Simulation of coating -visco-elastic liquid in the Micro-nip of metering size press
For a set of operating conditions and coating color formulations, undesirable phenomena like color spitting and coating ribs may be triggered in the Micro-nip during the coating process. Therefore, our interest in this work focus on another parameter affect on the undesirable phenomena as the vortices in the Micro-nip. The problem deals with the flow through the Micro-nip of metering size press. The flow enters and exits at a tangential velocity of 20 m/s between two rollers with diameter 80 cm and 60 mum apart. In the upper and bottom part of the domain the angular velocity is 314 rad /s. It has one sub-domain. Previous studies focus on the Micro-nip without considering the inertia and the viscoelasticity of the material. Roll coating is a technique commonly used in the coating industry to meter a thin fluid film on a moving substrate. During the film formation, the fluid is subjected to very high shear and extensional rates over a very short period of time. The fluid domain changes as a function of the hydrodynamic pressure within the nip as a result of the deformable cover usually used on one of the rolls. The free surface also adds more complexity to the flow due to the force equilibrium in the fluid gas interface. Last of all, the rheological behavior of the coating fluid is usually non-Newtonian, so the metering flow hydrodynamics is finally very difficult to describe. It is concluded that the normal forces of micro-nip increases with increasing the inhibitors. Therefore, it affects on the smoothness and creates defects. On the other hand, it can be concluded that the creation of big vortex in the middle of micro-nip affects on the coating liquid behavior.
Forward roll coating with deformable rolls: a simple one-dimensional elastohydrodynamic model
A simple one-dimensional elastohydrodynamic model of forward roll coating with deformable rolls is formulated and solved. It predicts the flow rate, pressures, and roll surface deflections in the nip between rollers, all as functions of one parameter, which can be conveniently chosen as either a dimensionless roll gap setting or load between rolls. The model predicts that for the small-deflection limit the coated-film thickness varies as R(μV)W−1, while for the large-deflection limit the coated-film thickness varies as R25 (μV)12E−13W−16 (μ = viscosity, V = roll speed, E = Young's modulus, W = load, R = roll radius). The range of applicability of these limits is defined, as are the operating characteristics in the intermediate region. Predictions of minimum roll surface separation compare well with published data.
Quasistatic indentation of a rubber‐covered roll by a rigid roll
The nonlinear elastic problem involving the indentation of a slightly compressible rubber-like layer bonded to a rigid cylinder and indented by another rigid cylinder is analysed by the finite element method. Both the geometric and material nonlinearities are accounted for. The finite element formulation of the problem is based upon a variational principle recently proposed by Cescotto and Fonder, and is valid for both slightly compressible and incompressible materials. The results computed and presented graphically include the shape of the indented surface, the pressure distribution over the contact surface, and the stress distribution at the bond surface. For the same contact width, the results for the compressible material are found to differ significantly from those for the case when the rubber-like layer is assumed to be incompressible.