Rheological Modeling for Production of High Quality Polymeric
The fundamental defect inherent to the thermoforming technology is wall-thickness variation of the products due to inadequate thermal processing during production of polymer. A nonlinear viscoelastic rheological model is implemented for developing the process model. This model describes deformation process of a sheet in thermoforming process. Because of relaxation pause after plug-assist stage and also implementation of two stage thermoforming process have minor wall-thickness variation and consequently better mechanical properties of polymeric articles. For model validation, a comparative analysis of the theoretical and experimental data is presented. Keywords—High-quality polymeric article, Thermal Processing, Rheological model, Minor wall-thickness variation.
Simulation of Thermoforming and Blowmolding — Theory and Experiments
The increased use of polymers in the fabrication of various products ranging from beverage bottles, automotive fuel tanks, food trays, to refrigerator liners has made it important that minimum requirements on part thicknesses be met when forming plastic parts. The two primary industrial processes for forming both small and large, thin walled plastic parts are thermoforming and blowmolding. Generally, during these processes, polymers behave in a viscoelastic manner and their deformation process involves large deformations, large strains, large strain rates, contact between the hot polymer and the mold wall, and physical instabilities may also occur during inflation. However, in thermoforming and blowmolding, especially when plug assisted, the process occurs rapidly and at a strain rate high enough for the elastic effects to be dominant and there is no time for viscous dissipation. The polymer undergoes a large elastic deformation.
Blowing of oriented PET bottles: Predictions of free blown size and shape
A model of the blowing process for polyethylene terephthalate stretch blowmolded bottles is presented. This model uses a rubber constitutive relation. The free blown diameter and the stretch balance are derived from stress equilibrium. Free blow experiments show good agreement with the predictions.