Full Fluid Film Lubrication in Aluminum Strip Rolling

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Abstract
Rolling lubrication aims at reducing friction without endangering the stability of the process. This means that, in practice, a slight but positive forward slip is maintained, and lubrication is of a mixed hydrodynamic-boundary type. When fully hydrodynamic lubrication is attained, forward slip becomes negative, the strip skids in the roll gap, and thus a limiting condition is attained. These conditions were investigated for the specific example of 6061-0 and T6 Al alloy with uncompounded mineral oils of varying viscosities at various rolling speeds, giving forward slip ranging from slightly positive to highly (-80 percent) negative values. A comparison of measured and calculated roll forces showed that the flow stress is the single most important variable, and contributions of friction are negligible. The onset of skidding was a function of oil viscosity, bulk temperature, rolling speed and material flow stress, but could not be predicted from current theories of hydrodynamic lubrication. The rolled strip surface was matte and showed under the SEM deep hydrodynamic pockets. Calculated average film thicknesses gave reasonable limits of rolling without metal-to-metal contact.

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