Rocket engine composite case and connecting skirt integrated structure and forming method

Abstract

A rocket engine composite shell and connecting skirt integrated structure and forming method relates to a rocket engine shell structure and forming method. The shell is a hollow cavity made of composite fiber cloth winding, which is divided into an inner cylinder section in the middle part in a conical shape and a joint and a head integrally arranged at both ends in a spherical shell shape and reserved with a center hole. The test base is made of composite winding and integrally arranged at the joint end of the shell for subsequent axial test. The connecting skirt is made of composite winding and connected to the end of the head of the shell through the lap area to be integrated, including the connecting skirt section lapped on the inner cylinder section and the in-skirt layer uniformly laid between the connecting skirt section and the shell. In the forming process of the engine shell, the connecting skirt is formed, the shell and the connecting skirt are co-cured by composite material, the consistency of the shell and the connecting skirt is ensured, the structure and the process are simplified, and the reliability is higher.

Description

Technical Field

[0001] This invention relates to a rocket engine casing structure and molding method, and more particularly to an integrated structure and molding method for a rocket engine composite casing and connecting skirt, belonging to the field of engine casing manufacturing technology. Background Technology

[0002] Solid rocket engines are widely used in launch vehicles and missiles due to their simple structure, ease of storage, and safety and reliability. The casing is the primary site of fuel combustion, while the connecting skirt connects the casing to the cabin structure, transmitting thrust to the spacecraft. The structure must withstand not only the internal pressure and erosion from the high-temperature, high-pressure combustion gases, but also various loads such as axial compression and bending moments from the connected structures.

[0003] With increasing demands for flight speed, maneuverability, and payload, aircraft place higher requirements on engine casings and connecting skirts. Compared to traditional metal engine casings, fiber-reinforced composite materials offer superior design flexibility, improving not only the specific stiffness and specific strength of the engine casing but also providing excellent high-temperature resistance and corrosion resistance. However, the problem of low connection strength between the engine casing and connecting skirts remains unresolved.

[0004] The connection between the solid rocket motor casing and the connecting skirt must ensure continuous and coordinated deformation of the connection area during high-speed flight, preventing stress concentration and achieving a reliable seal. Traditional bolted, pinned, and keyed connections not only increase the weight of the aircraft structure, but also extend manufacturing time due to the manufacturing and machining processes of the connecting joints, as well as the assembly of parts such as seals and flanges. Furthermore, they often generate significant stress in the connection area, posing a significant challenge to the strength of the connecting parts and reducing structural reliability. The integrated molding technology of composite material casing and connecting skirt can fundamentally solve these problems, better ensuring the consistency and stability of the mechanical properties of the casing-connecting skirt connection area. Simultaneously, through advanced layup processes, based on the stress conditions of the connecting skirt during engine operation, and fully utilizing the designability of composite materials, reinforcing fibers or fiber fabrics can be laid at different locations such as the skirt ends and skirt tips according to the main load directions of each location, thereby improving the mechanical properties of the composite material connecting skirt. Therefore, the integrated molding technology of composite material casing and connecting skirt is a key focus in current engine casing research. Summary of the Invention

[0005] To overcome the problems of decreased interfacial shear strength and difficulty in controlling the assembly gap between the shell and the connecting skirt when using traditional connection methods for existing engine casings and connecting skirts, and to eliminate the machining process of the connecting skirt and reduce the assembly time of engine components, this invention provides an integrated structure and molding method for rocket engine composite casings and connecting skirts. It forms the connecting skirt during the engine casing molding process and co-cures the shell and connecting skirt with composite materials, ensuring the consistency between the shell and the connecting skirt, simplifying the structure and process, and improving reliability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An integrated structure of a rocket engine composite shell and connecting skirt includes a test base, a shell, and a connecting skirt. The shell is a hollow cavity made of composite fiber cloth wound together. The diameter difference between the two ends of the hollow cavity makes it conical in shape. It is divided into an inner cylinder section that is conical in the middle and a joint and a head that are integrally set at both ends of the inner cylinder section and have reserved central holes. The joint is set at the small diameter end of the inner cylinder section, and the head is set at the large diameter end of the inner cylinder section. The test base is made of composite material wound together and is integrally set at one end of the joint of the shell for subsequent axial compression test. The connecting skirt is made of composite material wound together and is connected to one end of the shell head through an overlap area. The overlap area includes a connecting skirt section that overlaps the inner cylinder section and a skirt inner layer that is uniformly laid between the connecting skirt section and the shell.

[0008] A method for molding an integrated structure of a rocket engine composite shell and connecting skirt includes the following steps:

[0009] Step 1: Wrapping the shell composite material

[0010] After the shell winding fixture is installed, the shell is wound circumferentially and longitudinally using resin-impregnated composite fiber cloth. During the longitudinal winding process, fibers are reserved at one end of the inner cylinder section corresponding to the end cap valve. When forming the connecting skirt section later, some of the reserved fibers are laid in the connecting skirt structure layer to form the skirt inner layer. During the circumferential winding process, the winding width is gradually increased to be the same as the width between the joint valve and the edge of the end cap valve of the shell winding fixture.

[0011] Step 2: Reinforce and wrap the connecting skirt mesh

[0012] After the connecting skirt winding fixture is installed, the connecting skirt is wound with a mesh reinforcement using composite materials. The longitudinal reinforcing fibers in the mesh reinforcement are taken from the remaining reserved fibers during the longitudinal winding process of the shell. The transverse reinforcing fibers in the mesh reinforcement are made of composite materials. The thickness of the longitudinal and transverse reinforcing fibers is ensured to be the same as the depth of the transverse and longitudinal grooves reserved on the outer wall of the segmented mold of the connecting skirt winding fixture. The layup angle of the mesh reinforcement composite material is based on the reinforcement direction.

[0013] Step 3: Connecting the skirt skin and wrapping it

[0014] The skin of the connecting skirt is wound, and the resin-impregnated composite material is wrapped around the outside of the mesh reinforcement of the connecting skirt from one end of the shell until it is flush with the step reserved at the end of the segmented mold of the connecting skirt winding tool. The area that overlaps with the inner layer of the skirt is finally formed into the connecting skirt segment.

[0015] Step 4: Installation of test base winding fixture and fiber winding

[0016] The test base is formed by winding a resin-impregnated composite material with existing winding tooling. The composite material layup of the test base adopts a quasi-isotropic layup.

[0017] Step 5: Wrap the outer skin of the shell and connecting skirt together.

[0018] The shell and connecting skirt are wrapped with an integral outer skin, and the composite material layup of the integral outer skin is circumferential.

[0019] Step Six: After winding, the shell and connecting skirt are cured and formed as a single unit.

[0020] After the outer skin is wrapped, it is placed in the oven for curing. It is treated at 90-100℃ for 1.5-2.5 hours, at 120-130℃ for 2-4 hours, and at 140-160℃ for 6-10 hours.

[0021] Step 7: Demolding and trimming of the prepared parts

[0022] The surface of the cured and molded part is polished to remove burrs. Before use, the shell winding fixture and the connecting skirt winding fixture are coated with a film agent to facilitate demolding of the part.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with the traditional method of manufacturing the engine housing and connecting skirt separately and then assembling them, the present invention forms the connecting skirt during the engine housing forming process, and co-cures the housing and connecting skirt with composite materials, which reduces manufacturing time and eliminates the machining process of the connecting skirt, simplifies the interface structure and manufacturing process, ensures the consistency between the housing and the connecting skirt, improves the connection strength and load-bearing capacity compared with the traditional assembly, the integrated structure has higher reliability, ensures higher sealing performance in the connection area between the connecting skirt and the housing, improves the axial load-bearing capacity of the housing, and the axial compression test shows that its ultimate axial compression load can reach 1100KN. The overall processability is good, the manufacturing time is short, and the prepared finished product has better mechanical properties. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of the integrated structure of the rocket engine composite shell and connecting skirt of the present invention;

[0025] Figure 2 This is a cross-sectional view of the overlap area between the housing and the connecting skirt of the present invention;

[0026] Figure 3 This is a schematic diagram of the shell winding tool of the present invention;

[0027] Figure 4 This is a schematic diagram of the connecting skirt winding fixture of the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] like Figures 1-4 As shown, an integrated structure of a rocket engine composite shell and connecting skirt includes a test base 1, a shell 2, and a connecting skirt 3.

[0030] Combination Figure 1As shown, the shell 2 is a hollow cavity made of composite fiber cloth. The diameter difference between the two ends of the hollow cavity makes it conical in shape. It is divided into an inner cylinder section 4, which is conical in the middle, and a joint and a cap 5, which are spherical at both ends and have reserved central holes. The joint is located at the small diameter end of the inner cylinder section 4, and the cap 5 is located at the large diameter end of the inner cylinder section 4. The test base 1 is made of composite material and is integrally set at one end of the joint of the shell 2 for subsequent axial compression test. The connecting skirt 3 is made of composite material and is connected to one end of the cap 5 of the shell 2 through the overlap area to form a whole.

[0031] Combination Figure 2 As shown, the overlapping area includes a connecting skirt 3 overlapping a connecting skirt segment 7 on the inner cylinder segment 4 and a skirt inner layer 6 evenly laid between the connecting skirt segment 7 and the shell 2.

[0032] Combination Figure 3 As shown, the shell winding fixture used when winding the shell 2 includes a mandrel 8, a winding inner cylinder 9, a sealing valve 10, a joint positioning sleeve 11, and a sealing valve positioning sleeve 12. The winding inner cylinder 9 is coaxially mounted in the middle of the mandrel 8. The outer contour of the winding inner cylinder 9 cooperates with the inner cylinder section 4 for winding and shaping the inner cylinder section 4 of the shell 2. The joint positioning sleeve 11 and the sealing valve positioning sleeve 12 are rotatably mounted on both sides of the mandrel 8 for positioning the joint valve and the sealing valve 10 on the mandrel 8. The joint valve and the sealing valve 10 are coaxially mounted on the joint positioning sleeve 11 and the sealing valve positioning sleeve 12 and are connected to both ends of the winding inner cylinder 9 for winding and shaping the joint and the sealing valve 5 of the shell 2.

[0033] The outer wall of the mandrel 8 has pre-machined steps at corresponding positions to the joint positioning sleeve 11 and the end cap positioning sleeve 12 for the installation and positioning of the other components. The joint valve and the end cap valve 10 are both welded from several petals. The two ends of the winding inner cylinder 9 are installed with the joint valve and the end cap valve 10 through grooves.

[0034] Combination Figure 4 As shown, the connecting skirt winding fixture used when winding the connecting skirt 3 includes a positioning inner sleeve 13 and a segmenting mold 14. The positioning inner sleeve 13 is rotatably mounted on the mandrel 8 to determine the relative position between the connecting skirt 3 and the end cap 5 of the housing 2 and to fix the segmenting mold 14. The segmenting mold 14 is fitted and fixed on the outside of the positioning inner sleeve 13, and its outer wall is pre-processed with grooves for laying composite materials in the transverse and longitudinal directions to complete the mesh reinforcement winding of the connecting skirt 3.

[0035] like Figures 1-4 As shown, a method for molding an integrated structure of a rocket engine composite shell and connecting skirt includes the following steps:

[0036] Step 1: Wrapping the shell composite material

[0037] After the shell winding fixture is installed, the shell 2 is wound circumferentially and longitudinally using resin-impregnated composite fiber cloth (preferably carbon fiber cloth). During the longitudinal winding process, fibers are reserved at one end of the inner cylinder 9 corresponding to the end cap valve 10. When the connecting skirt section 7 is formed later, some of the reserved fibers are laid in the structural layer of the connecting skirt 3 to form the skirt inner layer 6. During the circumferential winding process, the winding width is gradually increased to be the same as the width between the joint valve and the edge of the end cap valve 10 of the shell winding fixture.

[0038] Composite fiber cloth is a fiber-reinforced composite material. The material itself should meet the following principles: product performance, high specific strength and specific stiffness, compatibility of the material with the service environment of the structure, special structural requirements, processability requirements, low cost, and high efficiency.

[0039] Furthermore, the layup should consider the load conditions to meet the principle of balanced and symmetrical layup and the layup orientation should follow the load-bearing orientation principle. The circumferential layup angle of shell 2 is 90°, and the layup quantity accounts for 20%. The longitudinal layup angle is ±23°, and the layup quantity accounts for 80%.

[0040] Step 2: Reinforce and wrap the connecting skirt mesh

[0041] After the connecting skirt winding fixture is installed, the connecting skirt 3 is wound with mesh reinforcement using composite materials. The longitudinal reinforcing fibers in the mesh reinforcement are taken from the remaining reserved fibers during the longitudinal winding process of the shell 2. The transverse reinforcing fibers in the mesh reinforcement are made of composite materials. The thickness of the longitudinal and transverse reinforcing fibers is ensured to be the same as the depth of the transverse and longitudinal grooves reserved on the outer side wall of the segmented mold 14 of the connecting skirt winding fixture. The layup angle of the mesh reinforcement composite material is based on the reinforcement direction.

[0042] Step 3: Connecting the skirt skin and wrapping it

[0043] The skin of the connecting skirt 3 is wound by wrapping a resin-impregnated composite material around the outside of the reinforcing mesh of the connecting skirt, starting from one end of the shell 2 and continuing until it is flush with the step reserved at the end of the segmented mold 14 of the connecting skirt winding fixture. The area that overlaps with the inner layer 6 of the skirt is finally formed into the connecting skirt segment 7. To ensure uniform skin tension, the selected composite material should be kept under uniform tension during circumferential winding. Low-twist, uniformly tensioned fibers are recommended as the composite material for skin winding, and the fibers within the yarn sheet should be kept as parallel as possible during skin winding. The fiber tension is generally controlled at 1 kg.

[0044] Step 4: Installation of test base winding fixture and fiber winding

[0045] The test base 1 is formed by winding a composite material impregnated with resin using an existing winding tooling. The composite material layup of the test base 1 is a quasi-isotropic layup.

[0046] Step 5: Wrap the outer skin of the shell and connecting skirt together.

[0047] The shell 2 and the connecting skirt 3 are wrapped with an integral outer skin, and the composite material layup of the integral outer skin is circumferential.

[0048] Step Six: After winding, the shell and connecting skirt are cured and formed as a single unit.

[0049] After the outer skin is wrapped, it is placed in an oven for curing. It is treated at 90-100℃ for 1.5-2.5 hours, at 120-130℃ for 2-4 hours, and at 140-160℃ for 6-10 hours.

[0050] Step 7: Demolding and trimming of the prepared parts

[0051] The surface of the cured and molded part is polished to remove burrs. Before use, the shell winding fixture and the connecting skirt winding fixture are coated with a film agent to facilitate demolding of the part.

[0052] The amount of adhesive in the prepared parts of this invention is determined according to the application requirements. The volumetric adhesive content of the composite material ranges from 35% to 45%, with 40% being optimal. Furthermore, during the impregnation process, the temperature of the adhesive bath should be controlled to adjust the resin viscosity. For resin matrices that cure at high temperatures, the adhesive bath temperature should be controlled at around 40°C; for resin matrices that cure at room temperature, the adhesive bath temperature should be controlled at around 20°C. To ensure sufficient impregnation of the composite material, uniform resin content, and maximum escape of air bubbles, the resin viscosity should be as low as possible, typically within the range of 0.35-1.0 Pa·s. Appropriate heating temperatures and volatile solvents can be selected, or active diluents can be used instead of ordinary solvents. Drying or other measures can be employed to process the impregnated composite material.

[0053] In the curing process of this invention, the heating phase requires a steady and not too rapid heating. Otherwise, due to the intense chemical reaction, low-molecular-weight substances such as solvents will rapidly evaporate, forming a large number of bubbles. When the temperature is below the boiling point of the components, the heating rate must be controlled to expel the bubbles. After the boiling point, the heating rate can be appropriately increased. Excessive heating of the composite material part will lead to large temperature differences between different parts of the product. In particular, to ensure the internal part reaches the reaction temperature, the outer layer may be heated too high and cured prematurely. This results in two consequences: firstly, internal volatiles cannot be released, leading to defects within the part; secondly, significant internal stress will be generated. Both of these directly affect the physicochemical and mechanical properties of the part. Similarly, the cooling rate during the curing phase should not be too rapid. Since the coefficient of linear expansion in the fiber direction and its perpendicular direction differs by nearly four times, excessive cooling will cause uneven shrinkage in different directions and parts of the part, generating excessive internal stress, which will also reduce the performance of the part and even lead to cracking. Therefore, through practice and summarization, the inventors concluded that the heating and cooling rates of the composite material preparation parts during the curing stage in the method of the present invention should be controlled at 1-2℃ / min.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0055] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An integrated structure of a rocket engine composite shell and connecting skirt, characterized in that: The test base (1), the shell (2) and the connecting skirt (3), the shell (2) is a hollow cavity made of composite fiber cloth winding, the difference between the two ends of the hollow cavity exists in the diameter, so that the whole is conical, divided into a inner cylinder segment (4) in the middle part of the conical and a integral setting in both ends of the spherical shell and reserving the center hole joint and head (5), the joint is set in the small diameter end of the inner cylinder segment (4), the head (5) is set in the large diameter end of the inner cylinder segment (4), the test base (1) is made of composite material winding and is integrally arranged at the joint end of the shell (2) for subsequent axial compression test, the connecting skirt (3) is made of composite material winding and is integrally connected with the one end of the head (5) of the shell (2) through the lap joint area, the lap joint area includes the connecting skirt segment (7) of the connecting skirt (3) lapped on the inner cylinder segment (4) and the in-skirt layer (6) uniformly laid between the connecting skirt segment (7) and the shell (2), the formation of the in-skirt layer (6) is that the composite material fiber cloth soaked in glue is used for circumferential winding and longitudinal winding of the shell (2), during the longitudinal winding, the fiber is reserved at one end and part of the reserved fiber is laid in the structure layer of the connecting skirt (3) when the connecting skirt segment (7) is formed subsequently.

2. The integrated structure of the composite case and the connecting skirt of a rocket engine according to claim 1, characterized in that: The shell winding tool used during the winding of the shell (2) includes the mandrel (8), the winding inner cylinder (9), the head valve (10), the joint positioning sleeve (11) and the head positioning sleeve (12), the mandrel (8) is coaxially sleeved with the winding inner cylinder (9) at the middle position, the outer contour of the winding inner cylinder (9) is matched with the inner cylinder segment (4) for winding and forming of the inner cylinder segment (4) of the shell (2), the joint positioning sleeve (11) and the head positioning sleeve (12) are respectively rotationally installed on both sides of the mandrel (8) for positioning of the joint valve and the head valve (10) on the mandrel (8), the joint valve and the head valve (10) are respectively coaxially installed on the joint positioning sleeve (11) and the head positioning sleeve (12) and are abutted on both ends of the winding inner cylinder (9) for winding and forming of the joint and the head (5) of the shell (2).

3. The integrated structure of the composite case and the connecting skirt of a rocket engine according to claim 2, characterized in that: The connecting skirt winding tool used during the winding of the connecting skirt (3) includes the positioning inner sleeve (13) and the split mold (14), the positioning inner sleeve (13) is rotationally installed on the mandrel (8) for determining the relative position between the connecting skirt (3) and the head (5) of the shell (2) and plays a fixing role on the split mold (14), the split mold (14) is fixedly sleeved on the outside of the positioning inner sleeve (13) and the outside wall thereof is reserved for processing grooves for transverse and longitudinal laying of composite material, so as to complete the grid reinforced winding of the connecting skirt (3).

4. A forming method of a rocket engine composite case and integrated structure of a connecting skirt, characterized by: The forming method of the rocket engine composite shell and connecting skirt integrated structure according to claim 3 comprises the following steps: Step one: composite material winding of the shell After the shell winding tool is installed, the shell (2) is wound with impregnated composite fiber cloth in the hoop direction and in the longitudinal direction, and during the longitudinal winding, the fiber is reserved at the corresponding end of the winding inner cylinder (9) and the head valve (10), and part of the reserved fiber is laid in the connecting skirt (3) structure layer to form the in-skirt layup (6) when the connecting skirt (7) is subsequently formed and connected. During the hoop winding, the winding width is gradually increased to the same width as the joint valve and the edge of the head valve (10) of the shell winding tool. Step two: connecting skirt grid reinforced winding After the connecting skirt winding tool is installed, the connecting skirt (3) is grid reinforced with composite material, the longitudinal reinforcing fiber in the grid reinforcement is taken from the remaining reserved fiber in the longitudinal winding of the shell (2), and the transverse reinforcing fiber in the grid reinforcement is made of fiber made of composite material, the thickness of the longitudinal reinforcing fiber and the transverse reinforcing fiber is the same as the depth of the transverse and longitudinal grooves reserved and processed on the outside wall of the split mold (14) of the connecting skirt winding tool, and the angle of the grid reinforced composite material layup is taken as the reference direction of the reinforcing direction; Step three: connecting skirt skin winding The skin winding of the connecting skirt (3) is performed, and the impregnated composite material is wound in the hoop direction from the outside of the shell (2) to the step reserved at the end of the split mold (14) of the connecting skirt winding tool, wherein the area coinciding with the in-skirt layup (6) is finally formed into the connecting skirt segment (7); Step four: test base winding tool installation and fiber winding The test base (1) is wound and formed using impregnated composite material combined with existing winding tools, and the composite material layup of the test base (1) is quasi-isotropic layup; Step five: overall outer skin of the wound shell and connecting skirt The overall outer skin of the shell (2) and the connecting skirt (3) is wound, and the composite material layup of the overall outer skin is oriented in the hoop direction; Step six: integrated solidification of the shell and the connecting skirt after winding After the overall outer skin winding is completed, the solidification is carried out in the oven, 90~100℃ for 1.5~2.5h, 120~130℃ for 2~4h, and 140~160℃ for 6~10h; Step seven: preparation piece demolding and finishing The surface of the solidified preparation piece is polished to remove burrs, and the surfaces of the shell winding tool and the connecting skirt winding tool are coated with a coating agent before use to facilitate the demolding of the preparation piece.

5. The method of claim 4, wherein the method further comprises: forming the skirt by: forming a first layer of the skirt; and forming a second layer of the skirt on the first layer of the skirt. In step one, the hoop layup angle of the shell (2) is 90°, the number of layups accounts for 20%, the longitudinal layup angle is ±23°, and the number of layups accounts for 80%.

6. The method of claim 4, wherein the method further comprises: forming the skirt by: forming a first layer of the skirt; and forming a second layer of the skirt on the first layer of the skirt. In step three, the fiber tension in the connecting skirt skin is controlled at 1kg.

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