The Autogenetic Screw The extruder screw at steady state is typically assumed to be totally thermally isolated from the polymer (adiabatic.) How can this be if the screw is cold at the inlet and hot at the exit? This temperature difference must be accompanied by heat flow along the axis of the screw. Therefore, there must be heat transferred to the screw at the hot end to supply the axial heat flow. This heat can only come from the polymer. The screw can not be adiabatic with the polymer at steady state.

So, how can the screw be at steady state when the polymer is adding heat? There must be an equal an opposite loss of heat elsewhere to the polymer and drive end. The sum total of all heats is then zero when steady state exists. This type of operation has been dubbed autogenous or autogenetic. Therefore, analysis or discussion of extrusion to any level of sophistication must take into account the fact that the screw is interacting thermally with the polymer.