An empirical model for PVC melt drawing
During their fabrication into useful parts, all plastic materials undergo a complex deformation history. It has been common practice for rheologists to study the response of polymers to various idealized deformations in order to better understand their processing behavior. Great success has been attained in predicting the characteristics of polymer melts for processes in which shear deformations dominate. The pressure, temperature, flow rate interdependence in extrusion and injection molding processes can be described with suitable accuracy from relatively straightforward laboratory experiments. These shear experiments can also be used to elucidate other processing phenomena such as extrudate expansion, melt fracture, and thermal stability. However, rheologists have not yet been successful in identifying and measuring material characteristics which relate to processes involving essentially elongational deformations. Since nearly all fabrication techniques involve such deformations, the importance of extensional flow studies is clearly evident.
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