Calendering of Newtonian and Non- Newtonian Fluids

Abstract

In this thesis, a theoretical analysis has been presented for the calendering process of incompressible Newtonian and non-Newtonian materials when they pass through the small gap between two counter rotating rolls. The calendering phenomena of a material flow between two co-rotating rolls to produce sheets of specific thickness and final appearance is an important process in many industries, such as the plastics, paper, rubber and steel industries for the production of rolled sheets of specific thickness and final appearance. In particular, the calendering of molten polymers is a process for the production of continuous sheet or film by squeezing the melt between a pair of heated counter-rotating rolls. A bench-top apparatus simulates the process. In this study two types of calendering processes are considered. In the first process, a molten material is transformed into a sheet by passing through a pair of rollers, whereas in second process a uniform film of liquid is deposited on a moving sheet. These two processes are quite similar, there is a convergingdiverging character to the kinematics, and we can expect the dynamics to be similar to that described in the first process. The major difference is in the character of the separation region, where the material splits and adheres to both moving surfaces. In the first process, it is assumed that the material separates clearly from the roll, whereas, in a second process, it is assumed that the material evenly wets both the roll and the sheet. The lubrication approximation theory (LAT) is outlined together with its calculations for viscoelastic and viscoplastic materials. Measurements of the gap between the roll surfaces, velocity and pressure profiles, film thickness, roll-separating force and power input to the rolls were made for a known roll speed and external load. The control of these engineering parameters are of excessive significance during the manufacture process.The goal of this work is to develop various mathematical models to characterize the effect of various materials in the calendering process.