Rolling of mozzarella cheese: Experiments and simulations

Mozzarella cheese is a visco-elastic-plastic shear-thinning material with a yield stress, which in a shear flow may be approximated by the Herschel–Bulkley model. The material was rolled in the SER extensional rheometer used as a rolling device with an aspect ratio of radius to minimum gap R/H0 = 4.3. For different feed thickness ratios and roll speeds, the exit thickness ratios and torques were measured and found to increase substantially with roll speed and initial sample thickness. Two-dimensional finite element simulations based on the rolling geometry and the rheological data provide yielded/unyielded zones, pressure, and stress distributions along the rolls. The results from the simulations are in good agreement with the experimental torque values but underestimate (by an order of magnitude) the thickness of the exiting sheets. It is argued that the latter is due to strong viscoelastic effects, which manifest themselves in free-surface flows, where (extrudate) swell becomes significant.