Research of influence of barrier crest on polymer extrusion process

In this paper the effect of an additional (barrier) crest on heat and mass transfer processes and phase transitions of polymers in the channel plasticizing extruder is investigated. On the basis of the energy and hydrodynamics equations the mathematical model describing the processes of motion of a solid and a liquid polymer inside the channel as well as undergoing phase transformations is given. To create a mathematical model of melting processes a number of simplifying assumptions was introduced, namely: 1) the process has a stationary character at a constant mass flow rate; 2) helical path is unfolded on the plane and the principle of reverse movement is used; 3) diffusion of heat along the channel is not taken into account; 4) loss of the melt through the main ridge is neglected; 5) the elastic polymer in the melt process is not taken into account. As a result, the process of resin moving and heat exchange in the melting zone of the extruder was modeled by nonclassical heat and mass transfer in a long rectangular channel divided into two by barrier crest (solid phase channel and melt channel) in which the upper wall is moving at a constant speed equal to the peripheral speed of the worm at helical line cutting angle to the channel axis. The resulting model is solved by finite difference method allowing doing the numerical investigation of the dependence of the extrusion process of polymers on the geometric parameters of the barrier screw. The calculation was performed for the screw ME-90 with a number of L / d = 26 at a rate of 78.7 kg/hour. The width of the barrier crest was assumed to be 16 mm, clearance above the barrier crest was 1 mm. Feed material was high density polyethylene. Data analysis led to the conclusion that the presence of additional (barrier) crest increases dissipative heating of the molten resin circulating above it, as well as reduces the amount of molten polymer film on the solid phase, which allows intensifying melting process and improve its homogeneity.