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Summary:
The paper describes two finite element modelling approaches to represent the nip junction in a printing press. The dry contact model may be used to determine the stress levels which are present in the roller system and may be built using commercially available software. The wet contact model combines the fluid flow through the nip and the elastic behaviour of the rubber covering. Stable solutions were achieved in which the pressure field compared favourably with experimental data. The analysis also showed the very high shear rates which are present in the nip due to the pressure gradient and how this 'works' the ink reducing its viscosity as it passes through the nip. The subsurface stresses in the elastomer are controlled principally by the level of engagement, whereas the energy dissipation rate in the elastomer is controlled by the frequency of cyclic stressing and the stress levels induced. The flow through the nip was found to increase with the level of engagement due to the increased width of the contact and was also found to increase nearly linearly with speed due to the dominance of Couette flow through the junction.