Friction and Lubrication Mechanism of Radial Shaft Seals and Technical Trend

This paper focuses on rotating oil seals and details their friction control and lubrication mechanisms. Oil seals have the function of preventing fluid and gas from leaking inside machines and preventing foreign matter from entering from outside. With the development of synthetic rubber, materials with excellent heat resistance, oil resistance, and chemical resistance have been developed, and the performance of oil seals has improved. Oil seals consist of three elements: a rubber lip, a metal ring, and a spring. It is important to reduce friction at the lip. The main lubrication mechanism is the formation of a fluid film due to the microscopic roughness at the tip of the lip, which contributes to the reduction of friction coefficient. Recent studies have confirmed the existence of a fluid film using laser-induced fluorescence(LIF), but some phenomena that cannot be explained by elastohydrodynamic lubrication theory(EHL) alone have been observed. Toward the realization of a carbon-neutral society, low torque seals are required, and further elucidation of the lubrication mechanism is necessary to meet new applications. While the development of synthetic rubber and the application of optical technology have increased the reliability of oil seals, it is important to clarify the boundary lubrication characteristics between rubber and oil and to develop new evaluation methods for future technological development. Additionally, there is an increasing need in the robotics industry, and research on the sealed lubrication state of greases is underway.