​The application of graphite in aerospace

As a non-metallic resource mineral, graphite is widely used in the aerospace field due to its self-lubricating properties, easy forming and processing, good thermal conductivity, thermal stability and stable chemical properties, such as sealing materials, throat lining materials Wait.

Sealing material

The performance of the sealing material directly determines the reliability of the sealing. With the development and progress of science and technology, more and more stringent requirements are put forward for sealing materials. Because the space station has severe environmental changes such as high temperature, low temperature, high pressure, microgravity and corrosion, the sealing materials of the space station are mainly used in the propulsion system of spacecraft, the sealing of structural components such as wing ends and elevons, as well as hydraulic systems and pneumatics. Static seal and dynamic seal of box, valve and other parts in the system. However, due to the fast rotation speed of the engine shaft, the graphite material cannot meet the requirements for the tensile strength of the sealing material, so the graphite material cannot be used for the shaft sealing material.

1. Flexible graphite material

In the mid-1980s, the United States successfully developed a flexible graphite material made from deep processing of natural flake graphite. Due to its good self-lubricating properties and thermal conductivity, small linear expansion coefficient and friction coefficient, and large chemical inertness, flexible graphite materials can replace asbestos and rubber materials and are successfully used as sealing materials in high-tech fields. Flexible graphite materials have the characteristics of high compressibility and resilience, but extremely low strength, and can only be used for low pressure static seals.

2. Reinforced graphite material

Graphite material has poor sealing performance, and it is necessary to impregnate graphite with other materials (such as resin, metal, etc.) to improve its sealing performance.

(1) Resin impregnation: The resin is generally phenolic resin, tetrahydrofuran and furfurone resin. Jia Qian et al. studied the friction and wear characteristics of graphite materials impregnated with phenolic resin in different states, and concluded that the sealing material of liquid rocket engine turbopumps should have a moderate degree of graphitization.

The graphite material obtained from mesocarbon microspheres (MCMBs) by SongYZ et al. was impregnated with resin and pitch, and then carbonized at 500 °C to obtain a reinforced material. It was found that the increase of the impregnation and carbonization cycles reduced the porosity and increased the density of the material. The bending strength of the material is increased, the sealing performance is excellent, and it has a good application prospect in liquid rocket engines.

3. Isotropic graphite material

Isotropic graphite materials originated in the 1960s. Compared with other graphite materials, isotropic graphite materials have better comprehensive properties, and the molding process is also different. Generally, a cold isostatic press is used as equipment to convert petroleum coke. And pitch coke after special treatment as a raw material, the prepared isotropic graphite material has the characteristics of high compressive strength and bending strength, uniform and compact structure, high density, high precision and smoothness of the sealing surface after processing, and low porosity. , so it is also called high-density and high-strength graphite material.

Throat lining material

The characteristics of graphite material such as high temperature resistance, ablation resistance and light weight provide the conditions for it to become the throat lining material of small rocket solid rocket motor (SRM). In the late 1940s, solid sounding rockets in the United States were the first to use graphite throat linings. Later, the first generation throat lining materials (ATJ high-strength graphite materials) and the second-generation throat lining materials (G-90 high-density and high-strength graphite materials) appeared one after another. , the third generation throat lining material (Graphnol isotropic graphite material).

In the early 1960s, the silicon-infiltrated KS-8 high-strength graphite material jointly developed by the Institute of Metal Research of the Chinese Academy of Sciences, Xi’an Aerospace Composite Materials Research Institute and Jilin Carbon Factory can be used as the first-generation throat lining material. The KS-8 graphite throat lining material successfully solved the problem of thermal cracking due to the excessively thick silicon infiltration layer. Since then, the research on SRM has shifted from basic to model, which has laid a solid foundation for subsequent throat lining materials. KS-8 graphite throat lining material has been successfully applied to the final SRM of Dongfanghong No. 1.

As the requirements for all aspects of SRM continue to increase, graphite throat lining materials also need to improve their ablation resistance. In the mid-1960s, my country’s first-generation throat lining material T704 high-density and high-strength graphite material was independently developed by Shanxi Coal Chemistry Research Institute, Harbin Electric Carbon Research Institute and Xi’an Aerospace Composite Materials Research Institute. In the early 1980s, the T705 graphite material jointly developed by Harbin Electric Carbon Research Institute and Xi’an Aerospace Composite Materials Research Institute has greatly improved ablation resistance, and has been used in various small tactical bullets such as SRM throat linings that are resistant to high temperature and oxidation. parts are widely used.

T707, T715 and T711 graphite materials have ablation resistance and can also be used as throat lining materials for small rockets SRM, which belong to the second generation of throat lining materials in my country. The isotropic CDK-20 graphite material developed by Chengdu Carbon Co., Ltd. can be used as the third-generation throat lining material of small rocket SRM by using the isostatic pressing process, and is undergoing application research.


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