SHAPING PROCESSES FOR PLASTICS Chapter 13- Part 1 Properties of Polymer Melts Extrusion. Manufacturing Processes, 1311 Dr Simin Nasseri Southern Polytechnic State University. SHAPING PROCESSES FOR PLASTICS. Properties of Polymer Melts Extrusion Production of Sheet, Film, and Filaments
Manufacturing Processes, 1311
Dr Simin Nasseri
Southern Polytechnic State University
Viscosity of a polymer melt decreases with shear rate, thus the fluid becomes thinner at higher shear rates.
(Newtonian Material: Viscosity changes by temperature, not by time or shear rate)
Figure 13.1 Viscosity relationships for Newtonian fluid and typical polymer melt.Viscosity and Shear Rate
Shear rate Viscosity
Figure 13.2 Viscosity as a function of temperature for selected polymers at a shear rate of 103 s-1.
Die Swell the fluid becomes thinner at higher shear rates.
Figure 13.3 Die swell, a manifestation of viscoelasticity in polymer melts, as depicted here on exiting an extrusion die.
Vortices: If you stir water or iced tea (Newtonian liquids) vigorously (but not too vigorously!), you may see tiny "swirls" parallel to the axis of stirring. The flow is downwards.
Polymer is transformed into fluid, air mixed is extracted, and material is compressed.
Melt is homogenized and sufficient pressure developedto pump it through die opening.
Feedstock is moved from hopper and preheated.
Extrusion bridge die making a hollow section product. Note that in the picture the die has been split to show the material passing through it. In reality, the die and the ring fit together, with a gap for the extruded material to flow through.
3- Metering Section the fluid becomes thinner at higher shear rates.
2- Compression Section
1- Feed SectionTest yourself!