Pressure and Viscous Heating Effect on Viscosity of Polymer Melts

1. y L x H/2 z W/2 Pressure and Viscous Heating Effect on Viscosity of Polymer Melts Benjamin Rudin, Max Schoengart, Tim Osswald Viscosity calculation Objective Motivation Experimental setup • The trend to thin wall injection molding in order • to save material has led to new versions of • injection molding like expansion injection • molding (EIM) For the Slit: • measuring rheological properties • under pressure • determine the pressure effect on • viscosity of polymer melts • Radial Functions Method (RFM) • according to the slit problem to • consider viscous heating effects, • determine a pressure shift factor • and validate experimental results Kistler 6157BB dynamic pressure transducers • viscosity: 3 pressures p1 , p2 , p3 range: 0 – 2000 bar Arburg Allrounder 320S Max injection pressure: 2500 bar • wall shear stress: thermocouple • Three pressure • transducers • measuring the • pressure along • the slit • corrected shear rate: • Two thermocouples control the constant • temperature of the rheometer • By injecting polymer with an injection molding • machine at a constant flow rate, viscosity • can be calculated. with ; n = power law coefficent • These technologies request high pressures. • To improve simulation results in engineering • predevelopments pressure effect on • viscosity has to be considered. Viscosity model RFM Results Temperature field 2D-field in the center of the slit: Measured pressures and temperatures temperature rise during a shot (viscous heating) Upper half of the slit flow rate: 6 ccm/s Material: Ticona Hostaform C9021 injection temperature: 200°C pressure factor: D3 = 5.75e-8 Cross model WLF-equation H = 0.67 mm W = 30 mm L = 200 mm VH = viscous heating • Viscosity curves • from slit • simulation: • Viscous heating • effect results in • lower viscosity. • Pressure effect • Implies higher • viscosity In this model the dependence of pressure on viscosity is respected by the parameter D3. In general the pressure effect can expressed with Collocation points: x-direction : 15 y-direction : 30 Boundary condition: Isothermal wall (TWall= const.) Use of symmetry Velocity at the wall is zero Max. temperature rise: 31.47 °C