Friction inhomogeneities in cold rolling

The friction conditions between strip and work roll are practically never homogeneous. Three different kinds of friction inhomogeneities, typical for technical strip rolling applications, are discussed: The first one is the increase of the friction coefficient from entry to exit of the roll gap. Measured force and forward slip data is used to recalculate this increase by applying an enhanced Bland–Ford theory. The second one is the case of different friction over the strip width. The influence on flatness is shown. The third one is the effect of frictional instabilities like stick-slip, which may induce time-dependent asymmetry between top and bottom side, and therefore corrugations.