Extrusion Processes

Extrusion is widely used for the manufacturing of polymeric products, permitting the preparation of highly uniform polymer melts at high rates. If polymers are placed in a tank or bucket and heated with an external heat source, the outer portions melt and remain hot, while the inner portions remain cool. This results in large temperature gradients, long heating times, poor temperature homogenization, and degradation of the outer portions, while the inner portions slowly heat and melt. Polymers are more efficiently melted by the viscous dissipation of mechanical energy in an extruder. The extruder rapidly melts the polymer in a thin film of melt, which is continuously removed, exposing fresh solid for melting. The extruder feeds solid polymer into the extruder and pumps molten polymer out for use in subsequent manufacturing processes. There are two broad categories of extruder: single-screw and twin-screw extruders.