Direct observation of rolling interface of metal sheet by CCD Camera embedded into a roll and a study of lubrication mechanism

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A new rolling equipment for direct observation of rolling interface is developed. Into the upper roll of 157 mm in diameter of a two-high mill, a CCD camera with a macro lens is co-axially embedded. A transparent glass block preliminarily ground so as to match the curvature of the roll is also embedded in a radial direction. The two orthogonal axs are optically connected by a mirror locating on the roll axis. Signals are acquired through a slip-ring equipped at the edge of the roll. A digital video recorder enabled stabilized acquisition of images for over a minute at a rate of 30 images per second. Paraffinic base oils with varied viscosity were used as lubricants. A pure aluminium sheet of 2 mm thick and 40 mm width is rolled at a reduction of 5,10 or 15% at a rolling speed of 0.167m/s. The results are summarized as follows :(1) At the roll bite, a contrast connected with the thickness of the oil film is visible. The shape of the dark part (which is supposed to be the microscopic valleys of the sheet) is rich in the component parallel to the rolling direction.(2) At the exit of roll bite dendritic structure of the lubricant becomes more clear and parallel to the rolling axis. This is probably caused by the emission of a pressurized high-viscosity lubricant to the free space.(3) The lubricant staying on the glass tool shows relaxation as time passes. Thus, the dynamic behavior of lubricant viscosity should be taken into consideration in relation to the plasto-hydrodynamic lubrication.(4) Mirror finished sheets also showed similar lubricant behavior as the roll mill finished sheets. Another specimen with artifical microscopic cavities prepared by coining showed that the high viscous dendritic structure occurred through bearing areas.