Analysis and Evaluation of the Spreading Mechanism of Solid Lubricant under Low-Speed and Heavy-Load Graphite Inlay Lubrication

Copper-based graphite inlay lubrication technology has become a key pillar of engineering and technology, providing reliable solutions for many critical applications. Especially in the deep space and deep ocean fields, many important components need to operate in extreme environments, and higher requirements have been put forward for the performance of sliding bearings. Copper-based graphite Inlay lubrication is an integral part of these applications due to its unique properties, including low friction coefficient and excellent wear resistance. For example, sliding bearings perform the critical task of supporting rotating parts and reducing friction losses in aircraft engines. This lubrication method could effectively reduce mechanical wear and extends component life while improving overall performance and reliability. Besides, the lubrication method is also widely used in large gate bottom pivots to ensure the smooth operation of the gate, especially in important occasions that require long-term stability. Although some studies had revealed how copper-based inlay lubrication works, there are still some unresolved issues, such as the quantitative analysis of the formation of solid lubricating films. In order to clearer understand the composition of the lubrication film in the low-speed and heavy-duty condition for graphite inlay lubrication, especially the migration rule of C element, the UMT-2 multi-function friction and wear testing machine had been adopted to simulate the pin-disk test in the low-speed and heavy-duty conditions. Then the energy spectrum analysis was carried out on different locations of the same path on the specimen surface to study the influence of different surface roughness, friction velocity and load on the migration of C element during friction. The test results showed that the content of C element in the wear marks increases under three conditions: the surface roughness increases from R_a=0.8 μm to R_a=2.0 μm, the friction velocity decreased from 0.06 m/s to 0.02 m/s and the load increased from 100 N to 175 N. Through data fitting, it was found that the lubrication failure distance could reach 0.067 m under the conditions of velocity 0.03 m /s, load 150 N and surface roughness R_a= 1.6 μm. When the speed was only 0.02 m/s, the lubrication failure distance was 0.344m. When the load was only changed to 100 N, the lubrication failure distance was 0.119 m, which indicated that lower speed and smaller load were helpful to improve the lubrication performance and the stability of the lubrication film, and lengthen the lubrication failure distance. On the contrary, the higher speed and the larger load would affect the stability of the lubrication film, resulting in the shortening of the lubrication failure distance. These results revealed the quantitative migration rule of C element under this working condition, and provided a theoretical basis for optimizing the position parameters of solid lubricants for sliding bearings under low-speed and heavy-load. These research resultes would hopefully drive further improvements in the design of sliding bearings in the future to provide solutions with higher performance and reliability.