Non Isothermal Flow Dynamics and Viscous Heat Generation in Polymer Melt Extrusion
Non-isothermal viscous dissipation drives core melt temperature spikes that cause extrudate defects if die land geometry is not scaled to shear rates.
Interfacial Friction
Meaning
Mechanical interactions at the boundary between two distinct materials define the resistance to movement during contact. In plastic processing, interfacial friction occurs where the solid polymer pellets rub against the metal walls of the extruder barrel. It is the primary mechanism for generating the pressure needed to move material forward.
Surface Contact
The roughness of the metal and the texture of the polymer determine the coefficient of the bond. If interfacial friction is too low, the screw will turn without pushing the material, a condition known as solids conveying failure. Excessive friction can lead to premature melting or localized burning of the resin.
Energy Transfer
Work performed to overcome the resistance at the boundary is converted into heat. This interfacial friction provides a large portion of the energy required to reach the melting point of the polymer. The rate of this transfer depends on the screw speed and the pressure within the feed section.
Wear Rate
Constant rubbing between the materials eventually removes metal from the barrel and screw surfaces. Monitoring interfacial friction helps predict when components will need replacement or refurbishment. High rates of wear increase the cost of production and can introduce metal contaminants into the finished goods.