Castor oil is one of the most enormous potential environment-friendly lubricants, and used as the base oil and additives in industrial applications. In this paper, the rheological property of castor oil was investigated using the optical interferometric test rig to analyze its flow properties under the micro gap. These results indicated that the central film thickness of castor oil in the point contact zone underwent the initial increased and then stable variation with the entrainment speed at different temperatures. The temperature and entrainment speed played an important role on the lubrication state and oil shape variation along the transverse and entrainment direction. At low temperature, the contact zone was almost in the thin lubrication regime at low entrainment speed, but was in the elastohydrodynamic lubrication regime at high entrainment speed. The side leakage went through the initial increased then decreased trend with the temperature and entrainment speed. These research results would further develop the engineering application of castor oil.
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