Gradient wave-transparent heat shield forming method

Abstract

The application provides a gradient wave-transparent heat shield forming method, comprising the following steps: S1, preparing a preform of a heat shield; S2, configuring ceramic slurry; S3, fusing the ceramic slurry into the preform of the heat shield to form a green body of the heat shield; S4, placing the green body of the heat shield into the ceramic slurry to densify the green body of the heat shield; and S5, sealing a large port of the green body of the heat shield and performing solution infiltration on the green body of the heat shield by using polytetrafluoroethylene to form the heat shield. The heat shield prepared by the method not only has the functions of bearing and transmitting waves, but also has excellent heat insulation and heat protection functions.

Description

Technical Field

[0001] This invention relates to the field of ceramic-based microwave-transparent composite materials, and more specifically to a method for molding a gradient microwave-transparent heat insulation cover. Background Technology

[0002] A wave-transparent heat shield is also a type of radome, integrating multiple functions such as heat protection, load-bearing, and wave transmission. It is a structurally and functionally integrated component. Its purpose is to maintain an aerodynamic shape and protect the antenna system so that it can function normally in harsh environments.

[0003] As aircraft speeds increase, the resulting aerodynamic and thermal loads become extremely severe. The high-temperature resistant, wave-transparent ceramic materials commonly used in aircraft radomes are no longer sufficient to meet the requirements for high-temperature ablation resistance. Under high temperature and pressure, significant ablation occurs, especially at the nose, and prolonged heat penetration into the radome severely impacts its operation. Ablation not only alters the aerodynamic shape but also affects the radome's wave transmission performance. To ensure that the radome transmits electromagnetic waves with minimal distortion under aerodynamic heating conditions, it needs superior heat protection and insulation capabilities. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for forming a gradient wave-transparent heat insulation cover.

[0005] This invention provides a method for molding a gradient wave-transparent heat insulation cover, comprising:

[0006] S1. Prefabricate the heat insulation cover;

[0007] S2. Prepare ceramic slurry;

[0008] S3. The ceramic slurry is impregnated into the preform of the heat insulation cover to form the blank of the heat insulation cover;

[0009] S4. Place the unglazed blank of the heat insulation cover into the ceramic slurry to further densify the unglazed blank of the heat insulation cover.

[0010] S5. The large port of the blank of the sealed heat insulation cover is formed by dissolving and infiltrating polytetrafluoroethylene into the blank of the heat insulation cover to form a heat insulation cover with cooling function.

[0011] Further, step S1 includes:

[0012] The heat insulation cover consists of an inner layer, a middle layer, and an outer layer. Mullite fiber cloth is laid on a molded core, and the seams of each fiber cloth are sewn with mullite fiber to form the inner layer.

[0013] A layer of low-density quartz fiber cloth is laid on the inner layer, and the seams of each layer of quartz fiber cloth are sewn with quartz fiber to form an intermediate layer.

[0014] High-warp density quartz fiber cloth is laid on the basis of the intermediate layer, and the seams of each layer of quartz fiber cloth are sewn with quartz fiber. After reaching the designed thickness, high-warp density quartz fiber is used to make overall through sewing to form the prefabricated body of the heat insulation cover.

[0015] Furthermore, in step S1, during the process of laying low-density quartz fiber cloth on the inner layer, a layer of quartz fiber mesh is sandwiched between each layer of quartz fiber cloth, that is, a unit of one layer of cloth + one layer of mesh is repeatedly laid.

[0016] Further, in step S1, the mullite fiber is Nextel 720 grade; the low-warp, high-density quartz fiber cloth has a warp density of 3-4 threads / cm and a weft density of 2-3 threads / cm. The quartz fiber yarn in the low-warp, high-density quartz fiber cloth is 190tex type B hollow quartz fiber yarn, and the hollowness of the hollow quartz fiber yarn reaches more than 30%. The structure of the low-warp, high-density quartz fiber cloth is an eight-end, five-fly satin weave structure, and the areal density of the quartz fiber mesh is 25-35 g / m². 2 The high-warp, high-density quartz fiber fabric has a warp density of 9-10 threads / cm and a weft density of 7-8 threads / cm. The quartz fiber yarn used in this fabric is 190tex type B solid quartz fiber yarn, and the fabric has an eight-end, five-ply satin weave structure. The solid quartz fiber used for sewing has a specification of 190tex × 3-6 strands.

[0017] Furthermore, in step S1, the thickness ratio of the inner layer, middle layer, and outer layer of the heat insulation cover is 1:2:1.

[0018] Further, step S2 includes: preparing and mixing silica sol and aluminum sol in a certain mass ratio, adding cleaned quartz fibers and stirring thoroughly to form a ceramic slurry.

[0019] Further, step S3 includes: performing vacuum heat treatment on the preform to remove organic matter and impurities from the fiber surface, pouring ceramic slurry into the inner cavity of the preform, and centrifuging the preform using a centrifuge to allow the ceramic slurry to penetrate into the preform, forming a green body.

[0020] Further, step S4 includes: immersing the green body in ceramic slurry under vacuum multiple times until the density reaches the designed density, and then sintering the green body.

[0021] Further, step S5 includes: sealing the large end of the densified blank, evacuating the inner cavity of the blank and immersing it in a polytetrafluoroethylene emulsion, and drying it after immersion for a certain period of time to form a heat insulation cover with polytetrafluoroethylene infiltrated in the outer layer and part of the middle layer.

[0022] Furthermore, in step S5, the immersion time is determined based on the outer layer thickness of the heat insulation cover, and the immersion time h = outer layer thickness × (1.2~1.5).

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The heat insulation cover molding method of this invention produces a heat insulation cover with a gradient structure of dense inner and outer layers and a loose middle layer. The inner layer uses high-strength mullite fiber, giving it high load-bearing capacity, the middle layer provides heat insulation, and the outer layer resists high-temperature erosion. This effectively improves the load-bearing capacity, heat insulation, and ablation resistance of the heat insulation cover.

[0025] 2. This invention uses a preform of a polytetrafluoroethylene (PTFE) solution-infiltrated heat shield. During flight, the PTFE sublimates and absorbs heat, effectively reducing the temperature of the heat shield and providing semi-active cooling, thus significantly reducing surface ablation. Furthermore, PTFE has an extremely low dielectric constant, meaning that solution infiltration has virtually no impact on the product's wave transmission performance.

[0026] 3. This invention employs a centrifugal impregnation method for ceramic slurry, and the three-layer structure is integrally formed, which effectively improves the impregnation efficiency, achieves rapid densification of composite ceramics, and reduces the cost of the heat insulation cover.

[0027] 4. The three-layer variable density structure of the present invention can be applied to wideband wave transmission of radomes. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the wave-transparent heat insulation cover of the present invention.

[0029] Reference numerals: outer layer 1; middle layer 2; inner layer 3. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0031] like Figure 1 As shown, the heat insulation cover of this embodiment includes a three-layer structure, namely an inner layer 3, a middle layer 2, and an outer layer 1, which are integrally formed.

[0032] The molding methods for heat shields include:

[0033] S1. Prefabricating the heat insulation cover; specifically including:

[0034] A contour mold is made according to the inner surface of the product. Based on the structural dimensions and thickness of the inner layer 3, mullite fiber cloth is cut into fan shapes of different sizes. Then, layers are laid on the contour mold, and the seams of each fiber cloth layer are sewn together with mullite fiber to form the inner layer 3. In this embodiment, the inner layer 3 of the preform uses Nextel 720 grade mullite fiber, which utilizes its high modulus and high strength characteristics to improve the product strength.

[0035] After the inner layer 3 reaches the set thickness, the intermediate layer 2 is laid out using the same method. The intermediate layer 2 is made of low-warp density quartz fiber cloth, and the seams of each layer of low-warp density quartz fiber cloth are sewn with quartz fiber. A layer of quartz fiber mesh is sandwiched between each layer of low-warp density quartz fiber cloth. In this embodiment, the low-warp density quartz fiber cloth used in the intermediate layer 2 has a warp density of 3-4 threads / cm and a weft density of 2-3 threads / cm. The quartz fiber yarn is 190tex B-type hollow quartz fiber yarn. The structure of the low-warp density quartz fiber cloth is an eight-end five-ply satin weave structure, and the areal density of the quartz fiber mesh is 25-35 g / m². 2 The intermediate layer 2 is made of low-density fiber cloth and quartz mesh, which gives the intermediate layer 2 a low density and high porosity, thus achieving high thermal insulation performance of the product.

[0036] The outer layer 1 is laid out using the same method. The outer layer 1 is made of high-warp, high-density quartz fiber cloth, and the seams of each layer of high-warp, high-density fiber cloth are sewn together with quartz fiber. After reaching the set thickness, the entire structure is sewn together with quartz fiber to form the prefabricated heat shield. In this embodiment, the quartz fiber cloth used in the outer layer 1 has a warp density of 9-10 threads / cm and a weft density of 7-8 threads / cm. The quartz fiber yarn is 190tex type B solid quartz fiber yarn with an eight-end five-fly satin weave structure.

[0037] The spacing between the through-suture lines is 6-8 mm, and the fiber volume content of the preform after overall molding is 31-35%. At the same time, the three-layer variable density structure is conducive to the realization of broadband wave transmission performance.

[0038] In this embodiment, the thickness ratio of the inner layer 3, the middle layer 2, and the outer layer 1 of the prefabricated heat insulation cover is 1:2:1.

[0039] S2. Preparing ceramic slurry; specifically including:

[0040] A mixture of 40% solids silica sol and 60% solids aluminum sol was prepared and thoroughly mixed at a mass ratio of 5:1. Then, 1.2%–2.5% by mass of whisker-like quartz fibers (≤1 mm in length and 7.5 μm ± 1 μm in diameter) was weighed out. The quartz fibers were soaked in acetone for 3–5 hours and then sonicated for 30–40 minutes. They were then cleaned with ethanol and sonicated for another 30–40 minutes, followed by microwave drying for 1–2 hours. Finally, the quartz fibers were added to the silica sol and aluminum sol mixture, stirred at high speed for 30 minutes, and sonicated for 1–1.5 hours to ensure complete dispersion. The mixture was then allowed to stand at room temperature for 1–2 hours before use.

[0041] S3. Impregnating the ceramic slurry into the preform of the heat insulation cover to form the blank of the heat insulation cover; specifically including:

[0042] The prepared preform is placed in a vacuum heat treatment furnace and heat-treated at 410℃~510℃ for 1h~2h under vacuum conditions to remove organic matter and impurities from the fiber surface. Then, the preform is placed tip-down into an inverted conical centrifuge. The prepared ceramic slurry is poured into the inner cavity of the preform, with the liquid level of the ceramic slurry flush with the large end face of the preform. The centrifuge lid is closed, and the preform is transferred to a vacuum chamber. A vacuum is drawn, and the pressure is maintained below -95kPa for at least 30min. The centrifuge is then turned on for centrifugation for 2h~3h. The centrifuged preform is then placed in a microwave drying oven and dried at 100℃~150℃ for 1℃~1.5℃. The resulting green preform is then obtained.

[0043] S4. Place the unglazed blank of the heat insulation cover into the ceramic slurry to further densify the unglazed blank of the heat insulation cover; specifically including:

[0044] The prepared green body is placed in ceramic slurry and impregnated under vacuum, maintaining an ambient pressure below -95 kPa for at least 10–15 hours. The green body is then removed and placed in a microwave drying oven at 100–150℃ for 1–1.5 hours. This vacuum impregnation method is repeated 2–3 times until the density reaches 1.7–1.75 g / cm³. 3 Then, it is placed in a sintering furnace and sintered at 900–1050℃ for 2.5–3.5 hours. Finally, the densified green blank is machined to the designed dimensions.

[0045] S5. The large port of the unglazed heat insulation cover is formed by solvent infiltration of polytetrafluoroethylene (PTFE) into the unglazed heat insulation cover to create a heat insulation cover with cooling function; specifically including:

[0046] Polytetrafluoroethylene (PTFE) is used as a solvent, and PTFE is dissolved into the preform in the form of a PTFE emulsion. The PTFE emulsion is a white aqueous dispersion with a solid content of 58% and a particle size of less than 200 nm. The large end of the densified preform is sealed with a tooling, and the inner cavity of the preform is evacuated and immersed in the PTFE emulsion. After immersion for a certain period of time (the immersion time can be determined according to the thickness of the outer layer 1 of the heat shield, immersion time h = outer layer 1 thickness (mm) × (1.2~1.5h)), it is taken out and left to air dry at room temperature for 3~5h. Then, it is dried at 150℃~200℃ for 5h~6h to form a heat shield with outer layer 1 and part of the middle layer 2 dissolved in PTFE.

[0047] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for forming a gradient wave-transparent heat insulation cover, characterized in that: include: S1. Prefabricate the heat insulation cover; S2. Prepare ceramic slurry; S3. The ceramic slurry is impregnated into the preform of the heat insulation cover to form the blank of the heat insulation cover; S4. Place the unglazed blank of the heat insulation cover into the ceramic slurry to further densify the unglazed blank of the heat insulation cover. S5. The large port of the blank of the sealed heat insulation cover is formed by dissolving and infiltrating polytetrafluoroethylene into the blank of the heat insulation cover to form a heat insulation cover with cooling function. Step S1 includes: The heat insulation cover includes an inner layer (3), a middle layer (2), and an outer layer (1). Mullite fiber cloth is laid on the mold, and the overlap of each layer of fiber cloth is sewn with mullite fiber to form the inner layer (3). Low-density quartz fiber cloth is laid on the inner layer (3), and the seams of each layer of quartz fiber cloth are sewn with quartz fiber to form the middle layer (2). High-warp density quartz fiber cloth is laid on the basis of the intermediate layer (2), and the seams of each layer of quartz fiber cloth are sewn with quartz fiber. After reaching the designed thickness, high-warp density quartz fiber is used for overall through sewing to form the prefabricated heat insulation cover. In step S1, during the process of laying low-density quartz fiber cloth on the inner layer (3), a layer of quartz fiber mesh is sandwiched between each layer of quartz fiber cloth. In step S1, the mullite fiber is Nextel 720 grade; the low-warp, high-density quartz fiber cloth has a warp density of 3-4 threads / cm and a weft density of 2-3 threads / cm; the quartz fiber yarn of the low-warp, high-density quartz fiber cloth is 190tex type B hollow quartz fiber yarn; the structure of the low-warp, high-density quartz fiber cloth is an eight-end, five-fly satin weave structure; and the areal density of the quartz fiber mesh is 25-35 g / m². 2 The warp density of the high-warp quartz fiber cloth is 9-10 threads / cm, and the weft density is 7-8 threads / cm. The quartz fiber yarn of the high-warp quartz fiber cloth is 190tex type B solid quartz fiber yarn. The structure of the high-warp quartz fiber cloth is an eight-end five-fly satin structure. In step S1, the thickness ratio of the inner layer (3), middle layer (2), and outer layer (1) of the heat insulation cover is 1:2:

1.

2. The method for forming a gradient wave-transparent heat insulation cover according to claim 1, characterized in that: Step S2 includes: preparing and mixing silica sol and aluminum sol in a certain mass ratio, adding cleaned quartz fibers and stirring thoroughly to form a ceramic slurry.

3. The method for forming a gradient wave-transparent heat insulation cover according to claim 1, characterized in that: Step S3 includes: performing vacuum heat treatment on the preform to remove organic matter and impurities from the fiber surface, pouring ceramic slurry into the inner cavity of the preform, and centrifuging the preform using a centrifuge to allow the ceramic slurry to penetrate into the preform, forming a green body.

4. The method for forming a gradient wave-transparent heat insulation cover according to claim 1, characterized in that: Step S4 includes: immersing the green body in ceramic slurry under vacuum multiple times until the density reaches the designed density, and then sintering the green body.

5. The method for forming a gradient wave-transparent heat insulation cover according to claim 1, characterized in that: Step S5 includes: sealing the large end of the densified blank, evacuating the inner cavity of the blank and immersing it in polytetrafluoroethylene emulsion, drying it after immersion for a certain period of time, and forming an outer layer (1) and a partial middle layer (2) of a heat insulation cover infiltrated with polytetrafluoroethylene.

6. The method for forming a gradient wave-transparent heat insulation cover according to claim 5, characterized in that: In step S5, the immersion time is determined based on the thickness of the outer layer (1) of the heat insulation cover. The immersion time h = outer layer thickness × (1.2~1.5).

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