The Film Behaviors of Grease in Point Contact During Microoscillation |
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Authors: | Gang Li Chenhui Zhang Hongyi Xu Jianbin Luo Shuhai Liu |
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Affiliation: | (1) State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China |
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Abstract: | Microoscillation is a typical case of transient motion, which occurs in many machine elements, including rolling or sliding
element bearings, cams, and gears. Wear is easy to occur on the surface of such elements, particularly at the end point of
the stroke, where the surfaces are momentarily static. In the present work, an experimental investigation is conducted to
explore the grease film behavior of point contact lubrication during microoscillation in the case of pure rolling or pure
sliding. The technique of relative optical interference intensity was used to monitor the variation of the grease film thickness
and the motion of the grease in the contact area through analyzing the captured interferograms. Experimental results indicate
that a crescent-shaped grease film can form along the motion direction in the contact area under microoscillation. The grease
film is formed in the inlet region, and the film thickness remains while moving in the Hertzian contact area. In the case
of pure rolling, the crescent-shaped grease film and the initial entrapped grease film are carried by a tow effect of moving
interfaces in the contact area. However, in the case of pure sliding, there are relative motions in the sliding direction
at the two interfaces of the grease/ball and the grease/disk in the Hertzian contact area. The shape of the entrapped grease
remains almost unchanged while moving in the Hertzian contact area. During the repetition of microoscillations, the crescent-shaped
grease film thickness drops gradually. |
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