Numerical modelling of the effect of operating parameters in the plastic blown film process

Abstract

The blown film process with polymer melts is modelled using non-isothermal viscoelastic rheological constitutive equations that are suitable for polyolefins. The model correlates the operating parameters such as mass flows, extruder temperature, tensile axial force and take-up force on processes such as bubble geometry and bubble temperature profile. Unlike Luo and Tanner [ Poly. Eng. Sci. , Vol. 25, 1985] who used the Maxwell constitutive equation, this study considers the viscoelastic Kelvin model that avoids any assumption regarding stress at the die exit. Like Luo and Tanner, the model uses shooting techniques to match the initial and boundary conditions from the freeze line and the die. The pressure drop and the take-up force are estimated as parameters that are optimized with the boundary conditions using the Nelder--Mead optimization method with Matlab. Effects of varying elasticity parameters and heat transfer coefficients on the bubble geometry, the pressure drop and take-up force are investigated.