The effect of different work roll diameters, different circumferential speeds of work rolls, and different friction for top and bottom side on roll parameters, especially on curvature of outgoing material, is investigated. Three methods, which are all based on the theorem of the upper bound of total power, are discussed. Their results are compared with experimental data of Juretzek. They differ in the kind of velocity field for the material flow in the roll gap. The first makes use of a polynomial global velocity field. The second employs bilinear quadrilateral finite elements, which are fixed to space, while the stationary rigid plastic material flow goes through (stationary FEM). The third field consists of rigid triangles which can slide along their contact lines. The last method produces a formation of shear lines, which is in good coincidence with that of the zones of high strain rate, given by stationary FEM. Results of parameter studies using stationary FEM are shown as relationship between dimensionless characteristic numbers. At last a comparative analysis of the effectiveness of the different methods is given.
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