Theoretical Analysis of Roll-over-web Coating of a Non-Newtonian Polymer Using Lubrication Approximation Theory

Roll-coating process plays an important role in many industries for its practical applications such as paint, PVC coated fabrics and plastic industries. There are several roll-to-roll coating methods including forward and reverse roll-coating. However, the roll-over-web coating study of the Rabinowitsch model is presented in this paper. The flow equations for the problem are developed and converted into dimensionless form with the help of dimensionless variables and then finally simplified by a well-known lubrication approximation theory. We employ the regular perturbation technique to get analytical expressions for velocity, pressure, and pressure gradient. Engineering quantities such as power input function and roll-separating force are calculated by Runge-Kutta method. The dimensionless Rabinowitsch parameter effect on velocity, pressure, pressure gradient, load-carrying force, and power input are shown graphically. It is interesting to note that for the shear thickening case, the Rabinowitsch model predicts 35% higher pressure, while in the shear thinning case it predicts 29% less pressure in the nip region when compared to the Newtonian model. The force and power show a decreasing trend on increasing the dimensionless Rabinowitsch parameter a. Moreover, the separation point shifts right of its Newtonian value when fluid behaves like shear thickening and volumetric flow rate increases which causes the coating thickness to increase.