Screw Extruders - an overview . R.P. Chhabra, J.F. Richardson, in Non-Newtonian Flow and Applied Rheology, 2008 3.9.3 Screw Pumps. Screw extruders, as used in the polymer processing and food industries, form a most important class of pumps for handling highly viscous non-Newtonian materials.Extruders are used for forming simple and complex sections (rods, tubes, etc).