, and the pre-compression time is 12~24h, where T is the pre-compression molding thickness of the woven cover. After pre-compression molding, perform non-destructive testing. After checking that there are no wrinkles on the inner and outer surfaces of the fabric, proceed to step 2).

[0021] 2) Place the pre-compressed braided body onto the male mold of the RTM molding die, close the female mold, and perform a tooling airtightness test; after passing the test, vacuum to -0.1 to -0.2 MPa for 2 to 4 hours to ensure that the RTM-molded product has no holes or cracks or low-density shadow areas with large CT values.

[0022] 3) Preheat the RTM molding die, phenolic resin, and adhesive injection equipment to 100℃~130℃. Then, slowly inject the adhesive using the adhesive injection equipment at a low pressure of 2~3MPa until the adhesive overflows from the outlet of the RTM molding die. Close the outlet and maintain the pressure for 0.5~1h. Then open the outlet and vent. Observe that no bubbles emerge from the outlet and close the outlet again. Finally, maintain the pressure and heat the RTM molding die to ensure that the resin fully impregnates the fiber.

[0023] The specific process of heating and curing is as follows: heat to 160°±5°C at a heating rate of 1°C / min and hold for 2.5 hours; then continue heating to 195°±5°C at a heating rate of 0.5°C / min and hold for 4 hours. Finally, cool with the furnace to 60°±5°C and remove.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention uses a pre-cured rubber elastic layer, which can better ensure the uniformity of the rubber elastic layer thickness, thereby improving the parallelism, height and swing performance of the flexible joint; using a full composite material flexible joint can greatly reduce its weight, reduce the negative mass of the nozzle, and at the same time shorten the production cycle of the flexible joint, improve material utilization and improve product performance.

[0026] This invention employs a single-layer three-dimensional braided body, which not only possesses the characteristics of lightweight, high strength, high modulus, high efficiency, and good quality consistency of composite materials, but also overcomes the problems of low interlaminar shear strength and quality instability caused by manual operation in laminated composite materials formed by lay-up or winding technology. The RTM molding process has the advantages of manufacturing high quality, high precision, low porosity, high fiber volume fraction, and good process design. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments to facilitate a clearer understanding of the present invention, but these embodiments do not constitute a limitation on the present invention.

[0028] The composite material flexible joint includes a movable inverted cone, a reinforcement, and a fixed joint. The specific molding method is as follows:

[0029] 1) Prepare pre-formed rubber elastic sheets and weigh and mark each rubber elastic sheet as A. i Let i represent the i-th elastic rubber sheet, where i is a natural number; and A i =A 0i +(7-8%)A 0i A 0i This represents the theoretical weight of the i-th rubber elastic sheet, ensuring that there are no gaps between layers during the subsequent vulcanization process, i.e., there needs to be a significant overflow of rubber during simulated vulcanization.

[0030] 2) Place the movable inverted cone, reinforcement and fixed rear connector into the mold for trial molding. If the gap between the upper mold and the lower mold is ≤0.2mm after mold closing, the initial surface of the movable inverted cone, reinforcement and fixed rear connector is qualified in terms of shape and position. Proceed to step 3). Otherwise, replace the unqualified movable inverted cone, reinforcement and / or fixed rear connector until the shape and position are qualified.

[0031] 3) Place the movable inverted cone, the reinforcing part, and the fixed rear joint into the integrated thermoforming mold, and place rubber elastic sheets between the movable inverted cone and the reinforcing part, between the reinforcing parts and the reinforcing part, and between the reinforcing part and the fixed rear joint. After the mold is closed, simulate vulcanization. The parameters of simulated vulcanization are consistent with the parameters of actual vulcanization.

[0032] 4) After the simulated vulcanization is completed, check the parallelism and dimensional position of the height h of the flexible joint, and measure the thickness t of each layer of rubber elastic sheet after vulcanization. i The uniformity of the rubber elastic sheet and the total rubber overflow C of the rubber elastic sheet are determined by weighing the vulcanized rubber elastic sheet to obtain the weight D of each layer of vulcanized rubber elastic sheet. i ;

[0033] If ΣD is satisfied i +C≈ΣA i 0.5mm≤t i If -t0≤0.5mm (t0 is the theoretical thickness of the rubber elastic sheet), parallelism≤0.3, and -0.5mm≤h≤0.5mm, then proceed to step 6); otherwise, proceed to step 7 (for straight lines).

[0034] 5) If the parallelism and height h are not within the range of step 5), then perform mold repair; if t i If -t0 is not within the range of step 5), then add or subtract material from each layer of rubber elastic sheet, adjusting by 1g each time; then repeat step 4).

[0035] 6) Evenly grind the mating surfaces of the movable inverted cone, reinforcement, and fixed rear joint to roughen the mating surfaces. Then clean the mating surfaces with anhydrous ethanol and dry them in an oven at 50±5℃ for 10-15 minutes. Next, apply adhesive clockwise and unidirectionally to the mating surfaces of the movable inverted cone, reinforcement, and fixed rear joint. After drying until the surface feels stringy to the touch, apply a second coat clockwise and unidirectionally to each mating surface. After drying, place it in an oven at 80±5℃ and dry for 5-10 minutes. Repeat the same operation to apply adhesive to one side of each layer of rubber elastic sheet. After drying, place it in an oven at 50±5℃ and dry for 10-15 minutes.

[0036] 7) Place the movable inverted cone, reinforcing parts, fixed rear joint and rubber elastic layer processed in step 6) into an integrated molding mold in an alternating manner. After cold pressing at 1-2 MPa, perform 3-5 venting cycles to preliminarily shape and position each component.

[0037] Then, heat to 75±5℃, pressurize to 3~4MPa, and hold for 3~5 minutes, releasing pressure and venting 2~3 times during the holding period; continue heating to 90±5℃, pressurize to 4~6MPa, and hold for 5~8 minutes; continue heating to 120±5℃, pressurize to 6~7MPa, and hold for 5~8 minutes; continue heating to 150±5℃, pressurize to 7~9MPa, and hold for 30~40 minutes, then cool with the equipment to below 60℃, and then release the pressure and cool to room temperature before demolding.

[0038] 8) Clean the excess adhesive from the surface of the all-composite flexible joint, and conduct a water pressure swing test and strength verification test on the flexible joint to verify that its mechanical properties meet the design requirements.

[0039] The movable inverted cone, the reinforcing component, and the fixed rear joint are all carbon fiber three-dimensional braided body + RTM composite molded parts. Since the molding methods are the same, the molding of the reinforcing component will be described in detail below, and the others will not be described in detail.

[0040] 1) 3K carbon fiber is mechanically woven into an integral ring shape with a warp and weft stitch pitch of 3mm×3mm~5mm×5mm. The normal thickness and part thickness meet the following requirements: 12.5%≤(t-t0) / t≤20%, where t is the thickness of the woven cover and t0 is the thickness of the part, to ensure sufficient compression ratio. Then, pre-compression molding is performed on a pre-compression molding fixture. The cavity thickness requirement of the pre-compression molding fixture is: 7.5%≤(T-t0) / T≤10%, and the pre-compression time is 12~24h, where T is the pre-compression molding thickness of the woven cover. After pre-compression molding, non-destructive testing (DR) is performed to check that there are no wrinkles on the inner and outer surfaces of the fabric before proceeding to step 2). The pre-compressed product is easier and more precise to place into the RTM molding fixture, further reducing the risk of surface wrinkles.

[0041] 2) Place the pre-compressed braided body onto the male mold of the RTM molding die, close the female mold, and perform a tooling airtightness test; after passing the test, vacuum to -0.1 to -0.2 MPa for 2 to 4 hours to ensure that the RTM-molded product has no holes or cracks or low-density shadow areas with large CT values.

[0042] 3) Preheat the RTM molding die, phenolic resin, and adhesive injection equipment to 100℃~130℃. Then, slowly inject the adhesive using the adhesive injection equipment at a low pressure of 2~3MPa until the adhesive overflows from the outlet of the RTM molding die. Close the outlet and maintain the pressure for 0.5~1h. Then open the outlet and vent. Observe that no bubbles emerge from the outlet and close the outlet again. Finally, maintain the pressure and heat the RTM molding die to ensure that the resin fully impregnates the fiber.

[0043] The specific process of heating and curing is as follows: heat to 160°±5°C at a heating rate of 1°C / min and hold for 2.5 hours; then continue heating to 195°±5°C at a heating rate of 0.5°C / min and hold for 4 hours. Finally, cool with the furnace to 60°±5°C and remove.

[0044] 5) Open the mold, remove the product using the ejector screws, clean up excess cured adhesive, and perform non-destructive testing (DR). If no holes, cracks, or low-density shadow areas are found, the product is acceptable for use.

[0045] The density of the carbon fiber braid is approximately 1.2 g / mm². -3 The weight of a single-layer three-dimensional braided composite material is approximately 0.15 times that of a metal part of the same volume. It not only possesses the advantages of lightweight, high strength, high modulus, and high efficiency and consistent quality of mechanical braiding found in composite materials, but also overcomes the problems of low interlaminar shear strength and quality instability caused by manual operation in laminated composite materials formed using layup or winding techniques. The RTM molding process offers advantages such as high quality, high precision, low porosity, high fiber volume fraction, and good process design flexibility. Therefore, the use of three-dimensional braided composite materials combined with RTM molding technology for movable inverted cones, reinforcements, and fixed rear joints shows promising development prospects.

[0046] In addition, the pre-cured rubber elastic layer can better ensure the uniformity of the rubber elastic layer thickness, thereby improving the parallelism, height and swing performance of the flexible joint; the use of all-composite flexible joints can greatly reduce the weight, reduce the negative mass of the nozzle, and at the same time shorten the production cycle of the flexible joint, improve material utilization and improve product performance.

Claims

1. A method for molding a flexible joint made of composite materials, the flexible joint comprising a movable inverted cone, a reinforcing member, and a fixed joint, characterized in that: The specific molding method is as follows: 1) Prepare pre-formed rubber elastic sheets and weigh and mark each rubber elastic sheet as A. i Let i represent the i-th elastic rubber sheet, where i is a natural number; and A i = A 0i + (7~8%)A 0i A 0i This represents the theoretical weight of the i-th rubber elastic sheet; 2) Place the movable inverted cone, reinforcing component, and fixed rear connector into the mold for trial molding. If the gap between the upper and lower molds is ≤0.2mm after mold closing, the initial surface dimensions of the movable inverted cone, reinforcing component, and fixed rear connector are qualified, and proceed to step 3). 3) Place the movable inverted cone, the reinforcing part, and the fixed rear joint into the integrated thermoforming mold, and place rubber elastic sheets between the movable inverted cone and the reinforcing part, between the reinforcing parts and the reinforcing part, and between the reinforcing part and the fixed rear joint. After the mold is closed, simulate vulcanization. The parameters of simulated vulcanization are consistent with the parameters of actual vulcanization. 4) After the simulated vulcanization is completed, check the parallelism and dimensional dimensions of the height h of the flexible joint, and measure the thickness t of each layer of rubber elastic sheet after vulcanization. i The uniformity of the rubber elastic sheet and the total rubber overflow C of the rubber elastic sheet are determined by weighing the vulcanized rubber elastic sheet to obtain the weight D of each layer of vulcanized rubber elastic sheet. i ; If ΣD is satisfied i +C≈ΣA i 0.5mm≤t i If -t0≤0.5mm, parallelism≤0.3, and -0.5mm≤h≤0.5mm, then proceed to step 5), where t0 is the theoretical thickness of the rubber elastic sheet; 5) Pre-treat the mating surfaces of the movable inverted cone, reinforcing parts, and fixed rear joint; 6) The pre-treated movable inverted cone, reinforcing member, fixed joint and rubber elastic layer are stacked in sequence and placed in an integrated molding mold for compression molding; The movable inverted cone, the reinforcing member, and the fixed rear joint are all carbon fiber three-dimensional braided body + RTM composite molded parts, and the molding methods are the same, specifically: 1) Mechanically weave 3K carbon fiber into a monolithic ring with a warp and weft stitch pitch of 3mm×3mm~5mm×5mm. The normal thickness and part thickness must meet the following requirements: 12.5%≤(t-t0) / t≤20%, where t is the thickness of the woven cover and t0 is the thickness of the part. Then, perform pre-compression molding on a pre-compression molding fixture. The cavity thickness requirement for the pre-compression molding fixture is: 7.5%≤(T-t0) / T≤10%, and the pre-compression time is 12~24h, where T is the pre-compression molding thickness of the woven cover. After pre-compression molding, perform non-destructive testing. After checking that there are no wrinkles on the inner and outer surfaces of the fabric, proceed to step 2). 2) Place the pre-compressed braided body onto the male mold of the RTM molding die, close the female mold, and perform a tooling airtightness test; after passing the test, vacuum to -0.1~-0.2MPa for 2~4 hours to ensure that the RTM-molded product has no holes or cracks or low-density shadow areas with large CT values. 3) Preheat the RTM molding die, phenolic resin, and adhesive injection equipment to 100°C ~ 130°C. Then, slowly inject the adhesive using the adhesive injection equipment at a low pressure of 2 ~ 3 MPa until the adhesive overflows from the outlet of the RTM molding die. Close the outlet and maintain the pressure for 0.5 ~ 1 hour. Then open the outlet and vent. Observe that no bubbles emerge from the outlet and close the outlet again. Finally, maintain the pressure and heat the RTM molding die to ensure that the resin fully impregnates the fiber. The specific process of heating and curing is as follows: heat to 160°±5°C at a heating rate of 1°C / min and hold for 2.5 hours; then continue heating to 195°±5°C at a heating rate of 0.5°C / min and hold for 4 hours; finally, cool with the furnace to 60°±5°C and remove.

2. The method for forming a flexible joint of composite materials according to claim 1, characterized in that: In step 2), if the gap between the upper and lower molds is >0.2mm after mold closing, replace the movable inverted cone, the reinforcing part and / or the fixed rear connector until the shape and position dimensions are qualified.

3. The method for forming a flexible joint of composite materials according to claim 1, characterized in that: In step 4), if the parallelism is not ≤0.3 and -0.5mm≤h≤0.5mm, then mold repair is performed; if 0.5mm≤t is not met... i If -t0≤0.5mm, add or subtract material from each layer of rubber elastic sheet, adjusting by 1g each time.

4. The method for forming a flexible joint of composite materials according to claim 1, characterized in that: The specific pretreatment process in step 5) is as follows: the mating surfaces of the movable inverted cone, the reinforcing part, and the fixed rear joint are uniformly polished to roughen the mating surfaces. Then, the mating surfaces are cleaned with anhydrous ethanol and placed in an oven at 50±5℃ for 10~15 minutes to dry. Then, the adhesive is applied clockwise and unidirectionally to the mating surfaces of the movable inverted cone, the reinforcing part, and the fixed rear joint. After drying until it is stringy to the touch, a second coat is applied clockwise and unidirectionally to each mating surface. After drying, it is placed in an oven at 80±5℃ and dried for 5~10 minutes. The same operation is performed to apply adhesive to one side of each layer of rubber elastic sheet. After drying, it is placed in an oven at 50±5℃ and dried for 10~15 minutes.

5. The method for forming a flexible joint of composite materials according to claim 1, characterized in that: The specific process of compression molding in step 6 is as follows: the movable inverted cone, the reinforcing part, the fixed rear joint and the rubber elastic layer are placed in an integrated molding mold in an alternating manner and then subjected to cold pressing at 1~2MPa for 3~5 times of venting to initially shape and position each component. Then, heat to 75±5℃, pressurize to 3~4MPa, and hold for 3~5 minutes, releasing pressure and venting 2~3 times during the holding period; continue heating to 90±5℃, pressurize to 4~6MPa, and hold for 5~8 minutes; continue heating to 120±5℃, pressurize to 6~7MPa, and hold for 5~8 minutes; continue heating to 150±5℃, pressurize to 7~9MPa, and hold for 30~40 minutes, then cool with the equipment to below 60℃, and then release the pressure and cool to room temperature before demolding.