Computer Aided Design for Polymer Extrusion and its Dies

Abstract

This research work concentrated on using Ansys poly flow software and equation of percentage root square error (PRMSR) to select the best viscosity model (viscosity vs. shear rate) at isothermal condition for polypropylene. The samples were tested at different loads and constant temperature 230oC using melt flow index tester. The results for each sample were recorded and different viscosity models were checked using Polyflow and the best of them was selected using PRMSE equation. It was found that shear stress versus shear rate was Non-Newtonian and the best model was (Carreau-Yasuda law). This model was used in analytical and simulation for die combined of two circular section tapered and non-tapered the pressure drop was studied at no-slip condition in the die wall. The governing equation of pressure drop was first derived to angle of tapered section,the best angle is 45o analytically and 45o ~50o for the simulation. For circular section the pressure drop was studied using different die lands and radii the results for die lands variations are almost the same but when varying the radius the results differ at radii less than 2 cm and approach each other at 2 cm and above. The swell ratio from this die decreased by small amount when die land was increased at linear pressure drop gradient, and it also decreased by high amount when L/D was increase at non- linear pressure drop gradient. In screw without and with nose models the maximum extruder output were stu-died at different parameters such as the extruder line the simulation of two screw models gave two points with specified flow rate and pressure drop less than analyti-cal value, the calculated pressure at flight clearance gave pressure that approached to simulation results than that at flight depth, as flight width decreased the analytical maximum output was not affected but in simulation was increased and pressure de-creased , when flight clearance decreased the analytical maximum output was not affected also but in simulation the output and pressure were increased, when screw depth increased the maximum extruder output and pressure in analytical and simula-tion was increased, as screw speed increased the maximum extruder output and pressure in analytical and simulation was increased, as length increased the analytical was not affected, but in simulation there was a fluctuation in flow and pressure and the best length of metering zone is (12cm) 2 flights this gave high flow rate and suitable pressure drop. In the die characteristics at operating point the maximum extruder output and pressure were studied at different parameters in the extruder line the same inter-sected of analytical extruder line at maximum output and pressure at calculated shear rate in die with the linear equation of simulated operating points, when width decrease the linear equations of output increase and pressure decrease, as flight clearance decrease the linear equations the output decrease and pressure increase these obesity results at the simulation without die was obtained before, when flight depth decreased the linear equations the maximum extruder output analytically and simulation tended to the same values but analytically pressure higher than simulation values, as screw speed increased the linear equations the maximum extruder output and pressure analytically and simulation tended to the same values , when screw length increased the linear equations the maximum extruder output analytically was constant and pressure increased, in simulation the output was decreased and pressure increased ,the screw length was not effect in output analytically but in simulation it was.