Research of the gap effect over the crest of a barrier on the process of polymers extrusion

A mathematical model and numerical investigation of the dependence of the extrusion process of polymers on the geometric parameters of the barrier screw is given. The most typical designs of barrier screws, allowing intensify the melting process of recyclable materials are considered. The formulation of the problem, which includes the energy equation and the hydrodynamic equations and boundary conditions, is presented. Analysis of the data led to the conclusion that reducing the radial clearance increases dissipative heating of the molten polymer circulating over the barrier crest. First, it leads to a decrease of melt viscosity and consequently to reduction of the pressure at the outlet, and second it can cause the appearance or increase in areas of local overheating; that is, small gap above the crest of the barrier can lead to a decrease in output pressure and quality of the final product due to overheating of the polymer. On the other hand, the large magnitude of the gap may be a reason that the particles of solid, unmelted polymer melt will fall into the canal, which can also cause a decline in the quality of final products due to the jump of pressure and temperature at the outlet.