Supporting tool and method for thin-wall large-length-diameter-ratio composite pipe fitting CVI process

Abstract

The invention discloses a supporting tool and method for a thin-wall large-length-diameter-ratio composite pipe fitting CVI technology, belongs to the technical field of ceramic matrix composite pipe fitting preparation, and solves the problems that in the prior art, when vapor deposition is carried out on a composite pipe fitting, a full-mold or half-mold restraining tool is adopted, diffusion and transmission of reaction gas into a prefabricated body are restrained, and the reaction time is shortened. And the deposition rate of the pipe fitting is too high. The supporting tool comprises a bottom template, a supporting round rod and a supporting graphite cap. According to the invention, the bottom template is used as a tool foundation, provides reference planeness and ensures straightness support in the horizontal direction; the supporting round rod and the supporting graphite cap which are used for supporting the ceramic-based composite pipe fitting are installed on the bottom template, reaction gas can penetrate through a gap between the supporting round rod and the supporting graphite cap in the deposition process, the deposition surface area of the pipe fitting is exposed to the maximum degree, and therefore the permeation efficiency and the deposition rate of the reaction gas in the CVI technological process are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic matrix composite pipe preparation, and particularly relates to a support tool and method for CVI process of thin-walled large-length-diameter-ratio composite pipe. BACKGROUND

[0002] Ceramic matrix composites (CMCs) have important application potential in key fields such as aerospace, energy and chemical industry due to their excellent high specific strength, high specific modulus, high temperature resistance and corrosion resistance. As a core structural component, the performance and quality of a thin-walled ceramic matrix composite pipe directly determine the reliability and service life of related equipment. However, the thin-walled ceramic matrix composite pipe is prone to deformation during preparation, so effective support tools and preparation processes must be relied on to ensure its dimensional accuracy and quality. At present, the main thin-walled ceramic matrix composite pipe preparation methods include chemical vapor infiltration (CVI), precursor infiltration and pyrolysis (PIP) and reactive melt infiltration (RMI).

[0003] For thin-walled, large-length-diameter-ratio ceramic matrix composite pipes, the two commonly used deposition processes, PIP (precursor infiltration and pyrolysis) and RMI (reactive melt infiltration), have significant inherent disadvantages in application. The core problem of the PIP process is its low efficiency and the introduction of internal defects. The process relies on the impregnation of a liquid ceramic precursor into a fiber preform and then pyrolysis at high temperature to convert it into a ceramic matrix. However, the ceramic yield of a single pyrolysis is low, and the volume shrinks greatly, so multiple impregnation-curing-pyrolysis cycles must be performed to achieve the required densification. Long cycles result in high production costs and high energy consumption, and the uneven shrinkage in each cycle accumulates a large amount of residual stress in the component. For thin-walled pipes with delicate structures and low stiffness, this stress easily causes irreversible twisting and bending deformation, seriously affecting the dimensional accuracy and mechanical properties.

[0004] In contrast, the disadvantages of the RMI process (reaction infiltration method) mainly lie in the damage of the material in the high-temperature chemical environment. The process realizes rapid densification by infiltrating molten metal (such as silicon) into a carbon-containing preform to react (such as Si + C → SiC), and the cycle is much shorter than PIP. However, the extremely high reaction temperature (usually more than 1400°C) and the direct contact of the molten metal can seriously damage the carbon fibers, significantly reduce their strength, and thus affect the overall mechanical properties of the composite pipe. At the same time, the thermal stress in the process of exothermic reaction and cooling and the volume change caused by chemical reaction can also produce residual stress and deformation. In addition, the matrix generated by the reaction (such as SiC) will be unevenly distributed, and there may be concentrated areas of coarse ceramic particles and unreacted metal, resulting in a decrease in material performance.

[0005] The CVI process is essentially an extension of the chemical vapor deposition (CVD) technique, and is a material densification process based on gas-solid surface heterogeneous chemical reaction. Since ceramic matrix composites are difficult to be formed in one step to prepare large-size components with complex shapes, breakthrough in deposition processing technology is one of the key challenges to realize wide application. In particular, for thin-walled ceramic matrix composite pipes with a large aspect ratio, maintaining their straightness during CVI deposition densification is a core process problem that needs to be solved.

[0006] The current common solution is to use full or half mold constraint tooling. However, the wrapping of such molds significantly inhibits the diffusion and transport of the reaction gas to the inside of the preform, resulting in a significant extension of the deposition densification cycle; the deposition rate of thin-walled pipes is too slow, the production cycle is too long, and the production cost is significantly increased. In addition, the existing CVI tooling generally has complex structure, inconvenient operation, and low densification efficiency, which seriously restricts the preparation efficiency and final quality of thin-walled ceramic matrix composite pipes.

[0007] Therefore, it is of urgent need and great significance to develop a new type of support tooling suitable for CVI process of thin-walled ceramic matrix composite pipes and a supporting preparation method, in order to improve product quality, shorten production cycle, reduce cost and promote engineering application. SUMMARY

[0008] In view of the deficiencies in the prior art, the present application provides a support tooling and method for CVI process of thin-walled large-aspect-ratio composite pipe, which solves the problem of the prior art that the use of full or half mold constraint tooling during gas phase deposition of the composite pipe inhibits the diffusion and transport of the reaction gas to the inside of the preform, resulting in a slow deposition rate of the pipe.

[0009] In the first aspect, in order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is: The application discloses a support tool for a CVI process of a thin-walled large-length-diameter-ratio composite pipe, which comprises a bottom template, support round rods and support graphite caps; the bottom template is provided with a plurality of support round rods arranged in a rectangular array, and each support round rod is provided with a support graphite cap; the top of the support graphite cap is provided with a semicircular groove, and a ceramic matrix composite pipe is supported in the semicircular groove of the support graphite cap.

[0010] In the application, the bottom template serves as a tool base, and the core function thereof is to provide a reference flatness and ensure horizontal straightness support; the support round rods and the support graphite caps for supporting the ceramic matrix composite pipe are arranged on the bottom template, so that the deposition surface area of the pipe is maximally exposed, the reaction gas can pass through the gap between the support round rods and the support graphite caps during deposition, and the penetration efficiency of the reaction gas and the deposition rate in the CVI process are significantly improved.

[0011] Further, a plurality of mounting holes are arranged on the upper surface of the bottom template at a preset interval; and a boss structure is arranged at the bottom of the rod body of the support round rod, and the boss structure is vertically mounted in the mounting hole.

[0012] In the application, the mounting holes ensure consistent depth and good straightness of the coaxial holes, and lay a foundation for accurate positioning of the support round rods. The support round rods are vertically mounted in the mounting holes of the bottom template, a uniform mounting height reference is provided, and accurate straightness support in the vertical direction of the thin-walled large-length-diameter-ratio pipe placed thereon is ensured.

[0013] Further, the support graphite cap comprises a hollow cylinder and a semicircular support part, the bottom of the hollow cylinder is sleeved on the top of the support round rod, the top of the hollow cylinder is connected with the semicircular support part, and the semicircular groove in the top of the semicircular support part is used for supporting the ceramic matrix composite pipe.

[0014] In the application, the hollow cylinder is mounted on the top of the support round rod, and the mounting is simple and convenient for replacement; after CVI deposition, if the semicircular support part of the support graphite cap is adhered to the ceramic matrix composite pipe, the support graphite cap can be damaged, a new support graphite cap can be replaced, and the support graphite cap serves as a replacement part.

[0015] Further, the outer diameter of the hollow cylinder is 12 mm, and the inner diameter thereof is 8 mm; and the diameter of the semicircular groove in the top of the semicircular support part is 9.4 mm.

[0016] Further, the support graphite caps in each row are arranged at equal intervals along the length direction of the ceramic matrix composite pipe, the semicircular grooves in the top of the support graphite caps are in the same direction, and the ceramic matrix composite pipe is uniformly supported.

[0017] In the present scheme, the support graphite cap directly supports the ceramic matrix composite pipe to be processed; the top thereof is designed as a semicircular groove body accurately matching the curvature of the outer surface of the ceramic matrix composite pipe, so as to provide uniform support, effectively maintain the overall straightness of the ceramic matrix composite pipe, and maximize the deposition surface area of the pipe, thereby significantly improving the penetration efficiency and deposition rate of the reaction gas in the CVI process.

[0018] Further, the bottom template is a graphite template; the length of the graphite template is 1205mm, the width is 220mm, and the height is 40mm.

[0019] Further, the diameter of the support round rod is 8mm, and the height is 35mm; the bottom of the support round rod is provided with a 1mm boss; and the material of the support round rod is C / SiC composite material.

[0020] In the second aspect, the present application provides a support tool for the CVI process of a thin-walled large-length-diameter-ratio composite pipe based on the support tool for the CVI process of a thin-walled large-length-diameter-ratio composite pipe provided in the first aspect, and provides a use method of the support tool for the CVI process of a thin-walled large-length-diameter-ratio composite pipe, which comprises the following steps: S1: placing the bottom template on the workbench; and vertically inserting the support round rod into the mounting hole on the surface of the bottom template; S2: sleeving the hollow cylindrical sleeve of the support graphite cap on the top of the support round rod, and installing all the support graphite caps one by one; S3: calibrating the height of the installed support round rod and the orientation of the support graphite cap; S4: placing the ceramic matrix composite pipe with a diameter of 9.4mm to be processed by CVI on the support graphite cap; after placement, checking whether the outer surface of the pipe body is completely fitted with the contact surface of the semicircular groove body on the top of all the support graphite caps, and ensuring that there is no overhanging or local excessive stress; S5: placing the ceramic matrix composite pipe together with the support tool in the deposition furnace for deposition.

[0021] The present application has the following beneficial effects: In the CVI process for thin-walled, high aspect ratio composite pipes provided by this invention, the bottom template serves as the foundation, its core function being to provide a reference flatness and ensure horizontal straightness support. Supporting round rods and supporting graphite caps for supporting the ceramic-based composite pipes are installed on the bottom template. The supporting graphite caps directly support the ceramic-based composite pipes to be processed, and their tops are designed as semi-circular grooves precisely matching the curvature of the outer surface of the ceramic-based composite pipes to provide uniform support and effectively maintain the overall straightness of the ceramic-based composite pipes. During deposition, the reactive gas can pass through the gap between the supporting round rods and the supporting graphite caps, maximizing the exposure of the deposition surface area of ​​the pipe and significantly improving the permeation efficiency and deposition rate of the reactive gas during the CVI process. This solves the problem in existing technologies where full-mold or half-mold constraint fixtures suppress the diffusion and transmission of reactive gas into the preform during vapor deposition of composite pipes, leading to excessive deposition rates. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the support fixture for the CVI process of a thin-walled composite pipe fitting according to the present invention; Figure 2 This is a schematic diagram of the supporting circular rod in this invention; Figure 3 This is a schematic diagram of the structure supporting the graphite cap in this invention.

[0023] Figure label: 1. Bottom template; 11. Mounting holes; 2. Supporting round rod; 21. Boss structure; 3. Supporting graphite cap; 31. Hollow cylinder; 32. Semi-circular support part; Detailed Implementation The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Specific embodiments of the present invention are described below to facilitate understanding by those skilled in the art. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various modifications are obvious as long as they fall within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0024] Example 1 like Figure 1 As shown, this embodiment provides a support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings to improve the manufacturing quality and efficiency of ceramic matrix composite pipe fittings. Before using this support fixture, the ceramic matrix composite pipe fittings need to be PIP-shaped to prevent deformation during CVI deposition on this fixture. This solves the problem of excessively slow deposition rate and long product cycle time during the CVI deposition process of thin-walled, high aspect ratio ceramic matrix composite pipe fittings after shaping. Specifically, it includes: Bottom template 1, supporting round rod 2, and supporting graphite cap 3; The bottom template 1 has several rectangular arrayed support rods 2, each with a support graphite cap 3. The top of the support graphite cap 3 has a semi-circular groove, within which the ceramic-based composite tubing is supported. The bottom template 1 serves as the tooling base, its core function being to provide a reference flatness and ensure horizontal straightness support. The support rods 2 and support graphite caps 3 on the bottom template 1 maximize the exposure of the tubing's deposition surface area. During deposition, reactive gases can pass through the gap between the support rods 2 and support graphite caps 3, significantly improving the permeation efficiency and deposition rate of the reactive gases during the CVI process.

[0025] The upper surface of the bottom template 1 has several mounting holes 11 at preset intervals. For example... Figure 2 As shown, the bottom of the supporting round rod 2 is machined with a boss structure 21, which is vertically installed in the mounting hole 11. The mounting holes 11 ensure consistent depth and good straightness of the coaxial holes, laying the foundation for the precise positioning of the supporting round rod 2. The supporting round rod 2 is vertically installed in the mounting hole 11 of the bottom template 1, providing a uniform installation height benchmark and ensuring that the thin-walled, high length-to-diameter ratio pipe placed on it receives precise straightness support in the vertical direction.

[0026] like Figure 3 As shown, the supporting graphite cap 3 includes a hollow cylinder 31 and a semi-circular support portion 32. The bottom of the hollow cylinder 31 is fitted onto the top of the supporting rod 2; the top of the hollow cylinder 31 is connected to the semi-circular support portion 32, and the semi-circular groove at the top of the semi-circular support portion 32 is used to support the ceramic matrix composite pipe fitting. Using the hollow cylinder 31 installed on the top of the supporting rod 2 simplifies installation and facilitates replacement. Furthermore, if the semi-circular support portion 32 of the supporting graphite cap 3 adheres to the ceramic matrix composite pipe fitting after CVI deposition, the supporting graphite cap 3 can be destroyed and replaced with a new supporting graphite cap 3, serving as a replacement part.

[0027] The hollow cylinder 31 has an outer diameter of 12mm and an inner diameter of 8mm; the semi-circular groove at the top of the semi-circular support 32 has a diameter of 9.4mm.

[0028] Each row of supporting graphite caps 3 is arranged at equal intervals along the length of the ceramic matrix composite pipe. The semi-circular grooves on the top of the supporting graphite caps 3 are aligned in the same direction, providing uniform support to the ceramic matrix composite pipe. The supporting graphite caps 3 directly support the ceramic matrix composite pipe to be processed; their tops are designed as semi-circular grooves that precisely match the curvature of the outer surface of the ceramic matrix composite pipe to provide uniform support, effectively maintaining the overall straightness of the ceramic matrix composite pipe while maximizing the exposure of the deposition surface area of ​​the pipe, thereby significantly improving the permeation efficiency and deposition rate of the reactive gas during the CVI process.

[0029] The bottom template 1 is a graphite template; the graphite template is 1205mm long, 220mm wide, and 40mm high.

[0030] The diameter of the support rod 2 is 8mm and the height is 35mm; the bottom of the support rod 2 is provided with a 1mm boss; the material of the support rod 2 is C / SiC composite material.

[0031] Example 2 This embodiment, based on the support fixture for the CVI process of thin-walled composite pipe fittings with a large length-to-diameter ratio provided in Embodiment 1, provides a method for using the support fixture for the CVI process of thin-walled composite pipe fittings with a large length-to-diameter ratio, including the following steps: S1: Device preparation and installation; First, check the integrity of each component, including the bottom template 1, the supporting round rod 2, and the supporting graphite cap 3; Place the bottom template 1 stably on the workbench to ensure its stability; Insert the supporting round rod 2 vertically into the mounting hole 11 on the surface of the bottom template 1.

[0032] S2: Install the support graphite cap 3; fit the hollow cylinder 31 of the support graphite cap 3 onto the top of the support rod 2, and install the support graphite cap 3 one by one to the top of the support rod 2 to ensure that the graphite cap and the support rod 2 are in stable contact and completely fit together.

[0033] S3: Tooling calibration; Accurately calibrate the height of the installed support rod 2 and the orientation (angle) of the support graphite cap 3. This can be done using auxiliary tools (such as a standard stainless steel pipe with an infrared level) to ensure the straightness and levelness of the overall tooling.

[0034] S4: Pipe placement and inspection; Place the 9.4mm diameter thin-walled ceramic matrix composite pipe to be CVI treated stably on the supporting graphite cap 3; After placement, check whether the outer surface of the pipe is completely and evenly attached to the contact surface of the top of all supporting graphite caps 3 to ensure that there is no suspension or excessive local stress.

[0035] S5: Place the ceramic matrix composite pipe fittings, along with the supporting fixtures, into the deposition furnace for deposition.

[0036] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention and should be understood as not limiting the scope of protection of the invention to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed herein without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the invention.

Claims

1. A support fixture for the CVI process of thin-walled composite pipe fittings with a large aspect ratio, characterized in that: It includes a bottom template (1), a supporting round rod (2) and a supporting graphite cap (3); the bottom template (1) is provided with a number of supporting round rods (2) arranged in a rectangular array, and each supporting round rod (2) is equipped with a supporting graphite cap (3); the top of the supporting graphite cap (3) is provided with a semi-circular groove, and the ceramic-based composite pipe is supported in the semi-circular groove of the supporting graphite cap (3).

2. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 1, characterized in that: The upper surface of the bottom template (1) is provided with a number of mounting holes (11) at a preset interval; the bottom of the support rod (2) is provided with a boss structure (21), and the boss structure (21) is installed vertically in the mounting hole (11).

3. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 2, characterized in that: The supporting graphite cap (3) includes a hollow cylinder (31) and a semi-circular support part (32). The bottom of the hollow cylinder (31) is sleeved on the top of the supporting rod (2). The top of the hollow cylinder (31) is connected to the semi-circular support part (32). The semi-circular groove at the top of the semi-circular support part (32) is used to support ceramic-based composite pipe fittings.

4. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 3, characterized in that: The hollow cylinder (31) has an outer diameter of 12 mm and an inner diameter of 8 mm; the semi-circular groove at the top of the semi-circular support (32) has a diameter of 9.4 mm.

5. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 2, characterized in that: Each row of the supporting graphite caps (3) is arranged at equal intervals along the length of the ceramic-based composite pipe. The semi-circular grooves at the top of the supporting graphite caps (3) are aligned in the same direction, providing uniform support to the ceramic-based composite pipe.

6. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 2, characterized in that: The bottom template (1) is a graphite template; the graphite template is 1205mm long, 220mm wide, and 40mm high.

7. The support fixture for the CVI process of thin-walled, high aspect ratio composite pipe fittings according to claim 2, characterized in that: The diameter of the support rod (2) is 8mm and the height is 35mm; the bottom of the support rod (2) is provided with a 1mm boss; the material of the support rod (2) is C / SiC composite material.

8. A method for providing support fixtures for the CVI process of thin-walled composite pipe fittings with a large aspect ratio according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Place the bottom template (1) on the workbench; vertically insert the support rod (2) into the mounting hole (11) on the surface of the bottom template (1); S2: Fit the hollow cylinder (31) supporting the graphite cap (3) onto the top of the supporting rod (2), and install all the supporting graphite caps (3) one by one. S3: Calibrate the height of the installed support rod (2) and the orientation of the support graphite cap (3); S4: Place the ceramic matrix composite tube with a diameter of 9.4 mm to be treated with CVI on the supporting graphite cap; after placement, check whether the outer surface of the tube is completely in contact with the contact surface of the semi-circular groove at the top of all supporting graphite caps (3) to ensure that there is no suspension or excessive local stress. S5: Place the ceramic matrix composite pipe fittings, along with the supporting fixtures, into the deposition furnace for deposition.

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