Don't overlook the feed section

Most extrusion screw designers often do not design the feed section with the same rigor as other screw sections. Optimum channel depth is largely a function of the solid properties of the polymer, such as bulk density, frictional characteristics, and solids flow properties. However, the melt viscosity of the polymer also enters into the depth considerations the lower the melt viscosity, the greater the feed depth required to maximize melting rate. The compressibility of the resin infeed material also has to be considered. So compression ratio has more than one meaning, and consequently is not a positive indicator for feed depth. The best way to evaluate the solid properties is by relying on your experience with each polymer, along with some simple tests. Measuring the angle of repose gives a good indication of the internal friction coefficient of the material.