Optical Interferometric Observations of Oil Film Behavior in Reciprocating Rubber Seals

The behavior of oil films formed between two types of nitrile rubber seals and an oscillating glass plate is examined by means of optical interferometry. The friction force is also measured. The average oil film thickness takes a maximum near the center of the stroke and minima at both ends of the stroke, and their values increase with increasing reciprocation frequency. The friction force is markedly influenced by the thickness of oil film; generally, the thicker the oil film, the lower the friction force. In particular, the aeration produced at the oil side region near the end of the motoring stroke results in a large increase in the friction force in the succeeding pumping stroke. The results obtained are explained based on the inverse hydrodynamic lubrication theory and the observed oil film behavior.