It is today possible to manufacture so smooth surfaces that they can elastically conform totally to each other over the whole Hertzian contact area. For pure rolling lubrication such surfaces only need an oil film of molecular dimensions to get total separation. When the rolling motion is combined with sliding, the pressure fluctuations inside the Hertzian contact redistribute the oil and make metal-to-metal contact possible. The redistribution velocity is a function of the slip rate $S$ and the number of asperities $N$ from the inlet to the outlet of the Hertzian contact area. The asperity top oil film thickness decreases with a factor of the order $2NS$ going from the inlet to the outlet of the Hertzian contact.

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